Question

(a) a 0.2 m potassium hydroxide solution is titrated with a 0.1 m nitric acid solution. (i) balanced equation: (ii)what would be observed if the solution was titrated well past the equivalence point using bromthymolblue as the indicator? (bromthymol blue is yellow in acidic solution and blue in basic solution.)

Answer 1

$\text{KOH} (aq) + \text{HNO}_3 (aq) \to \text{KNO}_3 (aq) + \text{H}_2\text{O} (l)$

The solution shall contain only $\text{KNO}_3 (aq)$ (and water) at the equivalence point. Both potassium hydroxide and nitric acid exist as strong electrolytes. As a result,  $\text{KNO}_3 (aq)$, the salt derived from a reaction between the two species would undergo hydrolysis of a negligible extent. This neutralization reaction therefore be neutral at the equilibrium point.

The question states that the solution is "titrated with a ... nitric acid solution" indicating that $\text{HNO}_3$ is added to the initially-basic solution. PH value of the solution would keep decreasing as the volume of the acid added increases. The final solution would be acidic as it contains not only water and $\text{KNO}_3 (aq)$, but some $\text{HNO}_3$ as well. Bromothymol blue would therefore demonstrates a yellow color, the color it present in an acidic solution, at the end of the titration.