DATBootcamp Bio question on diprotic

[cc609]

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The question on DATbootcamp is

What is H+ concentration in .0006M in H2C2O4.

Kq for H2C2O4 is 6e-12

Since H2C2O4 is diprotic , I multiplied .0006M by 2 and did the Square Root of Ka and Molarity.

The answer was wrong and I saw that they did not multiply by 2 and just used .0006. Why do we not do the normality thing for this?

 

[FeralisExtremum]

This isn't a neutralization, so you're not reacting with a strong base until every single proton comes off of it. This is standard dissolving of an acid in aqueous solution. Since it's a weak acid, not every proton is going to dissociate before you hit the equilibrium. In this question, we're just looking for the extent to which the one proton that will dissociate, does.

Even with a diprotic strong acid (H2SO4) you still don't use normality because again, only the first proton completely dissociates, and the second only partially.

This differs from say, Ba(OH)2 where you have to count OH twice because it does in fact completely dissociate into two parts in solution.