Why would the pH of a solution not be 7 at the equivalence point of an acid-base titration?
The equivalence point is defined as when you have an equal amount of acid and base. It you have a strong acid and a strong base, the pH at the equivalence point should be pretty close to 7, but if you have a weak acid or a weak base involved, there is not reason why the equivalence point should be at pH 7. You would have a conjugate base or acid that is reasonably basic or acidic at the equivalence point.