Q: A 0.10 M solution of barium sulfate ($$\mathrm{BaSO_4}) is $$prepared. The solubility product constant ($$K_{sp}) $$for $$\mathrm{BaSO_4} is$$ $$1.1 \times 10^{-10}. $$What is the molar solubility of $$\mathrm{BaSO_4} in $$pure water?

$$\mathrm{1.0 \times 10^{-5}\ M}$$

Question 1

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

Accepted Answer

A weak acid and its conjugate base

Question 2

A buffer solution is prepared by mixing acetic acid ($$\mathrm{CH_3COOH}) $$and sodium acetate ($$\mathrm{CH_3COONa}). $$Which of the following best explains how this buffer resists changes in pH when a small amount of hydrochloric acid ($$\mathrm{HCl}) is $$added?

Accepted Answer

The acetate ions react with the added $$\mathrm{HCl} to $$form more acetic acid, minimizing the pH change.

Question 3

Which equation is most appropriate for calculating the pH of a buffer solution containing a weak acid and its conjugate base?

Accepted Answer

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

Question 4

A buffer is made by mixing 0.20 mol of ammonia ($$\mathrm{NH_3}) $$and 0.20 mol of ammonium chloride ($$\mathrm{NH_4Cl}) in $$enough water to make 1.0 L of solution. The $$K_b$$ for ammonia is $$1.8 	imes 10^{-5}. $$What is the pH of the buffer? ($$K_w = 1.0 	imes 10^{-14})$$

Accepted Answer

$$\mathrm{pH = 9.25}$$

Question 5

Which of the following statements about buffer capacity is correct?

Accepted Answer

Buffer capacity is greatest when the concentrations of the weak acid and its conjugate base are equal and high.

Question 6

A buffer solution is prepared with $$[HA] = 0.10\ \mathrm{M}$$ and $$[A^-] = 0.10\ \mathrm{M}. If $$the $$pK_a of HA is 5.00$$, what is the pH of the buffer after adding enough strong base to convert 25% of HA to A$$^-$$?

Accepted Answer

$$\mathrm{pH = 5.18}$$

Question 7

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

Accepted Answer

The pH equals the pK$$_a of $$the weak acid.

Question 8

Which of the following best describes the shape of the titration curve for a strong acid-strong base titration?

Accepted Answer

The pH rises gradually and then sharply near the equivalence point, with the equivalence point at pH 7.

Question 9

A 0.10 M solution of barium sulfate ($$\mathrm{BaSO_4}) is $$prepared. The solubility product constant ($$K_{sp}) $$for $$\mathrm{BaSO_4} is$$ $$1.1 	imes 10^{-10}. $$What is the molar solubility of $$\mathrm{BaSO_4} in $$pure water?

Accepted Answer

$$\mathrm{1.0 	imes 10^{-5}\ M}$$

Question 10

How does the presence of a common ion affect the solubility of an ionic compound?

Accepted Answer

It decreases the solubility due to the common ion effect.

Question 11

Which of the following best explains why the solubility of $$\mathrm{CaF_2}$$ increases in acidic solution?

Accepted Answer

Acid reacts with $$\mathrm{F^-}$$ ions, reducing their concentration and shifting the equilibrium to dissolve more $$\mathrm{CaF_2}.$$

Question 12

A solution contains $$\mathrm{Ag^+}$$ and $$\mathrm{Pb^{2+}}$$ ions. You wish to selectively precipitate $$\mathrm{AgCl}$$ ($$K_{sp} = 1.8 	imes 10^{-10}) $$before $$\mathrm{PbCl_2}$$ ($$K_{sp} = 1.7 	imes 10^{-5}). $$What is the minimum concentration of $$\mathrm{Cl^-}$$ required to begin precipitating $$\mathrm{AgCl}$$?

Accepted Answer

$$\mathrm{[Cl^-] = \frac{K_{sp}}{[Ag^+]}}$$

Question 13

Which of the following statements is true regarding the use of ICE tables in buffer calculations?

Accepted Answer

ICE tables help track changes in concentrations of weak acids and their conjugate bases during equilibrium.

Question 14

A solution contains 0.10 M $$\mathrm{Mg^{2+}}$$ and 0.10 M $$\mathrm{Ca^{2+}}. $$You add $$\mathrm{OH^-} to $$selectively precipitate $$\mathrm{Mg(OH)_2}$$ ($$K_{sp} = 1.8 	imes 10^{-11}) $$before $$\mathrm{Ca(OH)_2}$$ ($$K_{sp} = 5.5 	imes 10^{-6}). $$What is the minimum $$\mathrm{[OH^-]}$$ required to start precipitating $$\mathrm{Mg(OH)_2}$$?

Accepted Answer

$$\mathrm{[OH^-] = \sqrt{\frac{K_{sp}}{[Mg^{2+}]}}}$$

Question 15

Which of the following best describes the effect of complex ion formation on the solubility of a sparingly soluble salt?

Accepted Answer

Complex ion formation increases the solubility by removing ions from the equilibrium.

Question 16

During the titration of a polyprotic acid, which of the following is true about the titration curve?

Accepted Answer

There are multiple equivalence points, each corresponding to the loss of a proton.

Question 17

A buffer solution is prepared with $$[HA] = 0.30\ \mathrm{M}$$ and $$[A^-] = 0.10\ \mathrm{M}. If $$the $$pK_a of HA is 4.80$$, what is the pH of the buffer?

Accepted Answer

Question 18

Which of the following is the correct relationship between the reaction quotient ($$Q) $$and the solubility product constant ($$K_{sp}) $$for predicting precipitation?

Accepted Answer

If $$Q \u003e K_{sp}$$, precipitation will occur.

Acid-Base Equilibria, Buffers, Titrations, and Solubility Equilibria

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