Sciencemadness Discussion Board

Laboratory Tips and Tricks

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Panache - 20-12-2009 at 23:28

One of the things i miss about working in Industry is that you pick up little things here and there that make you more competent and make life easier.
To an extent some of this interaction is facsimiled here on ScienceMadness but not really in a formalized sense.

So this is me trying to set up a thread for people to write in little tips and tricks and also for people to ask about simple laboratory techniques.

I'm looking forward to picking up some new tricks, the last one was sometime ago, one of the Euro members showed how placing a glass rod across a beaker allowed one to direct the flow out of the beaker quite accurately. I use this all the time now.

Also as i work alone largely i'm equipped with many of my own innovations to simple things. I have now a place i can merrily bleat away about them and in that vein here's a couple of things.

1.Low boiling solvents (dcm, ether, acetone etc) are excellent for their ease of distilling but are a pain for doing vacuum filtrations with as the solvent can easily boil in the flask, or worse still in the filter. To circumvent this when filtering low boiling solvents i pull a full vacuum on a round bottom of appropriate size, tap it, then use this a the vacuum source and filter flask. The solvent then has nowhere to go if it boils.
Useful for this technique are some decent taps with groundglass sockets each side. I have a wizz bang 15mm bore, 34/35, vacuum tap i use for this now but initially i used vacuum tubing, less elegant but completely servicable.

2. A really inexpensive dessicator cabinet can be had out of any refrigerator or freezer. One just need ensure that the seals are sound then plonk some trays of CaCl2 in for a few days and voila. I actually also now keep my dessicators in my glass side and fronted hospitality fridge that i got for nothing as it was sans compressor. Which i didn't want anyway. Under bar fridges can be had for almost nothing brand new now.

There you have it!

More to come!

User - 21-12-2009 at 07:41

Quite a while ago I was very annoyed when i needed to evaporate a solvent.
I dissolved a synthetic rubber so crystallization or evaporation by heat wasnt really going to do the trick.

Well I came up with a very simple device do the job.
I took a piece of PVC pipe about 20cm diameter 35cm long.
Placed an old cooling fan on top (quite powerful one from a professional fridge)
Glued the thing together.

The pipe is placed on top (over) a beaker with solvent and the power is turned on.
The ventilation/airflow is strong enough to cause a vortex in the solution.
100ml of petrol was evaporated within 20 minutes without heating, i think the temp in my lab was around 17 degrees celsius.

I was very pleased with this.
I didnt have a vacuum source that days and it really was good solution.
The thing is still used now and then.

[Edited on 21-12-2009 by User]

[Edited on 21-12-2009 by User]

Sedit - 21-12-2009 at 10:03

Quote:
2. A really inexpensive dessicator cabinet can be had out of any refrigerator or freezer. One just need ensure that the seals are sound then plonk some trays of CaCl2 in for a few days and voila. I actually also now keep my dessicators in my glass side and fronted hospitality fridge that i got for nothing as it was sans compressor. Which i didn't want anyway. Under bar fridges can be had for almost nothing brand new now.


As far as dessicators go I always found a large zip lock bag filled with MgSO4 to work for almost anything I need it for. Of course if its not strong enough you can substitute your favorite drying agent but all one has to do is add alot of drying agent in the bag and place your jar of material inside and seal for a few days or more. I mostly use it for drying nitrites since I find it very difficult to dry KNO2 made thru the reduction of nitrates and carbon.

aonomus - 21-12-2009 at 10:49

For smaller scale evaporations that I want to go faster, I set up an aquarium pump with a pipette attached to the tubing, aimed at the liquid to be evaporated in a beaker. Works quite well. I can use this setup on a hotplate to keep the temperature warm, or just leave it at RT for however long I want.

Another trick that I've found works quite nicely for a dessicator is to use MgSO4 or CaSO4 in the bottom of a larger metal tin container with those plastic snap on lids. Its not absolutely air-tight, but there isn't any appreciable airflow to be a problem. I put 4 even sized blocks (wood, plastic, metal, whatever, its just a support) in a square arrangement, then a layer of MgSO4 at the bottom, and then drop in a circle of pegboard material (which sits on the blocks) to give an even surface to put containers on. Extra points for putting a small loop of string or something else so you can actually lift the pegboard out when you need to replenish the dessicant.

Even one of those containers coffee or non-dairy powdered creamer works well. Just wash it out and dry before using, and make sure its never used for food again!

Edit: edited for clarity on what the 4 blocks are for

[Edited on 21-12-2009 by aonomus]

UnintentionalChaos - 21-12-2009 at 11:37

You can go over to walmart and buy some new fancy schmancy locking tupperware (the brand I have is called lock and lock I think). They have a rubber gasket around the rim and are quite airtight. They make a good cheap non-vacuum dessicator for <$10. The bread box size is very convenient and stores several 400ml beakers, small flasks, or reagent bottles and a dish of sulfuric acid.

[Edited on 12-21-09 by UnintentionalChaos]

User - 21-12-2009 at 15:44

Lol a very small trick one of my chemistry teachers ones showed me.
( he was an old guy, madprofessor like type)
He'd cut of a small piece of the typical red rubber tubing the one used for condensor cooling feed/return.
Then he splitted it in 2 pieces and cut them both open in the lenght.
He than shove it over his vingers so he could pick up hot beakers from the hotplate.

I liked his style :)
He was a very wise and gentle old man.
We used to smoke together during the breaks, he smoking his pipe.
Those were some good days.

[Edited on 21-12-2009 by User]

aonomus - 21-12-2009 at 17:33

UnintentionalChaos: I'll have to take a look next time I'm at Walmart, I never thought of using that kind of tupperware before. It would probably be better than my current ever so transparent metal can </sarcasm>.

I have another tip thats mixed in with a question. I like to standardize connectors across my electronics workbench when I can, and also do so with my cooling water setup.

I use Anderson Powerpole connectors that are hermaphroditic and allow any connector to mate with another. I have made up many cables that range from adapters to voltmeter/ammeter arrangements, extensions, fuses, etc. Essentially I can create a cable for anything from bits that I have sitting around.

I'm wondering if there is anything similar for low-pressure water? I find myself using my Liebig condenser interchangably as a distillation condenser or for refluxing (not efficient, but convenient), and needing to switch around my friction-fit gendered quick disconnects to have the water input at the top or bottom of the condenser as needed. I'm hesitant to buy expensive quick-disconnects (eg: ball-lock connectors) only to find out that I will need to detach and reattach them anyway, so I'm looking for something that is better than just a barbed to barbed fitting, but inexpensive and somewhat standard.

I have been considering the quick disconnects used by water cooling for PCs, although these might be just as expensive...

Panache - 23-12-2009 at 04:35

Quote: Originally posted by aonomus  


I'm wondering if there is anything similar for low-pressure water? I find myself using my Liebig condenser interchangably as a distillation condenser or for refluxing (not efficient, but convenient), and needing to switch around my friction-fit gendered quick disconnects to have the water input at the top or bottom of the condenser as needed. I'm hesitant to buy expensive quick-disconnects (eg: ball-lock connectors) only to find out that I will need to detach and reattach them anyway, so I'm looking for something that is better than just a barbed to barbed fitting, but inexpensive and somewhat standard.

.

Not only that the friction fit have this tendency to go 'snap' at the glass barb, i completely agree with you and i circumvent it by using a short piece (like 7cm) of goodyear ortac tubing, permaqnently on the barbs, i then use the clear pvc tubing that easily inserts and removes from the ortac rubber tubing. I also get a bit silly and taper out the Ortac tubing slightly with a tapered die grinding bit ( a drill bit could work) to make life ever so much sweeter again.

I find the quick connects leak appreciably simply because they are hand tighten and can easily untighten. Using a pair of pliers to tighten them defeats the purpose of their convience in the first place.

aonomus - 25-12-2009 at 11:31

The friction fit disconnects that I have been using are this type: http://www.usplastic.com/catalog/item.aspx?itemid=23016&... . There seems to be some confusion as to what I was meaning, and you are right Panache that simply putting on tubing over the barbed fittings is asking for breakage (especially if its a reflux or Friedrich type condenser with a 90deg bend in the tube). The quick disconnects that I use so far are useful, but they require flipping around whenever I want to change the direction of water flow through the condenser...

I've been doing some looking and I found some nice quick disconnects that are very cheap, and come in different sizes, shapes, and versions: http://www.usplastic.com/catalog/item.aspx?itemid=23885 . There are even versions that automatically shut off flow, and while they are probably leaky to some degree, at that price I'm tempted to get some to try out.

Panache - 25-12-2009 at 12:33

i get you, yes i was referring to sliding the hose over the barb. Those seem neat but are kind of large to be hanging off your condenser, i guess you would have a length of hose off the condenser before them.

Panache - 25-12-2009 at 13:10

For those using older vacuum pumps (like myself) a vast increase in performance can be achieved simply by switching to a fully synthetic vac pump oil. In Australia by far the most widely available oil is one by Caltex, i don't recall its exact product name but it is available at BOC gases. This oil is derived from crude oil, and whilst it does the job it is better to use the CPS brand vac pump oil from the USA, fully synthetic and quite great. Usually only stocked as a 500mL bottle get them to ship in a 4L for you as it's considerably cheaper. This pump oil is stocked by Heatcraft stores nationally (they are a refrigeration supplier, leave yourself sometime to peruse the shelves as many interesting products exist including mol sieve dryer cores).

Rosco Bodine - 25-12-2009 at 13:31

Amalgamated scrap aluminum makes an excellent dessicant leaving nothing but a predominately dry nitrogen atmosphere over dry samples which previously were damp and residing in moist air. The aluminum exposed by having its protective oxide disrupted by amalgamation is very actively chemically oxidized and hydrolyzed to a pile of alumina. A vacuum release is needed because the removal of the oxygen from the air over the sample results in an indigenous partial pressure, which also hastens the dessication of the sample into the dry nitrogen residue which remains from what was originally the captive air.

Panache - 25-12-2009 at 15:57

Quote: Originally posted by Rosco Bodine  
Amalgamated scrap aluminum makes an excellent dessicant leaving nothing but a predominately dry nitrogen atmosphere over dry samples which previously were damp and residing in moist air. The aluminum exposed by having its protective oxide disrupted by amalgamation is very actively chemically oxidized and hydrolyzed to a pile of alumina. A vacuum release is needed because the removal of the oxygen from the air over the sample results in an indigenous partial pressure, which also hastens the dessication of the sample into the dry nitrogen residue which remains from what was originally the captive air.


The vacuum release needed is only for practical purposes i assume (ie getting the chamber open) not for any safety reasons.

Awesome trick though, who needs any other desiccant.

Rosco Bodine - 25-12-2009 at 19:34

Your assumption is correct. Full disclosure requires I should identify that my suggested use of aluminum amalgam as a dessicant is intuitive in origin rather than empirical. However I do have confidence that my belief or faith has rational basis rather than being unfounded superstitious nonsense. The proof will be in the pudding.

[Edited on 26-12-2009 by Rosco Bodine]

ziqquratu - 25-12-2009 at 20:06

Wouldn't the hydrogen formed in the reaction of the aluminium with water more or less compensate the pressure drop due to absorption of oxygen? Depending on the humidity, could it not in fact result in a build up of pressure? (which could cause the lid of the desicator to "pop", thus potentially re-exposing it to air...).

Neat trick if it works, particularly for anything oxygen sensitive. Perhaps an oil-filled bubbler might be more appropriate if excess pressure was shown to be a problem.

Rosco Bodine - 25-12-2009 at 20:30

It could very well develop a positive pressure of hydrogen, if there was sufficient moisture in the sample to offset the oxygen loss, and the dessicator lid would lift occasionally and vent the byproduct hydrogen. So it would be a good idea to have a loosely fitted ring clamp around the center to allow a slight vertical movement of the dessicator lid to accommodate any venting, without allowing enough horizontal movement as would cause the lid to not settle back down again to a seal. The lid would actually function as a sort of check valve. Hydrogen is extremely dessicating by itself IIRC, so this should actually be helpful. The ultimate dewpoint should be very very low.

DJF90 - 26-12-2009 at 12:16

Use the amalgamated scrap in a vacuum dessicator and the pressure problem is null. However I dont really like the sound of having mercury in a vacuum dessicator, and also, how to dispose of the mercury contaminated alumina when its done with?

aonomus - 26-12-2009 at 12:51

Quote: Originally posted by UnintentionalChaos  
You can go over to walmart and buy some new fancy schmancy locking tupperware (the brand I have is called lock and lock I think). They have a rubber gasket around the rim and are quite airtight. They make a good cheap non-vacuum dessicator for <$10. The bread box size is very convenient and stores several 400ml beakers, small flasks, or reagent bottles and a dish of sulfuric acid.

[Edited on 12-21-09 by UnintentionalChaos]


So walmart had a set of lock&lock containers on special, I bought a set for the parents, and kept the largest one. I used little disposable plastic containers that are used for serving sauces, etc with your food to hold NaOH pellets (I also use these as weigh boats since I got them for free).

The container is probably only about 2.5-3 inches tall, so its not enough for a large beaker. Its still quite useful since I can happily place little 30mL scintillation vials that I use to store stuff in. Perfect for storing all my small-scale products that need dessication in.

I'll report back when I find a larger lock&lock container when I find one.

Fleaker - 26-12-2009 at 16:59

Quote: Originally posted by DJF90  
Use the amalgamated scrap in a vacuum dessicator and the pressure problem is null. However I dont really like the sound of having mercury in a vacuum dessicator, and also, how to dispose of the mercury contaminated alumina when its done with?


What of using gallium in lieu of mercury? It too interferes with the surface formation of alumina.


Something I've often wondered is if one could substitute gallium or a gallium salt in place of mercury for Hg-Al reductions. Gallium may be more expensive than mercury, but it's far less toxic.
I gave a very cursory check to the literature but saw nothing specific.

aonomus - 26-12-2009 at 21:51

I also wonder if you could use gallium/gallium salt as a substitute for initiating Grignards, or the formation of aluminum isopropoxide?

not_important - 27-12-2009 at 04:07

Gallium works well for getting Al to react with water, but I believe it has more of a tendency to sink into the bulk metal along grain boundaries which might slow reactions down.

Another potential issue is that Ga is noticeably more reactive than Hg, and so may get into side reaction in the case of Grignards even though you'd expect the even more reactive Al to keep the Ga in metallic form.

US patent 4745204 is the use of gallium as the catalyst for making alkoxides, US patent 4358291 is similar but had the Al dissolved into Ga or Ga-In alloy. From the first patent:
Quote:
It has also been suggested to use aluminum dissolved in gallium or gallium-indium alloy for dehydration of liquid materials such as alcohols. See Cuomo, et al., "Dehydration via Gallium-Activated Aluminum", IBM Technical Disclosure Bulletin,Vol. 24, No. 2, July 1981, p. 1080.


This would seem to make both the use in the drying application, and the production of alkoxides, very likely to be practical. The low vapour pressure of gallium means you'll lose none that way; when most of the Al is gone treat the Al-Al2O3 with some hot water to get all into the oxidised state, then extract Ga with aq. HCl. Even if some Al goes along it still should work to activate further Al. H2SO4 might be a better acid to use, as it's less likely to drift around inside the desiccator. For making alkoxides first react with GaCl3, a quick water rinse, then another rinse with the alcohol, should remove the chloride; finally popping the activated Al into the main batch of alcohol.



sonogashira - 27-12-2009 at 05:25

Not-quite in answer to a question above... But still, a 'tip' :)

Br2 is better than I2 for starting Grignard reactions.

(I read this in an orgsyn paper - I forget which, but a drop of Br2 in place of a crystal of I2 was the recommendation. In fact all of these papers are full of 'tips' from very experienced chemists).

[Edited on 27-12-2009 by sonogashira]

DJF90 - 27-12-2009 at 06:10

Sonogashira: I too am sure I have seen this before. Iodine is best used thusly: Set up the dry apparatus, and add the magnesium and iodine to the flask (with a stirbar). With mag stirring turned on, heat the flask with a heat gun to make the iodine vaporise a bit; this greatly improves its activation of the magnesium, and i've yet to have a grignard fail on me using this method.

The other method I have seen used quite often is addition of (CH2Br)2, to the reaction mixture containing enough magnesium metal to react with the organohalide you want to form the grignard reagent from AND the ethylene bromide added as an entrainer. I'm tempted to try this one at some point.

sonogashira - 27-12-2009 at 06:43

^ Yes, I think that is used as a nicer form of Br2 (the ethene goes)

aonomus - 27-12-2009 at 08:20

Another thing with gallium is that it wets glass unlike mercury, wouldn't that make it a pain to clean off?

UnintentionalChaos - 29-12-2009 at 08:07

Quote: Originally posted by aonomus  
Another thing with gallium is that it wets glass unlike mercury, wouldn't that make it a pain to clean off?


I believe the reactivity is similar to tin. Stong HCl should remove any residue in a hurry.

User - 29-12-2009 at 11:54

Another trick popped to mind.

Sometimes it does happen that one spills something like strong acid, base or whatever.
Cleaning can be messy and a quite unpleasant experience.
there is a very easy and cheap solution to the problem.

Use kitty litter!

This material (often made out of bentonite) is very absorbent and can suck up an amazing amount of liquid which afterwards can be disposed with great easiness.

The cheapest brands often contain the least "contaminations" and proven to work best imo.
There actually is a professional alternative on the market,
but this is way cheaper and came out as a brilliant solution a couple of times.

For the ones that did not know this I hope you like it.

aonomus - 29-12-2009 at 12:08

Another trick that I've been using recently is using a claisen adapter with 2 gas inlet adapters fitted to a large RBF to do filling operations. Essentially, pull vacuum on the higher one, and use a tube to siphon liquid from a large container until the flask is full to the level you want. Much safer than attempting to lift buckets high and risk getting stuff spilled.

Only catch is that your tubing limits what you can use this with.

Panache - 1-1-2010 at 20:11

If you have a dead hard drive, open it and get out the rare earth magnet (providing the HD is circa this century). This makes a great tool for holding magnetic stirrer beads fast onto the bottom of your flask when pouring or transferring its contents.

aonomus - 1-1-2010 at 20:52

So I saw at Walmart a few days ago a medium sized glass cookie jar. Likely not pyrex, and definitely not strong enough to withstand vacuum, but for a plain old desiccator, it would work great. Just need to add a separator to allow beakers to sit above the desiccant. Its taller than the small lock&lock container, and would let me place larger beakers inside.

As for the hard drive magnet (and other magnets), I have realized that the sudden increase in force when you bring the magnets together is sometimes enough to pinch fingers and maybe even scratch or chip the glass. I want to coat my magnet in plastidip, but can't justify buying it (its somewhat pricey) for only 1 project. A cheap substitute are a few layers of paper towel that help cushion the forces.

Oh, and a word of warning for anyone that wants to add copper metal mesh (from copper pot scrubbers) to a hempel column to scrub any sulfur compounds from the vapors: its not pure copper, its copper plated steel, and thus, rusts.

Edit: Another word of warning - clear PVC tubing at 0degC is a bad thing. I use tygon tubing in the entire coolant loop except for 2 short stubs of PVC that connect the glass tubing connectors to some plastic quick disconnects. To my horror I discovered that the tubing had become rock hard, so hopefully no flexing occurs allowing it to crack.



[Edited on 2-1-2010 by aonomus]

Panache - 19-1-2010 at 05:22

Quote: Originally posted by aonomus  

As for the hard drive magnet (and other magnets), I have realized that the sudden increase in force when you bring the magnets together is sometimes enough to pinch fingers and maybe even scratch or chip the glass. I want to coat my magnet in plastidip, but can't justify buying it (its somewhat pricey) for only 1 project. A cheap substitute are a few layers of paper towel that help cushion the forces.


[Edited on 2-1-2010 by aonomus]


Wrap it around several times with polyethylene film (aka that stuff you wrap your sandwiches in) then either flame it shut or oven, its now spongy and durable!

Of course your could just gently place the magnet on the glass.

aonomus - 19-1-2010 at 06:37

Good strong rare earth magnets sometimes jump, despite trying to place them gently on the glass....

So anyway, I've discovered by chance, that certain sizes of PVC plastic pipe caps make good cheap substitutes for cork rings in a pinch, especially for larger flasks that you wouldn't ordinarily have a ring for. A little bit of tape or rubber tubing around the edge helps make it softer and less slippery to the glass.

bbartlog - 19-1-2010 at 07:52

I found it convenient to label most of the glassware (and some other items) in my lab with their weight in grams, and also record the weight of some items that are too small to label. I work almost entirely by weight rather than volume, and this makes it a lot easier to determine the weight of beaker or flask contents without needing to transfer contents or even remove stoppers.

Picric-A - 19-1-2010 at 07:56

Surly if you are working mildly analytically you must consider the wheight of glassware changes considerably with temperature + humidity...

woelen - 19-1-2010 at 09:55

Hmm... weight of glassware changing with temperature? I don't think so. Density may change slightly, but total weight definitely not. Humidity also does not affect the total weight of glassware, unless the air is so humid that droplets of water condense on the glassware, but if that occurs, then it is time to look for another room for experimenting ;)

bbartlog - 19-1-2010 at 10:10

I'm sure there is some adsorption of water on glass (else why bake it beforehand when making an anhydrous setup), but I don't think it's enough to matter to me. If I worked at the microscale instead of with quantities on the order of 100g it might be important.

Picric-A - 19-1-2010 at 11:28

Quote: Originally posted by woelen  
Hmm... weight of glassware changing with temperature? I don't think so. Density may change slightly, but total weight definitely not. Humidity also does not affect the total weight of glassware, unless the air is so humid that droplets of water condense on the glassware, but if that occurs, then it is time to look for another room for experimenting ;)


The temp determines the amount of water absorbed by the glassware, as temperature changes humidity.
And i am sure humity changes wheight of glassware, if not one would not have to bake it before use + dont forget glass is just a less hydroscopic version of silica gel, with varioius other compounds in there.

Panache - 20-1-2010 at 15:23

Quote: Originally posted by bbartlog  
I found it convenient to label most of the glassware (and some other items) in my lab with their weight in grams, and also record the weight of some items that are too small to label. I work almost entirely by weight rather than volume, and this makes it a lot easier to determine the weight of beaker or flask contents without needing to transfer contents or even remove stoppers.


How do you label it though that is impervious to all the conditions it must withstand? engraving works but then you introduce possible stress fractures that cracks can apex off.

[Edited on 20-1-2010 by Panache]

bbartlog - 20-1-2010 at 18:23

I've had to replace scorched tape occasionally, but masking tape and permanent marker (Sharpie) works pretty well for me; good up to about 200C at which point it starts to darken. I suppose some solvents would also wipe it out or disintegrate the adhesive, but I haven't experienced that yet. I suppose if you did a lot of work at higher temperatures that wouldn't be satisfactory, but so far the vast majority of what I've done has involved temps between -10C and ~230C (at least on the upper outside parts of the glass).

DJF90 - 20-1-2010 at 19:36

When you wash the flask doesnt the masking tape come off?!

bbartlog - 20-1-2010 at 20:39

Interestingly, no. The adhesive on the masking tape sticks to glass quite well. Maybe if I ran my glassware through a dishwasher?

aonomus - 20-1-2010 at 21:49

I have found that masking tape on glass bottles and the like stick *very* well, even if you get a bit of solvent on them. The marker might run, but the solvent only loosens the adhesion briefly until it dries out again. You have to soak the tape in solvent and scrape, then use a acetone soaked paper towel to remove all traces of the adhesive if its really old and baked on.

In some other cases, the adhesive does dry out and the tape flakes off, but then that is a different issue.

DJF90 - 20-1-2010 at 22:23

I would have never have guessed! Sharpies are good for temporary annotation of flasks (crude yield, molecular structure (if its to be left on the shelf for some time...) etc. Some flasks (particularly pyrex/duran) have a small white enamel square, which when marked with a pen is very difficult to remove. This could be ideal for recording the weight of your flasks, at least long term if not permanently.

vulture - 21-1-2010 at 14:58

Pencil inside a ground glass joint or on the outside in the white painted square of a piece of glassware holds up to almost anything, except vacuum grease and chromic acid.

Grignards are best initiated by using 1,2-dibromoethane, IMHO.

I have another tip for catalytic hydrogenations with Pd/C. This is often done with a parr apparatus connected to a variation of a Schlenk line, to evacuate the setup and refill with hydrogen. This is done because the H2 can be explosive in combination with Pd and O2. (Usually happens in the student lab sessions :D)

For hydrogenations that don't require large overpressures, I simply use a flask with a magnetic stirrer connected to a three way valve. The other two outlets are connected to a balloon filled with N2 and a water aspirator (or vacuum pump). This allows to remove all oxygen from the setup first by switching between the aspirator and the N2. Once the balloon is drained, it's switched for one with the H2 and the evacuation/purging cycle is repeated. Finally, the vacuum source is disconnected and another balloon of H2 can be connected if necessary.

When reducing small quantities you can dispense of the N2 and go straight to H2. Take care that the flask is filled to no more than 1/3 of it's volume, because of the boiling that can occur during application of the vacuum.

medchem - 22-1-2010 at 08:24

Quote: Originally posted by vulture  
Pencil inside a ground glass joint or on the outside in the white painted square of a piece of glassware holds up to almost anything, except vacuum grease and chromic acid.

Grignards are best initiated by using 1,2-dibromoethane, IMHO.

I have another tip for catalytic hydrogenations with Pd/C. This is often done with a parr apparatus connected to a variation of a Schlenk line, to evacuate the setup and refill with hydrogen. This is done because the H2 can be explosive in combination with Pd and O2. (Usually happens in the student lab sessions :D)

For hydrogenations that don't require large overpressures, I simply use a flask with a magnetic stirrer connected to a three way valve. The other two outlets are connected to a balloon filled with N2 and a water aspirator (or vacuum pump). This allows to remove all oxygen from the setup first by switching between the aspirator and the N2. Once the balloon is drained, it's switched for one with the H2 and the evacuation/purging cycle is repeated. Finally, the vacuum source is disconnected and another balloon of H2 can be connected if necessary.

When reducing small quantities you can dispense of the N2 and go straight to H2. Take care that the flask is filled to no more than 1/3 of it's volume, because of the boiling that can occur during application of the vacuum.


Few months back, I have written a post regarding this procedure with video ...
Check out in detail <a href="http://medchemblog.blogspot.com/2009/11/hydrogenation-demonstration.html">HERE</a>

stir bar retriever

Magpie - 22-1-2010 at 18:56

Finding that I often wish I had one of these but am not willing to pay the $20 + postage, I made one of my own. Here's how:

* Buy 2 feet of 0.17"ID polyethylene tubing ($0.34)
* Buy one 3 foot piece of 1/16" steel rod (~$2)
* Buy one 3/16"OD x 1/2" long cylindrical neodymium magnet ($0.27) (Note 1)

1.Heat about 3/4" of one end of an 18" piece of poly tubing in boiling water to soften it, then force fit the magnet into it, leaving about 1/4" of the end of the tube open.
2. Fuse this end of the poly tube by heating it on a stove, working the end to a seal. Try not to overly heat the magnet as it will lose its magnetism if heated to 80C. (Note 2.)
3. Cut the steel rod to fit in the poly tube leaving about 1/2" of the tube end open.
4. Fuse the open end of the poly tube as before.

Notes
1. The economics are hurt here if you have to pay postage on the magnet like I did. This came to about $5.
2. It might be better to buy an undersize magnet, say 1/8"OD instead. That way you could slide the magnet in later after fusing the end to a seal, and wouldn't have to risk heating the magnet. These Nd magnets are tremendously strong.



stir bar retriever.jpg - 62kB

[Edited on 23-1-2010 by Magpie]

watson.fawkes - 23-1-2010 at 06:54

Quote: Originally posted by Magpie  
2. Fuse this end of the poly tube by heating it on a stove, working the end to a seal. Try not to overly heat the magnet as it will lose its magnetism if heated to 80C.
If you do accidentally heat the magnet above its Curie point, you can remagnetize it by heating it up again and letting it cool off in a magnetic field. A ferromagnet is randomly aligned above its Curie point and an external magnetic field will line them up. As it cools and passes through the Curie point, the magnetic domains lock into place in whatever their alignment is. The strength of the external field doesn't need to be as strong as the magnet itself. The final strength of the magnet is dependent upon its own material properties. All the external field has to do is to get the domains lined up right.

Magpie - 23-1-2010 at 09:42

Thank you watson for that useful information. My heating did cause the magnet to lose much of its strength, although as you can see from the photo, its still plenty strong enough for its intended purpose. At full strength these tiny magnets are supposedly capable of lifting ~1 kg, IIRC.

I did buy a second slightly larger magnet. Are you saying that if I heat the magnet in the retriever up to 80C then let it cool next to this second magnet that I can remagnetize the one in the retriever? Is any special spatial orientation needed? They are both 3/16"OD cylinders. The strong one is 3/4" long.

mr.crow - 23-1-2010 at 20:06

Perhaps you could push the magnet further into the tube, seal it then push it back to the end with a coat hanger.

Stirbars are also magnetic, perhaps an iron nail would also work.

Magpie - 23-1-2010 at 20:15

Quote: Originally posted by mr.crow  
Perhaps you could push the magnet further into the tube, seal it then push it back to the end with a coat hanger.

Stirbars are also magnetic, perhaps an iron nail would also work.


For the 3/16" magnets I bought they are way too tight for that.

I tried to just use the steel rod end out of curiosity, but it didn't provide enough attraction.

watson.fawkes - 24-1-2010 at 07:09

Quote: Originally posted by Magpie  
I did buy a second slightly larger magnet. Are you saying that if I heat the magnet in the retriever up to 80C then let it cool next to this second magnet that I can remagnetize the one in the retriever? Is any special spatial orientation needed?
Yep. The only risk inherent to this procedure as such is that you don't want to heat up your other magnet above the Curie point. So you might want a simple thermal break between the two of them. All other risks about handling small magnets apply, which is why, if you've got an electromagnet around, they're easier to use. If you have a samarium-cobalt magnet, you could use that too, and its Curie point is rather higher.

As for orientation, above the Curie point, the magnetic domains will orient in whatever direction the externally applied field is. So you can choose your orientation as you will, although I imagine axial is what you'll want.

As a small digression, you can get neodymium magnets in rectangular blocks with three different dimensions. These seem ideal for a science demonstration for young children, as you can magnetize them on three different axes and it will immediately visibly apparent that the magnet is now different. Use three magnets and they can handle them together and not rely on their memory. Since it's at boiling water temperatures, it's safe enough for them to participate in the process without undue reliance on safety training.

borosilicate glass stirring rod

Magpie - 26-1-2010 at 16:25

I often need a long stirring rod, something longer than the standard 10" variety, of which I have many. So I end up using my high temperature mercury thermometer as it is quite long. Realizing that this is poor practice I searched for a cheap source for a long stirring rod.

What I found is that you can order Simax borosilicate glass rod in several diameters from art glass suppliers for dirt cheap. You still have to pay the postage, however, which was about $5 for 3ea 20" rods.

Paddywhacker - 26-1-2010 at 20:37

Drying solvents after an aqueous extraction ... you can either stir in your drying agent - some anhydrous salt - or take a glass pasteur pipette, plug the small end with a bit of cotton or glass wool, half-fill with your drying agent, and pass your non-aqueous solvent through like it was a miniature column. The convenience is in handling and glassware usage.

kentkams - 10-2-2010 at 00:33

come to think of it as far as tips go, Id say 2 come to mind and both are POPEYE originals. 1 if u have no running water for distillation or reflux a small to medium bucket and a fish tank water pump (submersible). figure your pumps output to your condensers input via pvc tubing, condensers output with tubing to bucket (use some means to hold your output tube so as to avoid litterally pissing condenser water every where. Extra cooling via ice cubes etc.
second is the vibrator method for non vacuum buchner filtrations, which basicly halves the time of such filtrations, when vacuum sources for whatever reason cannot be easily aquired. Method is to use some form of vibration attached to your funnel (vibrator or as ive used gamepad vibration motor). Sorry if this seems rushed but you get the idea.

Panache - 10-2-2010 at 09:11

if you cannot afford a monomode microwave reactor and like me simply buy the cheapest convential microwave (as i find they only last 6months in the lab) it is worth establishing immediately where the nodes are in the cavity. Convential microwave ovens form a standing wave within the cavity that usually has a maximum (or node) in either 4 or 6 places. I find Sharp microwaves form 4 nodes that seem to correspond to 12, 3, 6 and 9 oclock (assuming your plate is a clock) and the node is halfway between the wall and the center in these postions.
Anyway once you know where the nodes are remove the spinning plate and place your sample to be irradiated directly on the node. If however you require a little less heating and like me you're too lazy to reduce the power (i like the one key start) then simply place your sample away from the node. I find this especially useful for solvents that bump.
Also if you are simply evaporating off a little solvent get a good swirl going in your flask then quickly place it on the node and start.
Another trick for solvents that bump is using a conical flask about four times the volume you need and laying it on its side, when the solvent bumps you get no lose of sample.
Does anyone have a decent method for looking into the microwave that doesn't involve placing your face onto the glass. I get a real shock when the sample bumps.

Oh of course to establish where the nodes are place a plate directly centered in the microwave, with a few mm of water evenly over it and turn the oven on, the water will boil in the nodes first. You naturally have to have the carosel mechanism disabled otherwise this will not work.

rrkss - 10-2-2010 at 10:53

Quote: Originally posted by Magpie  
I often need a long stirring rod, something longer than the standard 10" variety, of which I have many. So I end up using my high temperature mercury thermometer as it is quite long. Realizing that this is poor practice I searched for a cheap source for a long stirring rod.

What I found is that you can order Simax borosilicate glass rod in several diameters from art glass suppliers for dirt cheap. You still have to pay the postage, however, which was about $5 for 3ea 20" rods.


Can you U2U me the supplier, I'm in need of some longer stirring rods.

DJF90 - 10-2-2010 at 11:01

Panache; A more fun way to find out where the nodes are is to scatter mini marshmallows over the "floor" of the microwave (on baking paper, with the carousel plate removed). The marshmallows melt first at the nodes, and give a clearer indication than just evaporation of water. Plus, you can munch the melted marshmallows when you're done :D

Magpie - 10-2-2010 at 11:26

Quote: Originally posted by rrkss  
Quote: Originally posted by Magpie  

What I found is that you can order Simax borosilicate glass rod in several diameters from art glass suppliers for dirt cheap. You still have to pay the postage, however, which was about $5 for 3ea 20" rods.


Can you U2U me the supplier, I'm in need of some longer stirring rods.


My pleasure:

http://www.frantzartglass.com/index.php?main_page=index&...

I first bought a 7mm rod but found it too thick. So I ordered a 5mm rod - it's just right. The rod is 59" long. I had it cut in thirds for shipping.

Panache - 24-2-2010 at 15:41

Not wanting to turn this into a 'Tips and tricks for the home Craft Hobbyists' thread, i will first defend the following post by saying the range of skills useful in a lab are many and varied, especially when the work being performed is diverse.

Epoxies.
Very useful i have found, the following picture is of a b24-b24/b24 claisen head that i dropped resulting in a break on the male ground glass joint. The repair would cost me 5 dollars, however it being the only claisen to b24/b24 I had at the time and the reason i dropped it was it was in use, i needed an instant fix. I epoxied (5 minute araldite) cleanly around the remaining ground glass joint and compresssed it into a b24-b34 adaptor with all of my considerable strength. As it is i have now had the item in use for two years, running through dishwashers cycles at least weekly with not even a yellowing obvious within the joint. I do not use it for refluxing polar solvents (toluene)(mainly because i cannot remember refluxing/distilling anything in a polar solvent lately(but i wouldn't if i was(wouldn't use this part that is(are the brackets confusing anyone yet?)))).
So for those considering what to do with a near broken joint an effective, practical solution would be as just described.
For mixing and applying the epoxy use a polypropylene freezer bag, squirt the 2 part epoxy into the very corner, then mix using the shearing action of the two counter surfaces of the bag, once mixed squeeze the ready to apply epoxy to the corner where a tiny nick will convert your bag into a piping bag.

UnintentionalChaos - 24-2-2010 at 16:12

Quote: Originally posted by Magpie  


My pleasure:

http://www.frantzartglass.com/index.php?main_page=index&...

I first bought a 7mm rod but found it too thick. So I ordered a 5mm rod - it's just right. The rod is 59" long. I had it cut in thirds for shipping.


That's still a bit pricey. I bought 5lbs of 6mm borosilicate glass rod off ebay for chump change. There are a few bubbles, but nothing worth complaining about for the price. I feel like the 6mm is a better size than the 5mm, but that's probably just me.

See here: http://www.sciencemadness.org/talk/viewthread.php?tid=12494#...

Panache - 26-3-2010 at 20:18

Glassware often has little glass hooks welded close to the join. This enables joins to be attached together via the use of small springs. Typically in situations where something is to be left unattended but there may be slight pressure build ups the springs serve as a sort of pressure release valve by allowing the joint to open slightly, depressurise, then snap back.
Unfortunately much glassware is without the hooks (or they face in the wrong direction for your purpose, or one is broken), an easy fix for this is to slide one or two snug but not tightly fitting o-rings over the section just past the ground glass joint, then fit a hose clamp over these and tighten tightly enough to hold the springs.The oring allows for expansion in both the hose clamp and glass and also raises the hose clamp such that it has a lip to hook your springs to.

Skyjumper - 28-3-2010 at 14:00

Store Butyric acid in a double bag to prevent leaks. Trust me /hint

chemrox - 28-3-2010 at 20:04

old fashion glass curtain rods, about 12mm diameter, with expanded ends make nice stirring rods when the need is for a really long one. I picked up a couple of these at the thrifts for a dollar (US). The expanded ends are rough and good for scratching beakers to promote crystallizations.

Panache - 13-4-2010 at 21:01

powder addition is always a pain, the years have not really improved things very much, there's a tricky screw thread type piece of glass which when turned coaxes the powder along a barrel from a small glass hopper, i have never used one of these but they intuitively look too complicated. Normal powder addition funnels (basically a dropping funnel with a ground glass joint at the bottom instead of a tap are just crap.
Anyway a neat way around all this silliness is to use a balloon, fill your powder into the balloon place the balloon over the joint where the addition is meant for. You may then leisurely coax the powder into you system with the fine control of your fingers with no having to constant open the system, if the joint clogs up a bit you can use a gloved hand to squash it down.
Because i'm careful i usually use a double balloon. If your system is particularly aggressive a couple of polypropylene freezer bags within the balloon work well.

UnintentionalChaos - 13-4-2010 at 21:10

As to the above, I have one of the screw-type addition funnels and they are also a pain to use. They work great on small prills or flakes. fluffy powder, not so much. The main problem is that it refuses to move down into the screw assembly and also that you can't really have refluxing solvent or the powder ends up clumping and sticking to the walls.

To solve the not-free-flowing issue, I throw a stirbar into the main chamber and then use a neodymium magnet on the outside to knock powder down into the screw. As for the sticking to the walls, I sure hope you don't need every single grain of the stuff! You might want to try voodoo.

I suspect the bags you speak of are not very vacuum-friendly though, which is no problem for the glass.

Ephoton - 15-4-2010 at 06:50

I have a tip :).

when doing a reflux reaction that then needs distilling afterwards I use a liebig condensor as a fractionating collumn in a distillation setup then connect the output of the distillation condensor to the bottom of the liebig to reflux.

I use two hoses with a glass tube in the middle between the distillation condensor and the liebig.

I then just need to disconnect the distillation condensor from the liebig to stop refluxing and then distill.

this stops the liebig from spilling out over my mantle and stops me from having to crack the system open.

Panache - 16-4-2010 at 05:51

Quote: Originally posted by Ephoton  
I have a tip :).

when doing a reflux reaction that then needs distilling afterwards I use a liebig condensor as a fractionating collumn in a distillation setup then connect the output of the distillation condensor to the bottom of the liebig to reflux.

I use two hoses with a glass tube in the middle between the distillation condensor and the liebig.

I then just need to disconnect the distillation condensor from the liebig to stop refluxing and then distill.

this stops the liebig from spilling out over my mantle and stops me from having to crack the system open.


i must have it wrong in my mind, why not simply use the liebeg as a condenser during reflux and then afterwards turn off the cooling water supply to it before slotting a distillation setup on top of it? This has all the advantages of yourr described method minus the need to use that hose/glass tube return.

Ephoton - 16-4-2010 at 22:14

becouse I dont like unplugging the condensor when its got a mantle under it.

plus I like to have the whole setup put together before I start the way I do it I just need to detach the
two tubes and it changes from reflux to fractional distillation with out me slotting glass together.

the reaction im playing with some times if your not carefull swamps the reflux condensor as well this way
you can not get anything on your mantle it will just in the worst case fill your reciver.

also if you were to do a reaction that gave off nasty fumes and then needed to distill it you can use
the vacuum take off adapter as your gas outlet and lead it to a gas trap. then when you distill you dont
have to brake your system to the air out side. its better this way too for inert atmospheres to I would think.

I do chemistry were I realy should not allow smells to be a problem.

I find the worst smells are when I am chaning setups over from a reaction to a distillation as at these points in time I have very little protection from the vapour given off.

yes I should get my self a fume hood but at the moment I
dont want one were I am.

I dont make smells this way either.


[Edited on 17-4-2010 by Ephoton]

Lambda-Eyde - 10-5-2010 at 01:15

It's probably mentioned all over the forum, but if you have a frozen glass joint, some toluene or similar solvent applied with a pasteur pipette will seep into the joint and allow you to free it up with some force. Remember to apply grease to the joint afterwards if it's a stopcock.
I just did this with an addition funnel that was completely frozen, and it worked wonders.

SWilkin676 - 10-5-2010 at 10:05

Quote: Originally posted by kentkams  
come to think of it as far as tips go, Id say 2 come to mind and both are POPEYE originals. 1 if u have no running water for distillation or reflux a small to medium bucket and a fish tank water pump (submersible). figure your pumps output to your condensers input via pvc tubing, condensers output with tubing to bucket (use some means to hold your output tube so as to avoid litterally pissing condenser water every where. Extra cooling via ice cubes etc.
.

I used a plastic ice chest/cooler and attached hose barbs to the front and a hole in the side for the pump cord. That way the ice stays cold longer and junk doesn't get into the water. To empty I just open the cooler drain outlet into a bucket.

Canning Funnel

SWilkin676 - 10-5-2010 at 10:10

When I'm putting herbals and powders into large wide mouth jars, I had trouble with the stuff sticking - even with a powder funnel. I made a makeshift funnel by cutting the end off a plastic bottle that had a wide mouth to it. Later I found that canning funnels are just what you need - they come in plastic and stainless steel. I also found a neat little gizmo used in canning for lifting lids that is basically a plastic stick with a magnet mounted to the end that works ok for stir bar retrieval (as long as the chemical isn't really nasty).


[Edited on 10-5-2010 by SWilkin676]

franklyn - 21-5-2010 at 06:59

Reflux on a shoestring

Condensor Improvised.gif - 51kB

Melgar - 26-5-2010 at 05:28

Quote: Originally posted by aonomus  
Another thing with gallium is that it wets glass unlike mercury, wouldn't that make it a pain to clean off?

Actually, I have quite a bit of experience with gallium. You can use an alloy of about 70% gallium, 20% indium, and 10% tin to make a metal that's liquid at room temperature. This will alloy with aluminum and expose it to the environment. However, this doesn't work nearly as well with eutectic aluminum alloys, it works much better with pure aluminum. Aluminum foil is fairly pure, but is too thin with too many layers of oxide that need to be eaten through. Aluminum muffin tins are probably the cheapest, best consistent source of pure aluminum I know about.

Also, the gallium alloy can be reused. Dilute HCl or a dilute NaOH solution will make the gallium alloy suddenly ball up on glass. It's actually quite cool to watch. It can then be extracted much easier. If there's a lot of aluminum by-products nearby, they can generally be dissolved by dilute HCl, or even strong HCl for that matter, since even strong HCl doesn't dissolve gallium very fast. The gallium then forms drops on the bottom that do not stick to glass as long as HCl concentration is maintained.

Additionally, the gallium/aluminum mixture can be made a lot more active by melting the two together with a torch first. The only downside is that gallium is expensive. The best I've managed is $2 a gram for 50 grams, and a gram of gallium isn't much. For comparison, silver costs less than half that.

[Edited on 5/26/10 by Melgar]

Chainhit222 - 27-5-2010 at 15:15

I have never seen this done before, but I think it is a useful laboratory technique.
Normally in the distillation of a volatile solvent, you have some losses through the little vacuum nipple on the adapter you use behind the condenser, I notice a design exists for a jacketed adapter (so you can pass water through it like a condenser, I believe I have found an easier solution.

I broke my 105 degree vacuum adapter by accident, but I happened to have a double female 3 way adapter, so I have devised this setup (Used it for ether thus far, seemed to work well)
I attached the Frederich's style condenser to the top female joint of the 3 way adapter (where the thermometer would usually go) and I linked it to my other condenser in series. This way if any liquid vaporizes in the reviving flask, it gets refluxed by the condenser on top of it. I'm not quite sure how effective this method is, or if the losses are even significant through a vacuum nipple, but I believe I have noticed a reduction in odor (when I turn my fume hood off that is).

Picture: http://img179.imageshack.us/img179/4849/ether3.jpg

[Edited on 27-5-2010 by Chainhit222]

Panache - 29-5-2010 at 21:08

Quote: Originally posted by Chainhit222  

Picture: http://img179.imageshack.us/img179/4849/ether3.jpg

[Edited on 27-5-2010 by Chainhit222]


Is that a retort made from a length of steel rod and an old brick? Fantastic! Whats the motor sitting behind the setup for?



11.jpg - 36kB

Panache - 29-5-2010 at 21:10

Quote: Originally posted by Chainhit222  



Picture: http://img179.imageshack.us/img179/4849/ether3.jpg

[Edited on 27-5-2010 by Chainhit222]


Is that a retort made from an old brick and a piece of rod?
Fantastic!

Here's the photo resized lazy dazy hazy.



11.jpg - 36kB

Chainhit222 - 31-5-2010 at 08:58

Retort? From what I understand a retort is this :
http://upload.wikimedia.org/wikipedia/commons/8/84/My_retort...

Are you referring to my ring stand/lab stand I made out of a rock? I took a leftover stone from wall construction, cut it into a cubic shape using a rock-saw, drilled a hole in it, filled the hole with epoxy, drilled a hole a tiny bit smaller then the metal rod diameter in the epoxy, and beat the rod in there with a 10lb dumbbell. I could have just epoxied the rod in there, but I figure this way it is easier to get it to stand up strait.

The other ringstand (round one) was made out of some metal I found in my yard, I drilled a hole in it with a hand drill and used a tap&die set to make it threaded. I find that I prefer my ringstands to the commercial ringstands (which I find to be too light and easy to tip over).

The thing on the bucket in the back is a condenser pump. I am going to replace it with a nice quiet aquarium pump though.

[Edited on 31-5-2010 by Chainhit222]

Panache - 4-6-2010 at 08:22

sry meant retort stand not retort, lumps of lead work well as bases also, i agree with you about commercial ones being flimsy and flexible.

filtering cold crystals

Panache - 4-7-2010 at 00:24

Often when one is filtering fine precipitates or crystals from cold solutions one has kept dry it is typical to cover the buchner funnel with a flexible cover that essentially gets vacuum sucked down ontop of the filter cake, this aids also in compressing the filter cake and speeding the filtration.
Annoyingly though when one takes the filter cake out as it is very cold it will immediately condense water onto it surface. this is especially true for fine precipitates. As such it is worthwhile to leave the filtration running until the cake has returned to ambient temperature but this can take some time and in the interim water can leak into your system anyway.
Using a heat gun ontop of the cake can sometimes work effectively but is also slow as one needs to keep the temperature of the gun just above ambient, othewise one can volatilise the remaining solvent and problems ensue.
A good trick is to double up a balloon then fill it with enough water to make a sphere around the size of your buchner. This can then be microwaved to warm it slightly. it is then placed ontop of the filter cake, this gently but quickly warms the cold filtrate in a very controlled manner.

spong - 19-8-2010 at 00:55

If you're distilling something that would usually attack the rubber seals on ordinary thermometer adapters, instead of getting fancy ground glass thermometers or a teflon adapter, the thermometer can first have one layer of teflon tape wrapped around it, the oring rolled down on top of it and then another layer of teflon stretched over the top. Then just poke it down into the adapter and thread the cap on top, sealing the teflon against the glass.
It's also handy for bubbling gasses into flasks, just work out the length for a bit of 6mm boro tube to reach the base of the flask first.

aonomus - 28-9-2010 at 14:47

This thread needs a bump.

In case anyone didn't know, if you find your oil baths stratifying and giving slow heating, bending a paperclip and placing it in the bottom of the oil bath with a magnetic stirrer is a great way to stir your oil bath, without dedicating a expensive stir bar to the task.

psychokinetic - 29-9-2010 at 12:08

Potentially stupid question time: Are the stir bars often single use?
(I'd put this in the short questions, but it relates directly to your tip.)

[Edited on 29-9-2010 by psychokinetic]

aonomus - 29-9-2010 at 15:09

Stir bars are not single use, however sometimes if you leave a stir bar in an oil bath stirring, for ages and ages, when you really want to use it you will find the teflon worn out and down to the magnet in spots.

Contrary to popular belief, teflon stir bars are not invulnerable to mechanical wear.

Another slight problem is the potential for the heating oil to contaminate future reactions if the stir bar is very pitted, and you have done an insufficient job at cleaning it; silicon oil is very hard to remove even using hexanes or MTBE. Beyond that, there is all the *other* crud that you find in oil baths that make it brown/black. I would rather stick my finger into most of my reaction mixtures because I *know* what is in there, vs an oil bath used by an unknown number of people, with an unknown variety of chemicals.

psychokinetic - 29-9-2010 at 23:51

That makes a lot of sense. I've seen what people do to oil baths.

Panache - 17-6-2011 at 16:50

These two photographed products are used for a 'dip' style rubberised coating for tools and the like, whilst very useful for rubberising the handles of shanks to help you get a good grip whilst murdering inmates they can be used in the displayed style to produce an anti slip 'tread' on concrete or coated concrete or timber.
I used the 80's random swirl pattern, using black and yellow pants on a matt black pigment and silicon oil coated floor because i'm lazy and it required little planning, but the results, SPECTACULAR!!!!


Likewise when thinned down a little they are an excellent coating on lab benches, i would have displayed a photo of mine however it just look like a black bench. I applied it selectively so i have 'zones' without the coating so super hot things can still be placed somewhere.
Also i realised i haven't waffled on yet about my dazzling innovation for uncoated concrete floors, the paving paints made for them are only really decent if considerable effort in gone into preping the floor, otherwise the coating will readily lift. So you're talking a bout a major effort mopping, hcl treatment, maybe some grinding, further mopping, removing everything blah blah...However leaving them uncoated means concrete dust, yucvk!!!
Wow this is sounding like an ad. Anyway if you buy some raw tint from the paint shop, its just staining pigment, the pigment in a minimum of alcoohol, dilute this down by half and slop it on the floor and brush it around with a broom, trying to get an even coating, or not depending on your laziness, after this the alcohol quickly dries, like in 2min. You then squirt a minimum quantity silicon oil (from the bath not new stuff!!!) and rub this around with a broom (not the same one), coating evenly. This effectively coats the pugment (thats NZ for pigment) and the floor, Voila, a surface treatment for the lab in under ten minutes. it need reapplying now and then, yearly or so.

I use the same treatment for my timber benchtops, using more silicon oil however.

Second tip of the day relates to explaining the dangers of certain chemicals to others. Say if you've explained that NaOH in ethanol/water is very aggresive to cells even cf NaOH in water as it migrates the caustics readily into the cells, always wear the full gamit of elbow high thick nitrile gloves, face shield long sleeves, boots blah blah. The tip for others is to never assume that a somber and well intended warning/training, such as this, will stop someone from being an idiot.

That perhaps harsh, i do feel very badly for someone that i had to sit in emergency with last week whilst their second degree considerable caustically mangled forearm, wrists and hands where peeled of some of their epidermis and all hair. it was a close call it could have ben so much worse had i used the concentration of NaOH i would have used. The reality is it's my fault, they were working for me, they got hurt. I considered my training and supervision more than adequate, bordering on the paranoid, it wasn't.

The problem was all my warnings, training and ernest advice on this chemical was not sufficient for them to infer that if you get it on your skin wash it off immediately. Their gloves quickly filled with a combination of this cleaner and spray water and the such, but they continued to work because it didn't hurt, so they thought it must only be water, luckily they had tight nitrile gloves on under the heavy pair of elbow length ones which stopped the wholesale burning of their hands, forearms and wrists not so, ugly deep red scarring. It makes you feel like a monster when something like this happens.


Anyway thats it for today.


edit fucked if i know whats up with the photo uploading, probably my wicked photoshops skillzzzzzzz. anyway no photo of te floor sorry. also no spell checking be3cause i wastede too much tiome trying to get the photo uploaded.

ScienceHideout - 18-6-2011 at 07:08

My tip:

Close the stopcock before you pour something into a sep funnel! It's happened to be a dozen times...

Panache - 20-6-2011 at 18:33

Quote: Originally posted by ScienceHideout  
My tip:

Close the stopcock before you pour something into a sep funnel! It's happened to be a dozen times...


and it never stops happening IMHO (except it you cease using sep funnels altogether), however the frequency decrease significantly.

A good habit to get into is to make sure you always have a vessel underneath the funnel beorehand, this way you have to forget two things in order for a problem to occur, which is less likely i find.

GreenD - 21-6-2011 at 14:36

my TA showed me this one;

When running a column, most often people are taught to continuously exchange out test tubes of the filtrates, until TLC analysis shows a change. Often this is cumbersome to stop, tlc, analyze, etc, so often it is also the case that people run dozens of test tubes, possibly reaching near the hundreds.

Instead of then dotting each test tube on a tlc plate and looking for seperation, simply make a grid on the TLC plate, such that from left to right and top to bottom is numbered (in your head) 1-n of your #n test tubes. Then simply spot the little squares, one for each test tube, and immidiately test under UV. This quickly shows which test tubes are completely empty of product and can be ignored, and zeros in on the possible tubes to be analyzed.

Saves time & plates. Hope that was easy to understand :)

DJF90 - 21-6-2011 at 14:44

Obviously that method is flawed for a number of reasons. The first is that not all compounds you are trying to separate may be UV active, either at 254nm or 356nm (blacklight). The second is that if one of the fractions contains two compounds (i.e. that either co-elute or are very close Rf values) then your method will not show the presence of two compounds - you will only see one fluorescent spot. An improved method would be to shine UV on the fractions themselves whilst still in the test tubes - fluorescence will be noted and you'll save on the TLC plate, but you're still going to suffer from the same drawbacks.

GreenD - 21-6-2011 at 14:53

I don't think you understood - it isn't a miracle cure for anything, it just saves you the time of making 10 TLC plates for 50 tubes (5 spots on each plate).

Once you know which one's are active (assuming you know that your compound is UV active), then you continue as usual, eliminating (hopefully) a large portion of them.

Shining UV on test tubes alone requires complete darkness, and if that is available, then yes - that is probably the better result. However, if your compound degrades under UV light (short wave) you may want to consider only doing spots.

Dr.Bob - 21-6-2011 at 20:02

A few tips from my experience:

1) A sand bath works very well for heating round bottoms and other items on a hot plate. Put the sand in a metal pot, crystallizing dish or even in heavy aluminum foil. This works best when you need to heat something at a high temperature for a long time at reflux. Not as good for distillations or low temps.

2) If you can get one or two long Vigreux columns, it will work well for an air condenser in many cases for refluxing solvents, thus saving water or other coolants. If you are trying to disconnect Tygon tubing from a condenser, cut it off and slit it. I have broken several inlets off trying to remove Tygon. To put Tygon on, use a little acetone to swell the tubing for a moment and it will slide right on.

3) When filtering a very wet solid, I was taught to put a thin rubber glove over it and let the suction pull it tight. It will squeeze the liquid right out of the solids in many cases.

4) To look for non-UV active compounds, take a gram of iodine and place it in 50-100 mls of silica gel in a bottle big enough to hold your TLC plate. Mix well, and the iodine will saturate the silica. Then place a dry TLC plate in the bottle, turn it until the silica is spread on the plate and let it sit for a few minutes. This will show spots much faster than just solid iodine in a bottle.

Bob

ziqquratu - 21-6-2011 at 20:04

DJF90, the idea of shining UV light on the tubes directly will rarely work - when we run TLC, the fluorescent compound is pre-bound to the silica itself (from memory, the most common one is some zinc compound), and the spots we observe under UV light arise through the compounds of interest QUENCHING that fluorescence. Not many compounds fluoresce themselves when exposed to UV light. You can actually see the difference when you DO have a fluorescent sample on a TLC plate - rather than the usual dark purple spot, you observe a glowing spot of whatever colour - purple, blue, green, red, it depends on the compound.

GreenD, your method can be expanded to use stains as well, for compounds which are UV inactive. You can either stain the whole grid once you collect the number of tubes you expect you'll need, or you can in fact just spot a little of the stain onto each grid square after you spot the sample. It's not as effective as UV, and the spotting method is almost worthless if you have to heat to see a colour change, but it can work OK for stains like KMnO4.

The best part about GreenD's method is that you don't have to stuff around preparing a proper TLC plate while running a column. If you're running a flash column, you need to switch tubes every 30 sec or so. Trying to spot each fraction in that time can be tricky, particularly if you insist on nice, tight spots. But doing this, you can have big spots - which are quick to do - on your "screening" plate, then go back and just do the fractions with something in them (plus one or two either side) carefully, saving a lot of effort. Plus, you know immediately when your compound has finished eluting, meaning you can save time, tubes and solvent.

DJF90 - 22-6-2011 at 10:04

I agree that in many cases the indication of product is due to quenching of fluorescence on the plate by the compound - the plate itself is sensitive to the 254nm light and fluoresces green. Where fluorescence is quenched (i.e. where there is product), the plate appears violet-purple in colour, due to the longer wavelengths emitted by the bulb. You are right that not many compounds actually fluoresce themselves though, but there are many cases where this occurs, typically in PAH's. Sometimes a products colour may allow easy identification - compounds with extended pi systems are typical candidates, such as chromones, which are typically in the yellow region (and azulene (blue), which also shows fluorescence - its actually a special case in which fluorescence occurs from S2, not S1, due to a conical intersection between the S1 and S0 levels allowing instantaneous relaxation without emission).

Staining is a good method once UV has been tried, but there are instances where a single stain will not show all the compounds (some common "universal" stains are p-anisaldehyde, ceric ammonium molybdate and phosphomolybdic acid). If you're only interested in your product, then you may be able to identify it by a functional group selective stain, depending on what your possible side-products are.

peach - 16-7-2011 at 19:40

Quote: Originally posted by Panache  

1.Low boiling solvents (dcm, ether, acetone etc) are excellent for their ease of distilling but are a pain for doing vacuum filtrations with as the solvent can easily boil in the flask, or worse still in the filter. To circumvent this when filtering low boiling solvents i pull a full vacuum on a round bottom of appropriate size, tap it, then use this a the vacuum source and filter flask. The solvent then has nowhere to go if it boils.
Useful for this technique are some decent taps with groundglass sockets each side. I have a wizz bang 15mm bore, 34/35, vacuum tap i use for this now but initially i used vacuum tubing, less elegant but completely servicable.


I've had this problem as well, and found it helpful to first cool the collecting flask in the freezer. With it on super freeze, it'll come out at about -30C. I wrap in a towel to keep it cool. The solvent attempting to boil in the collecting flask will only cool it further. Provided the flask is already cold, and insulated, it will quickly run out of energy to boil, if it had enough on entering the flask; which is now effectively a trap it's laid for it's self.



Conversely, I have had the opposite problem at the filter elements themselves. When dealing with fine particulates and low boiling solvents, the paper will start clogging a little, then the vacuum below will increase, then the solvent will boil lower and help freeze the funnel some more until the filtration stops dead. Giving the element a warm with some hot air can make a massive difference to filtration times in these instances; minutes versus hours.
Quote: Originally posted by kentkams  
Method is to use some form of vibration attached to your funnel (vibrator or as ive used gamepad vibration motor).


Yep.

I've done this too.

Another example of where it can help is when dealing with bubbles that sit around the phase boundary in a sep funnel. Putting something that vibrates against the glass helps them shimmy into place and burst into their own side of the boundary. I thought of this when I found myself tapping on the side of the funnel with my fingers all the time to knock the lower layer drops that are stuck on the wall in the top layer back down.

It also works to settle some precipitates.

Going back to filtration, one of the best ways to speed it up is to wait for the precipitate to settle by gravity and then remove the top layer first and only pour in the precipitate as the transfer media (ex solvent) is running out. Sometimes the precipitates clump and sit suspended rather than falling. A quick buzz with a vibrator of some description and they immediately collapse to the floor.

I have used electric toothbrushes and the Gillette Mach 3 before now, as well as a sex toy. I would recommend the latter as they are variable, more powerful and soft, so they won't chip the glass. Finding the right spot can take a minute, and it is not always in exactly the same place.

I'll preemptively get in with a, "That's what SHE said!".

[Edited on 17-7-2011 by peach]

Magpie - 17-7-2011 at 07:26

I found that while removing some normally slimy CaSO4 by vacuum filtration the addition of some CaCO3 made the filtration go quite smoothly.

Panache - 6-10-2011 at 04:41

Placing an inverted plastic disposable pipette into your wash bottle instead of the tube allows for longer use upside when squirting up into a flask or whatever, conversely you could have two bottles for each solvent, one with the tube removed and use exclusively upside down.
Obviously the pipette needs to be pierced at the bulb.

[Edited on 6-10-2011 by Panache]

ScienceHideout - 6-10-2011 at 13:25

Don't pipette by mouth.

Magpie - 7-3-2012 at 10:53

Do you ever get frustrated trying to force the stiff rubber vacuum hose onto the tublature of your Buchner funnel? I often did and was concerned that I was going to break the tublature and cut myself badly. Here's a convenient solution:



Buchner funnels.JPG - 128kB

bfesser - 7-3-2012 at 16:30

I put some quick disconnects from <a href="http://www.colder.com/" target="_blank">CPC</a> on my rotavap condenser for similar reasons. I found them for 25&cent; a piece at a <a href="http://www.ax-man.com/" target="_blank">local surplus shop</a>, so I bought all they had.

[Edited on 3/8/12 by bfesser]

Mailinmypocket - 12-4-2012 at 11:09

I bought some pipe cleaners to play with my cat... Good times!

I discovered they are the most awesome thing to clean and scrub the inside of droppers, pasteur pipettes, droppers etc! (they are small pipes I suppose so a pipe cleaner sounds like the obvious choice lol)

They work especially good for removing strong dyes and oily reagents from your small glass and even plastic tubes. Lots of you probably use them all the time but I just thought I'd share!
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