Lily P.

asked • 11/02/20

Protolysis of sulfuric acid

Hi!


I have the following question: 0.05 moles of sulfuric acid was mixed with water to the volume of 1 cubic decimetres. What is the pH-value of the solution?


My answer: First I wrote the reaction: H2SO4 + H2O -> HSO4- + H3O+


So reaction shows that 0.05 moles of sulfuric acid gives 0.05 moles of H3O+.

The concentration of it is 0.05/1 = 0.05 M

I recalculate it to pH by -lg0.05 = 1.3


Answer= 1.3


But my compendium answers differently. They say that 1 mole of H2SO4 gives 2 moles of HSO4-

But the further reaction of HSO4- is not complete, because HSO4- is a weak acid: HSO4- + H20 <-> SO42- + H3O+. Surely this reaction would work, but not all 0.05 moles of HSO4- from the first reaction should react here since we have a weak acid and I don't know how the book thinks that both reaction one and two reacts competely and gives us a total of 0.1 moles of H3O+


Thankful for help!

1 Expert Answer

By:

Lily P.

Thank you sir for your help :) Glad to know I wasn't misunderstanding a basic principle.
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11/02/20

Lily P.

I got the final pH to 1.17? I would appreciate it if you can tell me if I am correct or not? :) A million thanks!!
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11/02/20

J.R. S.

tutor
Sorry took so long to get back. Didn't see your comment until just now. I got a final pH of 1.16 so close enough. Maybe rounding differences. Glad I could help.
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11/03/20

Lily P.

Its ok! Thanks anyway for your amazing help
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11/07/20

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