Chapter 3.3, Problem 97PE

Scientists use the $\text{pH}$ scale to represent the level of acidity or alkalinity of a liquid. This is based on the molar concentration of hydrogen ions, $[{\text{H}}^{+}].$ Since the values of $[{\text{H}}^{+}]$ vary over a large range, $1\times {10}^0$ mole per liter to $1\times {10}^{-14}$ mole per liter $\left(\text{mol/L}\right),$ a logarithmic scale is used to compute $\text{pH}\text{.}$ The formula

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

represents the pH of a liquid as a function of its concentration of hydrogen ions, ${\text{[H}}^{\text{+}}\text{]}\text{.}$

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 $\text{pH}\text{.}$ Round $\text{pH}$ values to 1 decimal place.

Vinegar and lemon juice are both acids. Their $[{\text{H}}^{+}]$ values are $5.0\times {10}^{-3} \text{mol/L and }1\times {10}^{-2} \text{mol/L},$ respectively.

a. Find the $\text{pH}$ for vinegar.

b. Find the $\text{pH}$ for lemon juice.

c. Which substance is more acidic?