polyprotic acids

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polyprotic acids

Postby 005391550 » Wed Jan 22, 2020 8:58 am

when calculating the H+ concentration of a polyprotic acid (ex: H2SO4) would you calculate the H+ concentration of each separate reaction and then add it together or would you treat as one system and write the second equation based on the results of the first one?

Jason Wu 1E
Posts: 101
Joined: Thu Jul 25, 2019 12:15 am

Re: polyprotic acids

Postby Jason Wu 1E » Wed Jan 22, 2020 10:05 am

You would need to calculate it twice I believe and then add the concentration of [H+] together. This is because the equilibrium constant is different for the removal of the first proton compared to the second one. Thus Ka1 will be greater than Ka2.

Kevin Xu 4F
Posts: 50
Joined: Fri Aug 09, 2019 12:16 am

Re: polyprotic acids

Postby Kevin Xu 4F » Wed Jan 22, 2020 1:44 pm

You would need to calculate the dissociation separately, first using Ka and then finding the concentration of the second acid and using the Ka2 to find the remaining H+ concentration. You then add the two H+'s together to find pH. Also, for some problems, you don't have to calculate the second dissociation because the Ka2 is so small and it won't change the H+ concentration significantly from the first dissociation step.

Sue Bin Park 2I
Posts: 52
Joined: Mon Jun 17, 2019 7:24 am

Re: polyprotic acids

Postby Sue Bin Park 2I » Wed Jan 22, 2020 6:30 pm

Do you have to account for the amount of H+ already present from the first deprotonation in the Initial row of ur second deprotonation ICE table?

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