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sselinger
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[*] posted on 2-3-2015 at 20:56
my lab instructor...


This is a while back...we were using nabh4 to reduce something. Sensitive to water. We were given magnetic stir bars, I decided to give it a rinse with water to rid of impurities then dried it up with a paper towel. I want to do this since last lab we had poor results due to impurities because our glassware is shit.
My lab instructor says I shouldn't do that and gives me a new one. Now at this point I am fuming and i can feel the vein in my neck blowing up and swelling out of anger. I yelled at her and told her I can easily dry it and get a better purer product. Who is right? I'm pretty sure it's easy to fully dry a little magnetic stir bar...
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Bert
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2-3-2015 at 22:47
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[*] posted on 2-3-2015 at 23:55


Your glassware is shit and for this reason you have to clean the stir bars?

Of course you can rinse them and dry them afterwards, but if they are really dirty, then you need to clean them with more than water. Maybe you need some oxidizing acid mix for cleaning the bars (and glassware).




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Sulaiman
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[*] posted on 3-3-2015 at 02:49


From my memory of school chemistry, there are time constraints,
so thorough drying is difficult, and if water could cause problems
such as reacting (potentially violently) with one of the components
I can see why the lab instructor was cautious.
After washing rinse with acetone, alcohol or similar water miscible volatile liquid for rapid drying.
BUT introducing ANY chemical, (water, alcohol,acetone etc,) may cause unforeseen reactions,
so unless you can reliably predict all possible outcomes, it is wiser to ask before changing a procedure.
(you do not have enough experience to predict all possible outcomes,
I know that I do not and I doubt that your lab supervisor does either)

Also, there may have been a bit of an ego problem, you were implying that the lab staff were not doing a good job.

So, follow procedures EXACTLY unless you have prior approval.

Nowadays avoiding liabilities is much more important than stimulating students, an unavoidable societal problem, live with it.

At school in the '60s I did A-level chemistry, 16/17 years old, I ran a lunchtime chemistry club unsupervised
and I was given the keys to the chemicals and equipment storage room, not much chance of that happening today.
I was lucky, although my school was a local government school we had lots of facilities,
the decades of underinvestment in education here in UK means that children now get a poorer education than I had.
I have so many criticisms of the present school system that I shall stop here before I burst into a ranting rage.

[Edited on 3-3-2015 by Sulaiman]
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Zombie
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[*] posted on 3-3-2015 at 04:58


I have read there are time constraints as already said.

Everyone gets your point but you have to come to grips w/ a couple facts...
You are still learning
Teach, runs the class

Graduate, become the Dean, and fire the teacher. Till then, learn to play nicely with others, and do as you are told. (bring enough for everyone if you brought some for you) Just a bonus rule...




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Magpie
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[*] posted on 3-3-2015 at 10:23


Quote: Originally posted by Sulaiman  

I was lucky, although my school was a local government school we had lots of facilities,
the decades of underinvestment in education here in UK means that children now get a poorer education than I had.
[Edited on 3-3-2015 by Sulaiman]


The '60s curriculum for my BSChE included a 3 credit course in organic chemistry. There was a higher level 5-credit course for chemistry, pharmacy, and pre-med majors. But the course I took was comphrehensive and adequate for my major. In the lab every assignment was a synthesis. Some used agressive chemicals like elemental Na, PCl3, and acetyl chloride.

I sometimes travel through my university city. When there I often stop at the Starbucks/bookstore on campus. While enjoying my latte I visit the chemistry section to see what the current organic lab manual looks like. On my last inspection I found that it had no syntheses! Every assignment was just a few qualitative tests. :(




The single most important condition for a successful synthesis is good mixing - Nicodem
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Etaoin Shrdlu
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[*] posted on 3-3-2015 at 10:52


It is possible that is an OChem I manual. Usually there are syntheses in the second semester. At least, that was how it was at my university.

I was also quite disappointed that we spent half a year on technique instead of doing interesting things.
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[*] posted on 3-3-2015 at 13:32


If you Assume you know best, and somebody regarded as knowing more than you says 'Do it Like This' and it angers you, the ONLY reason is that you know shit, yet think you know it all.

The real danger of this state of mind is that if you're becoming arrogant, you are no longer Learning much at all.

You need to Learn how to Learn before you can ever possibly become the Master of anything.

Edit:

as for the stirbar, what was your genius plan to rid it of all it's water, how long would that take, and can you show mathematically how your stirbar would have been drier than the new one ?

[Edited on 3-3-2015 by aga]

[Edited on 3-3-2015 by aga]




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[*] posted on 3-3-2015 at 14:55


Quote:

"You need to Learn how to Learn before you can ever possibly become the Master of anything."


Perhaps the quintessential Science Madness lesson.

The common thread that binds this site (IMHO), is the fact that almost all of you ranking members point out how important it is to learn HOW to learn.

Respect!




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Magpie
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[*] posted on 3-3-2015 at 17:27


Quote: Originally posted by Etaoin Shrdlu  
It is possible that is an OChem I manual. Usually there are syntheses in the second semester. At least, that was how it was at my university.

I was also quite disappointed that we spent half a year on technique instead of doing interesting things.


It was a home-grown O-chem manual of sorts. To be fair my visit was late in the semester and I saw no other O-chem manuals for any higher level courses. It is also possible that this was for "o-chem lite" for nurses, foresters, wildlife, etc, majors, not science/engineering/medical majors.

On the good news side my local community college has an excellent O-chem course. There are 2 ea 3-hr labs/wk. The first qtr deals with technique (mps, distillations, etc). The 2nd qtr is all synthesis, and the 3rd qtr is syntheses/analytical instrument usage (gc, ftir, gc/mass spec). This excellent program is due to the old-school dept head who understands and is able to defend this rigorous course from those nipping at her heels (admin boss, OSHA, EPA, etc).




The single most important condition for a successful synthesis is good mixing - Nicodem
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sselinger
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[*] posted on 3-3-2015 at 22:05


Quote: Originally posted by aga  
If you Assume you know best, and somebody regarded as knowing more than you says 'Do it Like This' and it angers you, the ONLY reason is that you know shit, yet think you know it all.

The real danger of this state of mind is that if you're becoming arrogant, you are no longer Learning much at all.

You need to Learn how to Learn before you can ever possibly become the Master of anything.

Edit:

as for the stirbar, what was your genius plan to rid it of all it's water, how long would that take, and can you show mathematically how your stirbar would have been drier than the new one ?

[Edited on 3-3-2015 by aga]

[Edited on 3-3-2015 by aga]


alright maybe i was overreacting...

BUT Look at the situation objectively. Is it a bad idea to clean the magnetic stir bars and dry them VS just picking up a used one? Which one really is cleaner and safer?
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[*] posted on 4-3-2015 at 03:25


Well, first of all NaBH4 is not all that sensitive to water, the reaction is reasonably slow. For example there are many reported borohydride reductions done in aqueous conditions at around 0 °C. So a little moisture would not hurt this reaction as there's usually borohydride in excess to start with. Secondly, if dry glassware is needed fast 1. rinse with acetone/ethanol 2. dry with air 3. keep in oven for few minutes. Stirbars can also be very efficiently cleaned with tissue paper as you did. There's of course the issue of if water even dissolves the compounds that could interfere with your reaction..

[Edited on 4-3-2015 by kavu]
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