Question

A solution contains thymol blue indicator. for each of the following, indicate if the solution is acidic, basic or neutral and the color of the solution. [H^+] > [OH^-] [H^+] < [OH^-] [H^+] = [OH^-]

Answer 1

Thymol Blue gives following colours at the different pH

Thymol blue (pH indicator )                                     

                            below pH 1.2                    above pH 2.8                    below pH 8.0                        above pH 9.6

Colour             Brownish Red     $\rightleftharpoons$               Yellow                                  Yellow                                 Blue

a) $\r\left [ H^{+} \right ]\, >\, \left [ OH^{-} \right ]$ $\left [ H^{+} \right ]\, >\, \left [ OH^{-} \right ]$              means the solution is acidic, so colour of the solution will be red/brownish red

b) $\left [ H^{+} \right ]\, < \, \left [ OH^{-} \right ]$                means the solution is basic, so the colour of solution will be blue

c) $\left [ H^{+} \right ]\, = \, \left [ OH^{-} \right ]$                means the solution is at neutral pH, (pH = 7). so the solution will give yellow colour

                                                      (pH 2.8 to 8.0 colour shown is yellow)