1. The problem statement, all variables and given/known data What was the concentration of acid S before the titration? 2. Relevant equations MaVa=MbVb 3. The attempt at a solution So for this problem, the solution manual suggests that we use the formula above to solve for the pH of acid S before the titration. But why do we use the concentration of the base before we even add it? Wouldn't it be easier to locate the pH on the graph (which is approximately 3.8) and take 10^-3.8 = 1.6 x 10^-4? The correct answer is B. Thanks in advance.