Chapter U6.7, Problem 8E

Interpretation Introduction

Interpretation: The equilibrium constant for the dissociation of methyl violet needs to be explained.

Concept Introduction: The color change for an indicator occurs when the ${\text{H}}^{\text{+}}$ ion concentration is equal to K. This happens when the concentration of HIn molecules is equal to the concentration of the ${\text{In}}^{-}$ ions.

Answer to Problem 8E

Equilibrium constant for the dissociation of methyl violet is ${10}^{-1}$ .

Explanation of Solution

Color changes for an indicator is occurs if ${\text{H}}^{\text{+}}$ ion concentration is equal to constant K.

pH is the negative logarithm of ${\text{H}}^{\text{+}}$ ion concentration. Given, pH is 1. Therefore,

  $\begin{array}{c}\text{pH}=1\\ -\log \left[{\text{H}}^{\text{+}}\right]=1\\ \left[{\text{H}}^{\text{+}}\right]={10}^{-1}\end{array}$

Since, $\left[{\text{H}}^{\text{+}}\right]=\text{K}$

Therefore, K value is ${10}^{-1}$ .

Conclusion

Equilibrium constant for the dissociation of methyl violet is ${10}^{-1}$ .