Q: Which of the following is the correct expression for the ion-product constant for water ($K_w$) at 25°C?

$K_w = [\mathrm{H}^+][\mathrm{OH}^-] = 1 \times 10^{-14}$

Question 1

Which of the following best describes the auto-ionization of water as shown in the first image?

Accepted Answer

Water molecules react with each other to form hydronium and hydroxide ions.

Question 2

Given the equation $\mathrm{pH} = -\log[\mathrm{H}^+]$, what is the pH of a solution with $[\mathrm{H}^+] = 1 	imes 10^{-4}\ \mathrm{M}$?

Accepted Answer

$\mathrm{pH} = 4$

Question 3

Which of the following household substances is most likely to have a pH greater than 10, based on the pH scale image?

Accepted Answer

Bleach

Question 4

If the concentration of $[\mathrm{OH}^-]$ in a solution is $1 	imes 10^{-3}\ \mathrm{M}$, what is the pOH of the solution?

Accepted Answer

$\mathrm{pOH} = 3$

Question 5

Which of the following statements about acids and bases is correct according to the Brønsted-Lowry definition?

Accepted Answer

An acid is a proton donor and a base is a proton acceptor.

Question 6

A solution has a pH of 2. Which of the following best describes this solution?

Accepted Answer

It is strongly acidic.

Question 7

If the pH of a solution is 9, what is the $[\mathrm{H}^+]$ concentration?

Accepted Answer

$1 	imes 10^{-9}\ \mathrm{M}$

Question 8

Which of the following best explains why the pH scale is logarithmic?

Accepted Answer

It allows us to express a wide range of $[\mathrm{H}^+]$ concentrations in a compact form.

Question 9

A sample of pure water at 25°C has $[\mathrm{H}^+] = 1 	imes 10^{-7}\ \mathrm{M}$. What is its pH?

Accepted Answer

$7$

Question 10

If a solution has a pH of 12, which of the following statements is true?

Accepted Answer

The solution is basic and has a low $[\mathrm{H}^+]$ concentration.

Question 11

Which of the following equations correctly relates pH and pOH in aqueous solutions at 25°C?

Accepted Answer

$\mathrm{pH} + \mathrm{pOH} = 14$

Question 12

A solution has $[\mathrm{OH}^-] = 1 	imes 10^{-6}\ \mathrm{M}$. What is the pH of the solution at 25°C?

Accepted Answer

$8$

Question 13

Which of the following best describes the role of water in the auto-ionization reaction shown in the first image?

Accepted Answer

Water acts as both an acid and a base.

Question 14

If you mix equal volumes of a solution with pH 3 and a solution with pH 11, what will be the approximate pH of the resulting mixture?

Accepted Answer

The resulting pH will be closer to 3, because acids dominate in neutralization reactions.

Question 15

Which of the following is a real-world consequence of the auto-ionization of water?

Accepted Answer

It allows water to conduct electricity, even when pure.

Question 16

A laboratory technician accidentally adds enough acid to a solution to change its $[\mathrm{H}^+]$ from $1 	imes 10^{-7}\ \mathrm{M}$ to $1 	imes 10^{-3}\ \mathrm{M}$. By how many units did the pH change?

Accepted Answer

The pH decreased by 4 units.

Question 17

Which of the following best explains why lemon juice is more acidic than milk, as shown in the pH scale image?

Accepted Answer

Lemon juice has a higher $[\mathrm{H}^+]$ concentration than milk.

Question 18

Which of the following is the correct expression for the ion-product constant for water ($K_w$) at 25°C?

Accepted Answer

$K_w = [\mathrm{H}^+][\mathrm{OH}^-] = 1 	imes 10^{-14}$

Acids, Bases, and the pH Scale: Quantitative Aspects of Aqueous Solutions

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