Question 1

Which of the following best describes the composition of a buffer solution?

Accepted Answer

A weak acid and its conjugate base

Question 2

A buffer is prepared by mixing 0.100 M acetic acid ($$HC_2H_3O_2) $$and 0.100 M sodium acetate ($$NaC_2H_3O_2). $$What will happen to the pH if a small amount of HCl is added?

Accepted Answer

The pH will decrease slightly

Question 3

Which equation is used to calculate the pH of a buffer solution when the 'x is small' approximation is valid?

Accepted Answer

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

Question 4

A buffer solution is made by mixing 0.050 M benzoic acid ($$HC_7H_5O_2) $$and 0.150 M sodium benzoate ($$NaC_7H_5O_2). If$$ $$K_a = 6.5 	imes 10$$^{-5}$$, what is the pH of the buffer?

Accepted Answer

$$pH = 5.37$$

Question 5

Which of the following statements about buffer capacity is correct?

Accepted Answer

Buffer capacity is highest when the concentrations of acid and conjugate base are equal

Question 6

A 1 L buffer solution contains 0.100 mol HA and 0.100 mol A$$^-. If 0.025 $$mol of HCl is added, what are the new amounts of HA and A$$^-$$ after the reaction?

Accepted Answer

HA: 0.125 mol, A$$^-$$: 0.075 mol

Question 7

Which of the following best explains why a buffer resists changes in pH upon addition of a small amount of strong acid?

Accepted Answer

The strong acid is neutralized by the buffer's conjugate base

Question 8

Which of the following buffer systems would be most effective at maintaining a pH of 9.0?

Accepted Answer

A buffer with $$pK_a = 9.0$$

Question 9

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

Accepted Answer

$$[HA] = [A^-]$$ and $$pH = pK_a$$

Question 10

A student adds 0.010 mol of NaOH to two different 1 L buffer solutions, both with a total of 0.20 mol acid and base. Solution I has 0.10 mol HA and 0.10 mol A$$^-$$, while Solution II has 0.18 mol HA and 0.020 mol A$$^-. $$Which solution will experience a greater change in pH?

Accepted Answer

Solution II, because it has less conjugate base to neutralize the added base

Question 11

Which of the following best describes the common ion effect?

Accepted Answer

The addition of a salt containing a common ion decreases the solubility of a weak electrolyte

Question 12

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

Accepted Answer

The pH is always equal to 7

Question 13

A 25.0 mL sample of 0.100 M HCl is titrated with 0.100 M NaOH. What is the pH after 30.0 mL of NaOH has been added?

Accepted Answer

$$pH = 12.22$$

Question 14

Which of the following indicators would be most appropriate for the titration of a strong acid with a strong base?

Accepted Answer

Phenolphthalein (pH range 8.3–10.0)

Question 15

Which of the following statements about solubility product ($$K_{sp}) is $$correct?

Accepted Answer

$$K_{sp} is $$the equilibrium constant for the dissolution of a solid salt into its ions

Question 16

Which of the following will increase the solubility of $$CaF_2 in $$water?

Accepted Answer

Lowering the pH

Question 17

A solution contains 0.0150 M Pb(NO$$_3$$)$$_2$$ and 0.00350 M NaBr. Will a precipitate of PbBr$$_2$$ form? ($$K_{sp}$$ for PbBr$$_2$$ = $$6.6 	imes 10$$^{-6}$$)

Accepted Answer

Yes, because $$Q \u003e K_{sp}$$

Question 18

Which group of cations can be separated from a mixture by adding Cl$$^-$$ ions to form insoluble chlorides?

Accepted Answer

Group 1: Ag$$^+$$, Pb$$^{2+}$$, Hg$$_2$$^{2+}$$

Aqueous Ionic Equilibrium: Buffers, Titrations, and Solubility

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