Q: At 25°C, the value of $$K_w is$$ $$1.0 \times 10$$^{-14}$$. What is the concentration of $$[\mathrm{H}^+]$$ in pure water at this temperature?

$$1.0 \times 10$$^{-7}$$\ \mathrm{M}$$

Q: Given $$K_w = 2.93 \times 10$$^{-14}$$ at 50°C, what is the concentration of $$[\mathrm{H}^+]$$ in pure water at this temperature?

$$1.71 \times 10$$^{-7}$$\ \mathrm{M}$$

Q: A solution at 50°C has $$[\mathrm{H}^+] = 1.71 \times 10$$^{-7}$$\ \mathrm{M}. $$What is the $$[\mathrm{OH}^-] in $$this solution?

$$1.71 \times 10$$^{-7}$$\ \mathrm{M}$$

Q: If the $$[\mathrm{OH}^-] in a $$solution at 25°C is $$1.0 \times 10$$^{-5}$$\ \mathrm{M}$$, what is the $$[\mathrm{H}^+]$$?

$$1.0 \times 10$$^{-9}$$\ \mathrm{M}$$

Q: A neutral solution at 0°C has a $$K_w of$$ $$1.14 \times 10$$^{-15}$$. What is the $$[\mathrm{H}^+]$$ in this solution?

$$1.07 \times 10$$^{-8}$$\ \mathrm{M}$$

Question 1

Which of the following best describes the process of water self-ionization?

Accepted Answer

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

Question 2

What is the correct equilibrium expression for the ionization of water?

Accepted Answer

$$K_w = [\mathrm{H}^+][\mathrm{OH}^-]$$

Question 3

At 25°C, the value of $$K_w is$$ $$1.0 	imes 10$$^{-14}$$. What is the concentration of $$[\mathrm{H}^+]$$ in pure water at this temperature?

Accepted Answer

$$1.0 	imes 10$$^{-7}$$\ \mathrm{M}$$

Question 4

If the temperature increases from 25°C to 50°C, what happens to the value of $$K_w$$ for water?

Accepted Answer

$$K_w$$ increases

Question 5

Given $$K_w = 2.93 	imes 10$$^{-14}$$ at 50°C, what is the concentration of $$[\mathrm{H}^+]$$ in pure water at this temperature?

Accepted Answer

$$1.71 	imes 10$$^{-7}$$\ \mathrm{M}$$

Question 6

Which statement best explains why $$K_w$$ increases with temperature?

Accepted Answer

The self-ionization of water is endothermic, so increasing temperature shifts the equilibrium to produce more ions.

Question 7

A solution at 50°C has $$[\mathrm{H}^+] = 1.71 	imes 10$$^{-7}$$\ \mathrm{M}. $$What is the $$[\mathrm{OH}^-] in $$this solution?

Accepted Answer

$$1.71 	imes 10$$^{-7}$$\ \mathrm{M}$$

Question 8

Which of the following best describes an amphoteric substance?

Accepted Answer

A substance that can act as both an acid and a base

Question 9

If the $$[\mathrm{OH}^-] in a $$solution at 25°C is $$1.0 	imes 10$$^{-5}$$\ \mathrm{M}$$, what is the $$[\mathrm{H}^+]$$?

Accepted Answer

$$1.0 	imes 10$$^{-9}$$\ \mathrm{M}$$

Question 10

A neutral solution at 0°C has a $$K_w of$$ $$1.14 	imes 10$$^{-15}$$. What is the $$[\mathrm{H}^+]$$ in this solution?

Accepted Answer

$$1.07 	imes 10$$^{-8}$$\ \mathrm{M}$$

Question 11

Which of the following equations correctly represents the self-ionization of water?

Accepted Answer

$$2\ \mathrm{H}_2\mathrm{O}(l) \rightleftharpoons \mathrm{H}_3\mathrm{O}^+(aq) + \mathrm{OH}^-(aq)$$

Question 12

If a solution at 100°C has $$K_w = 5.13 	imes 10$$^{-13}$$, what is the $$[\mathrm{H}^+]$$ in pure water at this temperature?

Accepted Answer

$$7.16 	imes 10$$^{-7}$$\ \mathrm{M}$$

Question 13

Which of the following statements is true about the relationship between $$[\mathrm{H}^+]$$ and $$[\mathrm{OH}^-] in $$pure water at any temperature?

Accepted Answer

$$[\mathrm{H}^+] = [\mathrm{OH}^-]$$

Question 14

A sample of water at 50°C is found to have $$[\mathrm{H}^+] = 1.0 	imes 10$$^{-6}$$\ \mathrm{M}. Is $$the solution acidic, basic, or neutral?

Accepted Answer

Acidic, because $$[\mathrm{H}^+] \u003e [\mathrm{OH}^-]$$

Question 15

Which of the following best explains why the pH of pure water decreases as temperature increases?

Accepted Answer

The concentration of $$[\mathrm{H}^+]$$ increases as $$K_w$$ increases with temperature.

Question 16

A nurse prepares a saline solution and wants to ensure it is neutral at 25°C. What should the $$[\mathrm{H}^+]$$ and $$[\mathrm{OH}^-]$$ concentrations be?

Accepted Answer

$$[\mathrm{H}^+] = [\mathrm{OH}^-] = 1.0 	imes 10$$^{-7}$$\ \mathrm{M}$$

Self-Ionization of Water and the Ion Product Constant ($K_w$)

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