Question

What is the \(\rm pH\) after 0.150 \({\rm mol}\) of \(\rm HCl\) is added to the buffer from Part A? Assume no volume change on the addition of the acid.

The \(\rm pH\) from Part A = 6.05.

Answer 1

I need the concentrations of the reactants of buffer added to know that. I don't need the value of pH.

However let me help you. Usually when you add acid to an acidic buffer like this, you are actually increasing the concentration of that acid, and pH should be slower so, using hendersson hasselbach equation:

pH = pKa + log (S/A)

all you have to do is put the value of pKa given, and the concentration of salt and acid would be:

pH = pKA + log (S-HCl/A´+HCl)

Just put the values of S and A obtained in part a) substract in one and sum in the other and calculate the new pH. You should get a lower value of pH.

Hope this helps