Question

calculate pH of the buffer solution prepared by mixing 10 mL of 1.5 M HCl with 100 mL of 0.1 M K2CO3 solution. For H2CO3: Ka1= 4.46 e^-7, Ka2= 4.69e^-11

Answer 1

pH = pKa + log(B/A)
mols K2CO3 = M x L.
mols HCl = M x L.
Calculate mols K2CO3 initially.
Calculate mols HCl initially.
I think you will find that one H ion has been added to the CO3^=, and you are half way between CO3^= and H2CO3 meaning that CO3^= and H2CO3 are the same.
Therefore, log B/A = log 1 = 0 and pH = pKa1.
Post any work if you have questions.