Question 1

Which of the following best describes what happens when a hydrogen ion (H⁺) is formed from a water molecule?

Accepted Answer

A hydrogen atom leaves its electron behind, becoming a single proton with a positive charge.

Question 2

What is the correct chemical equation representing the dissociation of water?

Accepted Answer

$$2H_2O \rightleftharpoons H_3O^+ + OH^-$$

Question 3

In the dissociation of water, what does the molecule that loses a hydrogen ion become?

Accepted Answer

Hydroxide ion ($$OH^-)$$

Question 4

Why is $$H^+$$ often used to represent $$H_3O^+ in $$aqueous solutions?

Accepted Answer

Because $$H^+$$ does not exist on its own and is actually associated with water as $$H_3O^+.$$

Question 5

A water molecule rarely breaks apart. Approximately how often does this occur?

Accepted Answer

Every 55 million molecules

Question 6

What effect does adding certain kinds of solutes have on the balance of water dissociation?

Accepted Answer

It can disrupt the balance between $$H_3O^+$$ and $$OH^-$$ ions.

Question 7

Which of the following statements about the hydronium ion ($$H_3O^+) is $$correct?

Accepted Answer

$$H_3O^+ is $$formed when a water molecule gains a hydrogen ion.

Question 8

If a solution has an increased concentration of $$OH^-$$ ions, what can be inferred about its pH?

Accepted Answer

The pH is basic.

Question 9

Which of the following best explains why $$H^+$$ ions do not exist freely in water?

Accepted Answer

They associate with water molecules to form $$H_3O^+.$$

Question 10

A student adds a salt to pure water and observes a change in the balance of $$H_3O^+$$ and $$OH^-$$ ions. What is the most likely explanation?

Accepted Answer

The salt disrupts the equilibrium, changing the concentrations of $$H_3O^+$$ and $$OH^-.$$

Question 11

Which of the following is a correct description of the relationship between $$H_2O$$, $$H_3O^+$$, and $$OH^- in $$water?

Accepted Answer

$$H_2O$$ molecules can dissociate to form $$H_3O^+$$ and $$OH^-$$ ions.

Question 12

Which of the following would most likely disrupt the equilibrium of water dissociation?

Accepted Answer

Adding a strong acid or base.

Question 13

If the concentration of $$H_3O^+ in a $$solution increases, what happens to the concentration of $$OH^-$$?

Accepted Answer

It decreases.

Question 14

Which of the following is true about the autoionization of water?

Accepted Answer

It is a rare event, occurring in about one out of every 55 million water molecules.

Question 15

A solution is found to have equal concentrations of $$H_3O^+$$ and $$OH^-. $$What can be concluded about this solution?

Accepted Answer

It is neutral.

Water, Hydrogen Ions, and the Chemistry of Life

Study Guide - Practice Questions