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jgourlay
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PTFE or Glass Stopcocked titration burette?
Gents,
I want to buy 1 (one!) titration burette. I know someday I'll want to noodle around with nitric acid. Is the PTFE stopcock okay, or do I need the
all glass kind?
I've heard the all glass kind tend to freeze up and have other problems.
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jokull
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Hi!
Maybe you'll find useful to review the specifications from the manufacturer. However, nitric acid is sold in glass bottles (so make your conclusion)
and how agressive a reagent can be depends on concentration.
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Barium
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PTFE is ok for nitric acid.
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Picric-A
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Yep PTFE is ok with with almost everything, but of course long storage in contact with corrosives will cause it to deterioate (sp?) keep PTFE away
form strong hot alkalis and it will be fine.
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panziandi
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Take your PTFE stopcock out of the socket for storing or loosen it as an overtightened PTFE stopcock can expand and break the glass socket. This is
because the teflon and glass have different thermal expansions. Otherwise, no issues with the PTFE its great, and will be fine with the HNO3.
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DJF90
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On the question of burettes, what are peoples oppinions on the ones manufactured from amber glass? If you could have just one burette, would it be
amber or normal, and what volume would you choose? Reasons?
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undead_alchemist
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Many amber burettes started out as clear ones, just stained and finished in the standard process for clear.
Also are you wanting a Class A, or Class B grade one?
You are also forgetting about the screw type stopcocks, they are very smooth working.
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jgourlay
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Undead:
As to "A" or "B", I want the one I will cry over least when an absent minded adolescent knocks it over with his elbow onto a concrete floor.
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Klute
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Amber burettes are mostly used for certain photo-sensitive reagents (AgNO3), etc and are not really common, in my experience.. You would better be
off with a colorless one, easier reading, and you can easily see how clean it is.
25mL is a very well suited size IMO, nice for 50-100mL erlens etc
10mL could be suitable too, but better use only half or 1/4 the capacity, than to fill the burette during a titration. Depends on the precision you
are looking for I guess.
Microburettes are needed only in certain specialized titrations, and most of the time their precision is mucher higher than most needs. Much less
practical, and not worth the money to have one at home IMO. You can just use your 25mL burette with more dilute solutions...
I have always seen PTFE stopcocks on burettes, and never encountered any problems on that side. I suppose glass stopcocks would require grease, which
might be more problematic with things like HNO3 than PTFE.
BTW, you don't plan on doing titrations with conc. HNO3 do you? That would give very imprecise results....
[Edited on 19-9-2008 by Klute]
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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undead_alchemist
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Micro-Burettes, like 1ml, 2ml, 5ml. are very thin.
The other day, I was looking over a 1ml burette sample that we got in, and it was knocked over on the table and broke. 
Lesson: Leave them in the box or storage drawer until use.
Was able to save the stopcock and the funnel half.
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bfesser
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I would recommend PTFE, but not a rotoflo type valve, just a standard PTFE stopcock--you can't give quick half-drops with the latter. I often find
that 50 mL is too large for my needs, and plan to get a 25 mL, but I mostly use microscale techniques and kit. Class A is nice, but Class B is
cheaper and fine for most amateur use.
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Klute
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What is class A and class B? The quality of the glass? A surface treatment?
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
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DJF90
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Isn't it something to do with the precision/accuracy of the markings?
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panziandi
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I'm sure the Class rating is to do with the accuracy. Not sure but A tends to say +/- so many mL @ a cartain temperature whereas I think Class B may
just say +/- and a larger degree of inaccuracy. But either way, Class B is suitable for most work, especially crude or amature work. Class A is sort
of for the more analytical precission, but it's not worth it if the reagents are also not highly pure and highly accurate, and if the chemist uis not
skilled enough, or else the errors will make it more justifiable to use Class B...
The Spring type mentioned above somewhere... these are nice and very smooth and very reliable, I have a couple of such burettes.
25mL is ideal! or even a 10mL can be handy. I have a few micro ones... but these are generally quite useless!
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bfesser
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If you're really interested in the subject, pick up a good analytical chemistry book, but class B glassware generally has tolerances twice as large as
those of class A. I'm always a little bit disappointed that there aren't many people into analytical chemistry on this forum--granted it's not the
easiest for the home lab amateur.
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Klute
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Let's say that analytical chemistry is more of a "tool" for many, and not as passioanting as organic chemisty, or preparative inorganic chemistry.
But it is a very broad aspect of chemistry, with lots of interesting reactions and and sometimes complex relationships.
Unfortunaly, a large amount of titrations requires precise and/or expensive equipements (electrodes, pH meters, conducivity cell, etc), very pur
reagents and specific training/skills, that only few people here can afford/have. Precise titrations are needed in professional settings, but rarely
for amateurs. But it is true analytical chemistry can be used is many "improvised" ways at home to determine yields, quality of reagents, etc
EDIT: I've done a fair share of analytical chemistry in school and in a QC lab, but never heard of class A et class B burettes... Maybe it's simply a
different term in europe, or it's just that the places I worked in only ha dthe one type (0.025mL gradautions generally).
[Edited on 21-9-2008 by Klute]
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
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not_important
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Class A is generally tested as to the accuracy and that calibration is marked on the burette or flask; they may be certified as to their accuracy.
Some manufactures give the units serial numbers and retain the calibration information. Class B is of wider tolerance and are "generic", no
certification, individual calibration indications, or tracking; it's also much more affordable while class A would be used for applications linked to
official analytical requirements.
The terminology is fairly widely used, see the following for an example.
http://www.hecht-assistent.de/e_glass_instruments/automatic_...
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undead_alchemist
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Also please note, not all class A/B items are the same.
For North America you have ASTM for the references. For the rest of the world, they use DIN.
ASTM Class is is higher tolerance then DIN Class A.
Example 100ml Volumetric Flask. for ASTM it is 0.08ml for DIN it is 0.1
So for the most part I count DIN Class A glass as Class B ASTM.
[Edited on 21-9-2008 by undead_alchemist]
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Klute
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Are you saying your burettes are better than ours?   Let's have a titration competition  
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
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panziandi
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I have seen cheap acrylic burettes with ptfe stopcocks. This is a viable option for colleges etc, perhaps useful for amatures where high precission is
not always neccessary or affordable.
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jgourlay
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Thanks for the answers gents. I'll be doing, I suppose, a lot of analytical chemistry. This isn't really a hobby for me, at least that's what I tell
the wife and I'm sticking to it! This is all an adjunct of homeschooling. I expect analytical to be a big part of it because I want them to do a lot
of "pour boiling through dirt...now, tell me what's dissolved in the water", etc.
I may be wrong, but it strikes me that analytical chemistry is a litmus test (har har har!!) for whether you really understand chemistry.
As with many fields, one has to have some expertise, sometimes great expertise, to do the modern work. But very few modern professional settings
require the depth and breadth of knowledge one has to have to replicate, for example, the technologies between 1750 and 1940 starting with the same
raw materials.
Analytical chemistry smells to me much like engine building--and many supposedly "good" engineers have foundered on the rock of trying to make "hobby"
engines in their home garage.
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ScienceSquirrel
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The major problem for analytical chemistry at home is getting chemicals that are sufficently pure to act as a primary standard and then weighing them
out accurately enough.
Making ferric alum etc at home is quite easy as a balance that is accurate to 0.1g and adequate for preparative chemistry on say a 10g scale is easily
and cheaply obtained.
A balance that is adequate for analytical chemistry is a lot harder to obtain and maintain.
Also there is a lot of work involved in preparing and maintaining the primary and secondary standards.
I once worked in a place that trained pharmacists and a lot of the old British Pharmacopeia stuff was worked through to give the students experience
and an insight into chemistry.
A lot of technician time was spent making and standardising solutions.
Gravimetric analysis for say soluble sulphate in soil by extracting with water, acidifying and then precipitating the sulphate as barium sulphate is
time consuming and more than a little tedious.
I would do the work if someone paid me but I can't see me filling up a Saturday afternoon with this sort of stuff.
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jgourlay
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Squirrel---you make it sound so appetizing!
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ScienceSquirrel
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You can get hold of vials that when added to a certain amount of deionised water in a volumetric flask will produce a solution of say 0.1M
hydrochloric acid.
That is a cheap way in to accurate volumetric work on a limited scale.
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jgourlay
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Sqirrel: where do you order those?
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