Chapter 4.3, Problem 97PE

Scientists use pH scale to represent the level of acidity or alkalinity of a liquid. This is based on the molar concentration of hydrogen ions, $\left[{\text{H}}^{+}\right]$. Since the values of $\left[{\text{H}}^{+}\right]$ vary over a large range, $1\times {10}^0$ mole per liter to $1\times {10}^{-14}$ mole per liter (mol/L), a logarithmic scale is used to compute pH, The formula $\text{pH}=-\text{log}\left[{\text{H}}^{+}\right]$ represents the pH of a liquid as a function of its concentration of hydrogen ions, $\left[{\text{H}}^{+}\right]$. The pH scale ranges from 0 to 14. Pure water is taken as neutral having a pH of 7. A pH less than 7 is acidic. A pH greater than 7 is alkaline (or basic). For Exercises 97–98, use the formula for pH, Round pH values to 1 decimal place.

Vinegar and lemon juice are both acids. Their $\left[{\text{H}}^{+}\right]\text{ values are }5.2\times {10}^{-3}\text{mol}/\text{L}$ $\text{and }1\times {10}^{-2}\text{mol}/\text{L}$, respectively.

a. Find the pH for vinegar.

b. Find the pH for lemon juice.

c. Which substance is more acidic?