Answer
$H_{2}C_{6}H_{7}O_{5}$$^{-} (aq)$ $+$ $H_{2}O$$(l)$ $HC_{6}H_{7}O_{5}$$^{2-} (aq)$ $+$ $H_{3}O$$^{+}(aq)$
Work Step by Step
For $H_{2}C_{6}H_{7}O_{5}$$^{-}$ to act as an acid, it must increase H+ concentration. It can do that by donating a proton and becoming $HC_{6}H_{7}O_{5}$$^{2-}$. This will cause water and a hydrogen ion to form $H_{3}O$$^{+}$. Writing this as a chemical reaction will get you the balanced chemical equation.
