jgourlay - 19-9-2008 at 11:32
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.
jokull - 19-9-2008 at 11:47
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.
Barium - 19-9-2008 at 11:57
PTFE is ok for nitric acid.
Picric-A - 19-9-2008 at 12:04
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.
panziandi - 19-9-2008 at 12:14
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.
DJF90 - 19-9-2008 at 12:24
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?
undead_alchemist - 19-9-2008 at 13:00
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.
jgourlay - 19-9-2008 at 13:03
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.
Klute - 19-9-2008 at 13:41
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]
undead_alchemist - 19-9-2008 at 18:40
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.
bfesser - 19-9-2008 at 19:26
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.
Klute - 20-9-2008 at 06:53
What is class A and class B? The quality of the glass? A surface treatment?
DJF90 - 20-9-2008 at 11:23
Isn't it something to do with the precision/accuracy of the markings?
panziandi - 20-9-2008 at 13:49
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!
bfesser - 20-9-2008 at 17:17
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.
Klute - 20-9-2008 at 17:40
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]
not_important - 20-9-2008 at 18:04
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_...
undead_alchemist - 21-9-2008 at 02:01
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]
Klute - 21-9-2008 at 03:55
Are you saying your burettes are better than ours? 
Let's have a titration competition 
panziandi - 22-9-2008 at 02:42
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.
jgourlay - 22-9-2008 at 04:50
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.
ScienceSquirrel - 22-9-2008 at 09:32
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.
jgourlay - 22-9-2008 at 13:57
Squirrel---you make it sound so appetizing!
ScienceSquirrel - 22-9-2008 at 17:46
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.
jgourlay - 23-9-2008 at 04:48
Sqirrel: where do you order those?
ScienceSquirrel - 23-9-2008 at 05:15
BDH do the Convol range
http://uk.vwr.com/app/Header?tmpl=/product_range/chemical_re...
I doubt that you will be able to deal with them directly but someone like a school may be able to order for you.
You are going to need quite a bit of glass as well; burette, a few pipettes and some volumetric flasks etc so look around and find a local supplier
willing to deal with you
jgourlay - 23-9-2008 at 06:11
Now isn't that slick!
I need to start a little company just for the purpose of dealing with all the folks who only deal with companies.
ScienceSquirrel - 23-9-2008 at 08:11
Sodium bicarbonate BP or USP is readily available and very pure.
Heating it to constant weight yields very pure sodium carbonate which would be an effective primary standard.
If you can get a set of scales that are accurate to say 0.01g or better 0.001g that would give you results in an acid base titration that would be
accurate to ca 0.75 or 0.075% respectively working on a 25mM scale.
There will be other sources of errors, eg your technique, I assume that you have not been formally trained, and the purity of your deionised water.
If you can obtain hydrochloric acid or sulphuric acid in a good grade then you can standardise them against your sodium carbonate.
You will not be able to do anything great. But you will be able to determine the percentage sodium hydrogen sulphate in toilet cleaner to greater than
1%, which is probably better than the manufacturers' tolerance.
Part of the fun will come from working out the errors :-D
[Edited on 23-9-2008 by ScienceSquirrel]