Chapter U6.123, Problem 6E

Interpretation Introduction

Interpretation: Bromocresol green is turn blue when dissolved in a base needs to be explained.

Concept Introduction: Le Chatelier’s principles, also known as the equilibrium law, are used to predict the effect of some changes on a system in chemical equilibrium. According to him equilibrium adjusts the forward and backward reactions in such a way to accept the changes affecting the equilibrium conditions.

Answer to Problem 6E

Since, equilibrium in basic solution favored the formation of product ions ${\text{H}}^{\text{+}}$ and ${\text{In}}^{-}$ . So, the colour of bromocresol green turns blue.

Explanation of Solution

In bromocresol green colour of HIn is yellow and ${\text{In}}^{-}$ is blue.

  $\text{HIn}\left(\text{aq}\right)\rightleftharpoons {\text{H}}^{\text{+}}\left(\text{aq}\right)+{\text{In}}^{-}\left(\text{aq}\right)$

If a base is added to a solution with an indicator, then concentration of ${\text{H}}^{\text{+}}$ decreases. The system responds by making more product ions ${\text{H}}^{\text{+}}$ and ${\text{In}}^{-}$ . Therefore, the colour of the bromocresol green is become blue.

Conclusion

After adding base on bromocresol equilibrium shifts towards the product. So, the colour is blue.