Q: A buffer solution is most effective when:

The ratio $$\frac{[\text{base}]}{[\text{acid}]} is $$close to 1.

Question 1

Which of the following mixtures will create a buffer solution?

Accepted Answer

A solution of 0.50 M CH3COOH and 0.50 M CH3COONa

Question 2

A buffer solution is prepared by mixing 0.10 mol of acetic acid (CH3COOH) and 0.10 mol of sodium acetate (CH3COONa) in enough water to make 1.0 L of solution. If the $$pK_a of $$acetic acid is 4.74, what is the pH of the buffer?

Accepted Answer

$$pH = 4.74$$

Question 3

Which of the following best explains why blood pH remains relatively constant even when small amounts of acid or base are introduced?

Accepted Answer

Blood contains buffer systems such as $$H_2CO_3/$$HCO_3$$^-$$ that resist pH changes.

Question 4

Calculate the pH of a buffer solution containing 0.20 M NH3 and 0.10 M NH4Cl. ($$K_b$$ for NH3 = $$1.8 	imes 10$$^{-5}$$, pK_w = 14.00$)

Accepted Answer

$$pH = 9.43$$

Question 5

Which of the following acids would be the best choice to combine with its sodium salt to make a buffer solution with $$pH = 4.25$$?

Accepted Answer

Formic acid ($$pK_a = 3.74)$$

Question 6

A buffer solution is most effective when:

Accepted Answer

The ratio $$\frac{[	ext{base}]}{[	ext{acid}]} is $$close to 1.

Question 7

What is the pH at the equivalence point when 50.0 mL of 0.10 M CH3COOH is titrated with 0.10 M NaOH? ($$K_a = 1.8 	imes 10$$^{-5}$$)

Accepted Answer

$$pH = 8.72$$

Question 8

Which indicator would be most appropriate for a titration with an equivalence point at $$pH = 9.0$$?

Accepted Answer

Phenolphthalein ($$pK_a \approx 9.3)$$

Question 9

A solution contains 0.10 M Ba(NO3)2, 0.10 M Na2SO4, and 0.10 M NaNO3. In which solution is BaSO4 most soluble?

Accepted Answer

0.10 M NaNO3

Question 10

The solubility product constant ($$K_{sp}) $$for AgBr is $$7.7 	imes 10$$^{-13}$$. What is the solubility of AgBr in pure water?

Accepted Answer

$$8.8 	imes 10$$^{-7}$$ M

Question 11

Which of the following will increase the solubility of CuS in water?

Accepted Answer

Adding NaCN

Question 12

A solution is prepared by mixing 25 mL of 1 M NaOH with 50 mL of 1 M NH3. What type of solution is formed?

Accepted Answer

A buffer solution

Question 13

Which of the following statements about the common ion effect is correct?

Accepted Answer

The presence of a common ion decreases the solubility of an ionic compound.

Question 14

For the dissolution of $$CaF_2(s$$) \rightleftharpoons $$Ca^{2+}(aq) + 2F^-(aq$$)$$, what is the K$$_{sp}$$ expression?

Accepted Answer

$$K_{sp} = [Ca$$^{2+}$$][F^-]^2$$

Question 15

Which cation will precipitate first when potassium sulfate is added to a solution containing equal concentrations of $$Ba^{2+}$$, $$Pb^{2+}$$, and $$Ca^{2+}$$? ($$K_{sp}$$ values: $$BaSO_4 = 1.07$$ 	imes $$10^{-10}$$, $$PbSO_4 = 1.82$$ 	imes $$10^{-8}$$, $$CaSO_4 = 7.10$$ 	imes $$10^{-5})$$

Accepted Answer

$$Ba^{2+}$$

Question 16

Which of the following best describes the effect of lowering the pH on the solubility of $$Mg(OH)_2$$?

Accepted Answer

Solubility increases

Question 17

What is the $$K_f$$ expression for the formation of $$Ag(NH_3$)_2^+$$ from $$Ag^+$$ and $$NH_3$$?

Accepted Answer

$$K_f = \frac{[Ag(NH_3$)_2^+]}{[Ag^+][NH_3$]^2}$$

Question 18

A buffer contains equal amounts of a weak acid and its conjugate base and has a pH of 5.25. Which would be a reasonable value of buffer pH after the addition of a small amount of acid?

Accepted Answer

5.15

Question 19

Which of the following best describes an amphoteric hydroxide?

Accepted Answer

It is more soluble in both acidic and basic solutions.

Aqueous Ionic Equilibrium: Buffers, Titration Curves, and Solubility Equilibria

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