Chemistry Test Acids and Bases 5

Question 1

What is the percent dissociation of a weak acid HA if [HA]₀ = 0.1 M and [H⁺] at equilibrium = 0.001 M?

Accepted Answer

1%

Answer

Percent dissociation = ([H⁺]/[HA]₀) × 100 = (0.001/0.1) × 100 = 1%.

Question 2

Which of the following is the conjugate acid of HPO₄²⁻?

Accepted Answer

H₂PO₄⁻

Answer

The conjugate acid of HPO₄²⁻ is formed by adding one proton: H₂PO₄⁻.

Question 3

When a polyprotic acid like H₃PO₄ dissociates, which dissociation step releases the most H⁺ per mole of acid?

Accepted Answer

The first dissociation

Answer

The first dissociation has the largest Ka because removing the first proton from a neutral molecule is energetically most favorable.

Question 4

A student adds a few drops of universal indicator to an unknown solution and observes a green color. The solution is most likely:

Accepted Answer

Neutral

Answer

Universal indicator shows green around pH 7, indicating a neutral solution.

Question 5

Which of the following best explains why a larger Ka value corresponds to a stronger acid?

Accepted Answer

A larger Ka means the equilibrium favors products (H⁺ and A⁻)

Answer

Ka = [H⁺][A⁻]/[HA]; a larger Ka indicates the equilibrium lies toward dissociation products, meaning more H⁺ is produced.

Chemistry Practice Test