Sulaiman
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At what concentration is sulphuric acid hygroscopic ?
If I leave sulphuric acid exposed to the atmosphere
'concentrated' acid will absorb water from the atmosphere and dilute itself,
'dilute' acid will evaporate mostly water into the atmosphere, concentrating itself.
Where is the equilibrium ?
How is it determined ?
[Edited on 3-10-2018 by Sulaiman]
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fusso
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Not only is sulfuric acid hygroscopic in concentrated form but its solutions are hygroscopic down to concentrations of 10% v/v or below.
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Sulaiman
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How is the 10% arrived at ?
what variables are involved ?
temperature, humidity etc.
Edit : off to the shed for a while to add conc. sulphuric acid to saturated copper sulphate solution.
... care to guess what happens ?
... back soon
... slight delay due to water temperature,
heated water, dissolved copper sulphate, now filtering warm solution ...
[Edited on 3-10-2018 by Sulaiman]
[Edited on 3-10-2018 by Sulaiman]
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fusso
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Quote: Originally posted by Sulaiman  | How is the 10% arrived at ?
what variables are involved ?
temperature, humidity etc.
Edit : off to the shed for a while to add conc. sulphuric acid to saturated copper sulphate solution.
... care to guess what happens ?
... back soon
[Edited on 3-10-2018 by Sulaiman] |
I guess CuSO4.5H2O dropping out? And crystal size dependent on addition
rate and solution temperature?
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DavidJR
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You could always do some experiments to determine that- just leave open beakers containing known mass of various concentrations of sulphuric acid, and
weigh them after a few days
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Sulaiman
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sure, but I'd like to know the theoretical background.
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While waiting for my (so far) 10 ml copper sulphate solution, saturated at 25.5oC and 5 ml sulphuric acid to cool down;
The thread on nitration made me wonder how concentrated must sulphuric acid be for nitration,
or to dehydrate sugars as in the carbon foam demonstration,
or to act as a desiccant in a drying box etc.
I recently calculated that there are about 10.6 acid molecules per water molecule in azeotropic sulphuric acid,
and about 3.5 acid molecules per water molecule at 95% w/w acid.
Just random things floating around in my head that need to be filed away.
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O.K. the solution has cooled down and deposited small pentahydrate-coloured crystals.
If I can find solubility data for copper sulphate in dilute sulphuric acid
I'll put this on my 'experiments to be re-visited' list,
doing this accurately may be interesting.
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