1. The problem statement, all variables and given/known data A buffer is made by dissolving 13.0g of sodium dihydrogen phosphate, NaH2PO4, and 15.0g of disodium hydrogen phosphate, Na2HPO4, in a litre of solution. What is the pH of the buffer? a) 7.84 b)7.47 c)7.20 d)6.85 e)6.63 2. Relevant equations pH = -log [H+] 3. The attempt at a solution First, I'm not sure if this is right, but I assumed that NaH2PO4 dissassociates into Na+ and then H2PO4-, and then H+, H+, PO4 3- ions. Second I assumed that it dissassociates into Na+, Na+, H+ and PO4 3- ions. 2) M(Na2HPO4) = 141.96 m=15.0g n=.105664 3) M(NaH2PO4) = 119.98 m=13.0g n=.10835 * 2 = 0.2167 (since hydrogen ion concentration doubles) 4) 0.105664+0.2167=0.322 mol H+ 5) pH = -log(.322) = 0.492 This is completely off. Please help. I realize I have a completely wrong approach, but I don't know what else can be done for this problem.