APCE Acids & Bases

Question 1

What defines an acid according to the Brønsted-Lowry theory?

Accepted Answer

An acid donates a proton.

Answer

According to the Brønsted-Lowry theory, an acid is defined as a proton (H⁺) donor. When an acid reacts, it gives up a hydrogen ion to another substance, which acts as a base. This definition focuses on the transfer of protons in acid-base reactions.

Question 2

What is the pH of a neutral solution?

Accepted Answer

7.

Answer

A neutral solution has a pH of 7 at 25°C. This specific pH value indicates that the concentration of hydrogen ions (H⁺) is equal to the concentration of hydroxide ions (OH⁻) in the solution. Pure water is a classic example of a neutral solution.

Question 3

What is the relationship between pH and hydrogen ion concentration?

Accepted Answer

As the concentration of H⁺ increases, pH decreases.

Answer

pH is defined as the negative logarithm of the hydrogen ion concentration (pH = -log[H⁺]). Therefore, as the concentration of H⁺ ions increases, the pH value decreases, indicating a more acidic solution. Conversely, a lower H⁺ concentration leads to a higher pH.

Question 4

Which of the following is a strong acid?

Accepted Answer

HCl (Hydrochloric acid).

Answer

Hydrochloric acid (HCl) is classified as a strong acid because it completely dissociates into its ions (H⁺ and Cl⁻) when dissolved in water. This complete ionization means that virtually all HCl molecules donate their protons, leading to a high concentration of H⁺ ions in the solution. In contrast, weak acids only partially dissociate.

Question 5

What is the conjugate base of HCl?

Accepted Answer

Cl⁻.

Answer

When an acid donates a proton (H⁺), the remaining species is its conjugate base. For HCl, when it loses a proton, it forms the chloride ion (Cl⁻). Therefore, Cl⁻ is the conjugate base of the strong acid HCl.

AP Practice Test

AP Practice Test

APCE Acids & Bases