Question 1

A solution is prepared by dissolving a weak acid, HA, in water. If the acid dissociation constant $$K_a$$ for HA is $$1.8 	imes 10$$^{-5}$$ and the initial concentration of HA is 0.10$ M, what is the pH of the solution? (Assume no initial dissociation and neglect activity coefficients.)

Accepted Answer

$$pH = 4.74$$

Question 2

Which of the following statements best describes the effect of adding NaOH to a buffer solution containing acetic acid and sodium acetate?

Accepted Answer

The buffer will resist changes in pH, but the pH will increase slightly.

Question 3

A student is asked to prepare a buffer with a pH of 7.4 using the Henderson-Hasselbalch equation. Which of the following combinations would be most appropriate?

Accepted Answer

A weak acid with $$pK_a = 7.4$$ and its conjugate base

Question 4

During a titration of a weak acid with a strong base, which region of the titration curve corresponds to the buffer region?

Accepted Answer

Between the initial addition of base and just before the equivalence point

Question 5

Which equation is used to calculate the pH of a buffer solution?

Accepted Answer

$$pH = pK_a + \log \left( \frac{[A^-]}{[HA]} \right)$$

Question 6

A solution contains $$0.10 M $$ammonia ($$NH_3) $$and $$0.10 M $$ammonium chloride ($$NH_4Cl). $$What will happen to the pH if a small amount of HCl is added?

Accepted Answer

The pH will decrease slightly due to the buffer action.

Question 7

Which of the following is true about the equivalence point in a titration of a strong acid with a strong base?

Accepted Answer

The pH at the equivalence point is always 7.

Question 8

Which of the following best describes the common ion effect?

Accepted Answer

The solubility of a salt decreases when a common ion is added.

Question 9

A saturated solution of $$AgCl is $$prepared. If $$K_{sp}$$ for $$AgCl is$$ $$1.8 	imes 10$$^{-10}$$, what is the molar solubility of $$AgCl$$ in pure water?

Accepted Answer

$$1.3 	imes 10$$^{-5}$$ M

Question 10

Which of the following will increase the buffer capacity of a solution?

Accepted Answer

Increasing the concentration of both the weak acid and its conjugate base

Question 11

If $$Q_{sp}$$ for a solution is greater than $$K_{sp}$$, what will happen?

Accepted Answer

Precipitation will occur until $$Q_{sp}$$ equals $$K_{sp}.$$

Question 12

Which of the following is the correct expression for the acid dissociation constant $$K_a$$ for a weak acid $$HA$$?

Accepted Answer

$$K_a = \frac{[H^+][A^-]}{[HA]}$$

Question 13

A buffer is made by mixing $$0.50$$ mol of acetic acid ($$CH_3COOH) $$and $$0.50$$ mol of sodium acetate ($$CH_3COONa) in$$ $$1.0 L of $$water. If $$pK_a of $$acetic acid is $$4.76$$, what is the pH of the buffer?

Accepted Answer

$$pH = 4.76$$

Question 14

Which of the following is true about polyprotic acids?

Accepted Answer

Each successive proton is harder to remove than the previous one.

Question 15

Which of the following is the correct relationship between $$pK_a$$ and acid strength?

Accepted Answer

A lower $$pK_a$$ indicates a stronger acid.

Question 16

During a titration of a weak base with a strong acid, what is the pH at the equivalence point?

Accepted Answer

Less than 7

Question 17

Which of the following is the correct formula for calculating $$pOH$$?

Accepted Answer

$$pOH = -\log[OH^-]$$

Question 18

A buffer solution is prepared using $$0.20$$ mol of $$NH_3$$ and $$0.10$$ mol of $$NH_4Cl in$$ $$1.0 L of $$water. If $$pK_b$$ for $$NH_3 is$$ $$4.75$$, what is the pOH of the buffer?

Accepted Answer

$$pOH = 4.45$$

Question 19

Which of the following best explains why buffer solutions are important in biological systems?

Accepted Answer

They maintain a constant pH, which is crucial for enzyme activity.

Acid-Base Chemistry, Buffers, Titrations, and Solubility Equilibria: Study Notes

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