Q: Which of the following statements about buffer solutions is TRUE?

A buffer is most effective when $$[\text{base}] = [\text{acid}].$$

Q: Which of the following will NOT result in the precipitation of $$AgCl$$ ($$K_{sp} = 1.8 \times 10$$^{-10}$$) from a solution containing $$[Ag^+] = 1.0 \times $$10^{-5} M$$?

Adding $$Cl^-$$ until $$[Cl^-] = 1.0 \times 10$$^{-5}$$ M

Q: A solution contains 0.10 M $$Ca^{2+}$$ and 0.10 M $$F^-. $$Will $$CaF_2$$ ($$K_{sp} = 3.45 \times 10$$^{-11}$$) precipitate?

Yes, because $$Q = [Ca$$^{2+}$$][F^-]^2 = 0.10 \times (0.10)^2$ = 1.0 \times 10$$^{-3}$$ \u003e K_{sp}$$

Question 1

Which of the following best describes the common-ion effect?

Accepted Answer

The decrease in solubility of an ionic compound when a solution already contains one of the ions present in the compound.

Question 2

A buffer solution is prepared by mixing 0.20 mol of acetic acid ($$CH_3COOH) $$and 0.20 mol of sodium acetate ($$NaCH_3COO) in $$enough water to make 1.0 L of solution. Given $$K_a = 1.8 	imes 10$$^{-5}$$, what is the pH of the buffer? (Use pK_a$$ = -\log K_a$$)

Accepted Answer

$$pH = 4.74$$

Question 3

Which of the following statements about buffer solutions is TRUE?

Accepted Answer

A buffer is most effective when $$[	ext{base}] = [	ext{acid}].$$

Question 4

What is the pH of a solution made by mixing 0.10 mol of $$HCl$$ and 0.10 mol of $$NaOH in $$enough water to make 1.0 L of solution?

Accepted Answer

$$pH = 7.00$$

Question 5

Which of the following will increase the solubility of $$CaF_2$$ ($$K_{sp} = 3.45 	imes 10$$^{-11}$$) in water?

Accepted Answer

Adding $$HCl to $$the solution.

Question 6

A solution is prepared by mixing 0.15 M $$NH_3$$ and 0.10 M $$NH_4Cl. $$Given $$K_b$$ for $$NH_3 is$$ $$1.8 	imes 10$$^{-5}$$, what is the pH of the solution? (Use $$pOH = pK_b + \log\left(\frac{[	ext{acid}]}{[	ext{base}] }ight)$$ and pK_b$$ = -\log K_b$$)

Accepted Answer

$$pH = 9.26$$

Question 7

Which of the following best explains why the pH at the equivalence point of a weak acid-strong base titration is greater than 7?

Accepted Answer

The conjugate base of the weak acid hydrolyzes to produce $$OH^-$$ ions.

Question 8

If $$K_{sp}$$ for $$BaSO_4 is$$ $$1.1 	imes 10$$^{-10}$$, what is the molar solubility of $$BaSO_4$$ in pure water?

Accepted Answer

$$1.05 	imes 10$$^{-5}$$ M

Question 9

Which of the following will NOT result in the precipitation of $$AgCl$$ ($$K_{sp} = 1.8 	imes 10$$^{-10}$$) from a solution containing $$[Ag^+] = 1.0 	imes $$10^{-5} M$$?

Accepted Answer

Adding $$Cl^-$$ until $$[Cl^-] = 1.0 	imes 10$$^{-5}$$ M

Question 10

A buffer is made by mixing 0.50 mol of $$HF$$ and 0.25 mol of $$NaF in 1.0 L of $$solution. Given $$K_a = 6.8 	imes 10$$^{-4}$$, what is the pH of the buffer?

Accepted Answer

$$pH = 2.97$$

Question 11

Which of the following best describes the effect of adding $$NaCH_3COO ($$sodium acetate) to a solution of acetic acid at equilibrium?

Accepted Answer

The equilibrium shifts to the left, decreasing $$[H^+]$$ and increasing pH.

Question 12

Which of the following is TRUE about the solubility of $$CaF_2 in 0.10 M$$ $$NaF$$ compared to pure water?

Accepted Answer

The solubility of $$CaF_2 is $$lower in 0.10 M $$NaF$$ due to the common-ion effect.

Question 13

A solution contains 0.10 M $$Ca^{2+}$$ and 0.10 M $$F^-. $$Will $$CaF_2$$ ($$K_{sp} = 3.45 	imes 10$$^{-11}$$) precipitate?

Accepted Answer

Yes, because $$Q = [Ca$$^{2+}$$][F^-]^2 = 0.10 	imes (0.10)^2$ = 1.0 	imes 10$$^{-3}$$ \u003e K_{sp}$$

Question 14

Which of the following best explains why the pH of a 1.0 M $$HCl$$ solution is not exactly 0?

Accepted Answer

Activity effects and ion pairing cause deviations from ideality at high concentrations.

Question 15

Which of the following is the correct Henderson-Hasselbalch equation for a buffer made from a weak acid ($$HA) $$and its conjugate base ($$A^-$$)?

Accepted Answer

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

Question 16

A 0.10 M solution of $$NH_3$$ ($$K_b = 1.8 	imes 10$$^{-5}$$) is titrated with 0.10 M $$HCl$$. What is the pH at the equivalence point?

Accepted Answer

$$pH \u003c 7$$ because the solution contains $$NH_4$$^+$$, a weak acid.

Question 17

Which of the following factors does NOT affect the solubility of a salt in water?

Accepted Answer

The color of the salt.

Question 18

A solution contains $$0.10 M$$ $$Pb^{2+}$$ and $$0.10 M$$ $$F^-. $$Will $$PbF_2$$ ($$K_{sp} = 4.0 	imes 10$$^{-8}$$) precipitate?

Accepted Answer

Yes, because $$Q = [Pb$$^{2+}$$][F^-]^2 = 0.10 	imes (0.10)^2$ = 1.0 	imes 10$$^{-3}$$ \u003e K_{sp}$$

Chapter 17: Additional Aspects of Aqueous Equilibria (Chem 1220 Study Notes)

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