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A Level - Concentration Calculation?
I have to calculate the concentration of sulphuric acid, H2SO4. I've already worked out the H+ concentration to be 0.56 but what do I do now? And why?
Thanks for any help
I think I am, incorrectly, assuming that it is fully dissociated. That's how it usually goes.
1 Answer
- pisgahchemistLv 710 years agoFavorite Answer
That's a bit tricky and depends upon your level of chemistry knowledge. If you are familiar with acid/base equilibria and know what Ka is and what an ICE table is, then you are good to go. On the other hand, if are you assuming that H2SO4 is completely dissociated (which is not correct) then it is a bit simpler, but will result in an error.
H2SO4 is a strong acid, but only for the first H that comes off....
H2SO4 --> H+ + HSO4-
The resulting HSO4- ion is a weak acid, and is only partially dissociated.
HSO4- <==> H+ + SO4^2- ..... Ka = 1.2 x 10^-2
The hydrogen ions in a solution of H2SO4 come primarily from the first H+ that is released, but HSO4- also makes some contribution.
If on the other hand you (incorrectly) assume that H2SO4 --> 2H+ + SO4^2- then the concentration of H2SO4 is half of the hydrogen ion concentration.
============== Follow up ==============
You can safely assume that the H2SO4 concentration will be between 0.28M and 0.56M, with neither of the two extremes being correct.