If 1,2,3 4 moles of H3PO4,NaH2PO4,Na2HPO4 and Na3PO4 respectively are mixed together to form an aqueous solution Resulting pH - Chemistry - Equilibrium

Question

If 1,2,3&4 moles of H3PO4,NaH2PO4,Na2HPO4 and Na3PO4
respectively are mixed together to form an aqueous solution
Resulting pH of the solution is If Ka1=10^-3 Ka2=10^-7 Ka3=10^-13

Geetha · Accepted Answer

The conjucate acid base pairs areH3PO4/NaH2PO4  :  Ka1 = 10-3   :  pKa1 = 3NaH2PO4/Na2HPO4  :  Ka2 = 10-7 :  pKa2 = 7Na2HPO4/Na3PO4 : Ka3 = 10-13 :  pKa3 = 13According to Henderson equationpH= pKa + log [salt][Acid]For H3PO4/NaH2PO4 pH= 3 + log [2][1] = 3 +0
3010 = 3
3010For NaH2PO4/Na2HPO4 pH= 7+ log [3][2] = 7 + 0
1761 = 7
1761For Na2HPO4/Na3PO4 pH= 13+ log [4][3] =13 + 0
1249 = 13 1249So the resulting pH= 3
3010 +  7 1761 +13 1249 3 = 7 87

If 1,2,3&4 moles of H3PO4,NaH2PO4,Na2HPO4 and Na3PO4 respectively are mixed together to form an aqueous solution. Resulting pH of the solution is If Ka1=10^-3 Ka2=10^-7 Ka3=10^-13