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Sulaiman
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[*] posted on 28-3-2017 at 15:58
How to measure sulphuric acid concentration ?


Other than by careful, tedious, wasteful titrations,
how can I easily and quickly determine the concentration (% w/w) of H2SO4 in the range 93% to 98% to the nearest 1%?

Density measurements are not useful as they are very sensitive to errors near azeotropic concentrations,
Electrical conductivity similarly seems useful only from 96% to 100%
Sonic velocity measurement could work, but too complicated.
so
what have I missed ?




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j_sum1
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Mood: inert even with vigorous stirring.

[*] posted on 28-3-2017 at 16:28


How is a titration wasteful?
To get 1% accuracy you need to be able to measure to +/- 1%. Let's double this target for initial weighing -- that means drawing out about 2g (or just over 1mL) of acid and measuring its mass to the nearest 0.01g. Dilute to a reasonable volume using whatever volumetric flask you have. In general, titrations give better accuracy the more dilute they are. If you have a 500mL or 1000mL flask you are probably in the zone. Throw some in your burette and titrate away. Good technique and repetition should get you a result within 0.5% accuracy fairly easily.

Running the errors:
minimum:
0.995(weighing)×0.995(titration)=0.990025
maximum:
1.005×1.005=1.010025

So, result within 1% for the expense of 1mL of acid.

Getting error to below 0.1% will take a bit more effort and expense. But I am pretty happy with 1% for anything I do at home.


(All this assumes that you have something decent to titrate against. NaOH is no good since it absorbs moisture from the air. Probably the easiest standard is to prepare some anhydrous Na2CO3 from bicarbonate. This does introduce weak base issues but should be manageable since H2SO4 is a strong acid.)
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Sulaiman
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[*] posted on 28-3-2017 at 23:04


D'oh .... thanks j_sum1,
I had a mental lapse - I forgot that I can dilute before titration :(
(so no longer wasteful, just tedious ... I can accept that :)




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[*] posted on 28-3-2017 at 23:13


Nobody knows what kind of needle to use to handle highly corrosive substances with a glass syringe?



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clearly_not_atara
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[*] posted on 29-3-2017 at 00:00


It appears from some Googling that nickel alloys such as Hastelloy and Inconel are suited for this purpose, as is 316 (molybdenum) stainless steel. I suspect that copper will tolerate bromine to some extent as well:

http://www.balseal.com/sites/default/files/tr60c_02070713261...

[Edited on 29-3-2017 by clearly_not_atara]
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JJay
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[*] posted on 29-3-2017 at 00:21


Quote: Originally posted by clearly_not_atara  
It appears from some Googling that nickel alloys such as Hastelloy and Inconel are suited for this purpose, as is 316 (molybdenum) stainless steel. I suspect that copper will tolerate bromine to some extent as well:

http://www.balseal.com/sites/default/files/tr60c_02070713261...

[Edited on 29-3-2017 by clearly_not_atara]


That's interesting. This link gives both Hastelloy and 316 steel a D rating for handling bromine, the same rating given to aluminum: http://www.graco.com/content/dam/graco/ipd/literature/misc/c... The substances you mention (with the exception of copper) are mainly intended to handle high temperatures; I'm not sure that they would resist hydrochloric acid well.

I'm not really sure where to get copper needles and doubt they would hold an edge for very long... I was thinking something more like ceramic or perhaps platinum-iridium alloy might work well but have never seen needles made of such exotic materials....






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clearly_not_atara
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[*] posted on 29-3-2017 at 00:54


They are alloy families after all. I guess that Balseal uses grades specially formulated to handle chemicals, whatever that might require. I believe that copper reacts quite slowly with bromine at room temperature. But from the looks of that you might need a specially-designed alloy.

I think I'd bet on a copper needle before glass. Who knows? These are stainless:

https://www.hamiltoncompany.com/~/media/Files/Syringes%20and...
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[*] posted on 29-3-2017 at 07:05



In an all glass syringe what is the plunger made from? glass
Just wondering how is there a good seal for plunger to tube wall.

If you obtain a glass tube and heat in a flame it is very easy to make your own 'needle' by just pulling on the softened tube and extending it out untill you have a very thin neck. It it very easy to do.
They you have to get a plunger for the tube which might not be so simple.

Having looked them up on ebay I guess glass is the answer.
http://www.ebay.com/itm/GLASS-SYRINGE-1cc-LOT-OF-2-LUER-TIP-...

It would be easy to heat a borosilicate syringe (output end) in a hot flame and pull untill you have a thin enough section for you 'needle'. Some of the syringe would then be unusable I guess but should not be a problem.

[Edited on 29-3-2017 by yobbo II]
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