I wrote that when an acid is present, it will react with the indicator, according to the equation: H^{+}_{(aq)} + Ind^{-}_{(aq)} \rightleftharpoons HInd_{(aq)}, and when a base is present, it will react with the indicator, according to the equation: HInd^{+}_{(aq)} + OH^{-}_{(aq)}...