Chapter 20, Problem 7STP

Interpretation Introduction

Interpretation:

When the ph value is given then the concentration of hydrogen ion is to be calculated.

Concept introduction:

The $\text{pH}$ value is defined as the negative logarithm of the hydrogen ion concentration in mol/L

Answer to Problem 7STP

Correct answer: B is correct

B. ${\text{3×10}}^{\text{-3}}\text{mol/L}$

Explanation of Solution

Reason for correct option:

The $\text{pH}$ value is defined as the negative logarithm of the hydrogen ion concentration in mol/L.

${\text{pH= -log}}_{\text{10}}\left[{\text{H}}^{\text{+}}\right]$

Where $\left[{\text{H}}^{\text{+}}\right]$ is the concentration of hydrogen ion in mol/L.

The hydrogen ion concentration is can be calculated as

$\begin{array}{l}\left[{\text{H}}^{\text{+}}\right]{\text{=10}}^{\text{-pH}}\\ {\text{=10}}^{\text{-2}\text{.5}}\\ \text{=}\frac{\text{1}}{{\text{10}}^{\text{2}\text{.5}}}\\ \text{=}\frac{\text{1}}{\text{316}\text{.22}}\\ {\text{=3×10}}^{\text{-3}}\text{mol/L}\end{array}$

Conclusion

Reasons for incorrect options:

1. Not matches with calculated value.
2. Not matches with calculated value.
3. Not matches with calculated value.