Chapter 18, Problem 89A

When methyl red is added to an aqueous solution, a pink color results. When methyl orange is added to the same solution, a yellow color is produced. What is the approximate $\text{pH}$ range of the solution? Use Figure 18.24

Interpretation Introduction

Interpretation:

The $pH$ range of solution is to be found out which becomes pink when methyl red is added and yellow when methyl orange is added.

Concept introduction:

Acid-base indicator is a chemical which changes its color on neutralization.

There are various acid-base indicators like phenolphthalein, methyl orange, bromocresol green, bromocresol purple, phenol red

All have a specific $pH$ value on which solution changes its color that is called as equivalence point.

Answer to Problem 89A

$pH$ range of solution is $4.2-5.6$

Explanation of Solution

The diagram below shows that methyl orange changes its color from pink to yellow close to $pH=4.2$ and methyl red changes its color to pink at $pH<5.6$. Thus, $pH$ range of solution is $4.2-5.6$

Conclusion

Thus, the given solution has $pH$ range $4.2-5.6$.