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Author: Subject: Laboratory Tips and Tricks
Panache
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[*] posted on 20-12-2009 at 23:28
Laboratory Tips and Tricks


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!




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[*] posted on 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]




What a fine day for chemistry this is.
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[*] posted on 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.





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aonomus
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[*] posted on 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]
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UnintentionalChaos
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[*] posted on 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]




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[*] posted on 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]




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aonomus
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[*] posted on 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...
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Panache
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[*] posted on 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.




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[*] posted on 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.
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Panache
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[*] posted on 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.



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[*] posted on 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).



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[*] posted on 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.
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[*] posted on 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.




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[*] posted on 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]
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[*] posted on 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.
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[*] posted on 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.
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[*] posted on 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?
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[*] posted on 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.
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[*] posted on 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.




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[*] posted on 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?
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[*] posted on 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.



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[*] posted on 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]
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[*] posted on 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.
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[*] posted on 27-12-2009 at 06:43


^ Yes, I think that is used as a nicer form of Br2 (the ethene goes)
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[*] posted on 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?
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