Q: A buffer is most effective when:

The ratio $$\left( \frac{[\text{base}]}{[\text{acid}]} \right) is $$close to 1 and both concentrations are large.

Question 1

Which of the following best explains why blood is able to maintain a nearly constant pH, even when small amounts of acid or base are introduced?

Accepted Answer

Blood contains a buffer system composed of $$\mathrm{H_2CO_3}$$ and $$\mathrm{$$HCO_3$$^-}$$ that resists changes in pH.

Question 2

A buffer solution is prepared by mixing 0.50 M $$\mathrm{NH_3$}$$ and 0.20 M $$\mathrm{NH_4Cl}. If $$the $$pK_b of$$ $$\mathrm{NH_3$} is 4.75$$, what is the pH of the buffer? ($$pK_a + pK_b = 14)$$

Accepted Answer

$$\mathrm{pH} = 9.25$$

Question 3

Which of the following actions will destroy a buffer solution composed of 0.050 M $$\mathrm{HC_2H_3O_2}$$ and 0.250 M $$\mathrm{NaC_2H_3O_2} in 1.0 L$$?

Accepted Answer

Adding 0.050 moles of $$\mathrm{NaOH}$$

Question 4

A buffer is most effective when:

Accepted Answer

The ratio $$\left( \frac{[	ext{base}]}{[	ext{acid}]} ight) is $$close to 1 and both concentrations are large.

Question 5

What is the pH of a buffer that is 0.14 M HF ($$pK_a = 3.15) $$and 0.071 M KF?

Accepted Answer

2.39

Question 6

Which acid would be the best choice to combine with its conjugate base to make a buffer with pH = 4.55?

Accepted Answer

HB; $$pK_a = 4.25$$

Question 7

A 1.0 L buffer solution is composed of 0.10 M HA and 0.10 M A$$^-. $$Calculate the pH upon adding 0.022 moles of HCl to the solution. ($$pK_a = 4.25)$$

Accepted Answer

4.06

Question 8

Which of the following statements about buffer capacity is correct?

Accepted Answer

A concentrated buffer can neutralize more added acid or base than a dilute buffer.

Question 9

Which of the following best describes the effect of adding NaCl to a saturated solution of PbCl$$_2$$?

Accepted Answer

The solubility of PbCl$$_2$$ decreases due to the common ion effect.

Question 10

Calculate the molar solubility of AgCl in pure water at 25$$^\circC$$. ($$K_{sp} = 1.77 	imes 10$$^{-10}$$)

Accepted Answer

$$1.33 	imes 10$$^{-5}$$ M

Question 11

Which of the following will increase the solubility of CaF$$_2 in $$water?

Accepted Answer

Decreasing the pH of the solution

Question 12

A solution contains 0.059 M Mg$$^{2+}. $$What is the minimum [OH$$^-$$] necessary to just begin to precipitate Mg(OH)$$_2$$? ($$K_{sp} = 2.06 	imes 10$$^{-13}$$)

Accepted Answer

$$1.87 	imes 10$$^{-6}$$ M

Question 13

Which of the following statements about titration curves is correct?

Accepted Answer

The equivalence point of a strong acid-strong base titration occurs at pH 7.

Question 14

During the titration of a weak acid with a strong base, the pH at the half-equivalence point is:

Accepted Answer

Equal to the pK$$_a of $$the weak acid

Question 15

Which of the following is true for the titration of 10.0 mL of 0.100 M HCl with 0.100 M NaOH, 10.0 mL of 0.100 M HF with 0.100 M NaOH, 10.0 mL of 0.100 M H$$_2C$_6H$_6O$_6$$ with 0.100 M NaOH, and 10.0 mL of 0.100 M NH$$_3$$ with 0.100 M HCl?

Accepted Answer

All four titrations will require the same volume (of titrant) to reach their first equivalence point.

Question 16

Which of the following best describes the effect of adding NH$$_3 to a $$solution in equilibrium with AgCl(s)? ($$K_{sp}$$ for AgCl = $$1.77 	imes 10$$^{-10}$$, K_f$ for [Ag(NH_3$)_2$]$$^+$$ = 1.7$$ 	imes $$10^7)$$

Accepted Answer

The solubility of AgCl increases due to complex ion formation.

Question 17

Which of the following is the correct expression for the solubility product constant ($$K_{sp}) $$for PbBr$$_2$$?

Accepted Answer

$$K_{sp} = [\mathrm{Pb$$^{2+}$$}][\mathrm{Br^-}]^2$$

Chapter 18: Ionic Equilibrium – Buffers, Titrations, and Solubility

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