Question 1

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

Accepted Answer

Water molecules transfer protons to each other, forming hydronium and hydroxide ions.

Question 2

Given the auto-ionization reaction $$2H_2O \rightarrow H_3O^+ + OH^-$$, what is the expression for the equilibrium constant $$K_w$$?

Accepted Answer

$$K_w = [H_3O^+][OH^-]$$

Question 3

At 25°C, the value of $$K_w is$$ $$1.0 	imes 10$$^{-14}$$. If the concentration of $$[H_3O^+]$$ in a solution is 3.7$$ 	imes $$10^{-4} M$$, what is the $$[OH^-]$$ concentration?

Accepted Answer

$$2.7 	imes 10$$^{-11}$$ M

Question 4

A solution at 25°C has $$[OH^-] = 7.42 	imes 10$$^{-11}$$ M. What is the pOH of the solution?

Accepted Answer

$$pOH = 10.13$$

Question 5

If the pH of pure water at 25°C is 7.00, what is the $$[H_3O^+]$$ concentration?

Accepted Answer

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

Question 6

A solution at 25°C has a pH of 1.34. What is the $$[H_3O^+]$$ concentration?

Accepted Answer

$$4.6 	imes 10$$^{-2}$$ M

Question 7

Which of the following statements is true about the relationship between pH and pOH at 25°C?

Accepted Answer

$$pH + pOH = 14$$

Question 8

If a solution at 25°C has $$[H_3O^+] = 1.0 	imes 10$$^{-9}$$ M, is the solution acidic, basic, or neutral?

Accepted Answer

Basic

Question 9

A chemistry student prepares a solution at 25°C with $$[OH^-] = 1.0 	imes 10$$^{-6}$$ M. What is the pH of the solution?

Accepted Answer

$$pH = 8.00$$

Question 10

Which of the following best explains why the $$K_w$$ value changes with temperature?

Accepted Answer

Because the auto-ionization of water is an endothermic process, and increasing temperature increases ionization.

Question 11

A solution at 25°C has $$[H_3O^+] = 1.0 	imes 10$$^{-3}$$ M. Calculate the pOH.

Accepted Answer

$$pOH = 11$$

Question 12

If the $$K_w at 40$$°C is $$2.92 	imes 10$$^{-14}$$, what is the $$[OH^-]$$ in pure water at this temperature?

Accepted Answer

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

Question 13

A solution at 25°C has a pOH of 2.00. What is the $$[OH^-]$$ concentration?

Accepted Answer

$$1.0 	imes 10$$^{-2}$$ M

Question 14

If a solution at 25°C has $$[OH^-] = 1.0 	imes 10$$^{-8}$$ M, what is the $$[H_3O^+]$$ concentration?

Accepted Answer

$$1.0 	imes 10$$^{-6}$$ M

Question 15

A solution at 25°C has a pH of 12. What is the $$[OH^-]$$ concentration?

Accepted Answer

$$1.0 	imes 10$$^{-2}$$ M

Question 16

Which of the following is true for a neutral solution at 25°C?

Accepted Answer

$$[H_3O^+] = [OH^-]$$

Question 17

A solution at 25°C has $$[H_3O^+] = 1.0 	imes 10$$^{-5}$$ M. Is the solution acidic, basic, or neutral?

Accepted Answer

Acidic

Question 18

If the pOH of a solution is 8.00 at 25°C, what is the pH?

Accepted Answer

$$pH = 6.00$$

Question 19

A solution at 25°C has $$[OH^-] = 1.0 	imes 10$$^{-3}$$ M. What is the pOH and is the solution acidic, basic, or neutral?

Accepted Answer

$$pOH = 3$$, basic

Auto-Ionization of Water and pH Calculations

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