Q: Which equation is used to calculate the pH of a buffer solution when the concentrations of the acid and its conjugate base are known?

$$\mathrm{pH} = pK_a + \log \frac{[\text{base}]}{[\text{acid}]}$$

Question 1

Which of the following best describes a buffer solution?

Accepted Answer

A solution that resists changes in pH when small amounts of H$$^+ or OH$^-$$ are added.

Question 2

A buffer is prepared by mixing 0.100 mol of acetic acid (HC$$_2H$_3O$_2) $$and 0.100 mol of sodium acetate (NaC$$_2H$_3O$_2) in 1.0 L of $$water. If the $$K_a$$ for acetic acid is $$1.8 	imes 10$$^{-5}$$, what is the pH of the buffer?

Accepted Answer

$$\mathrm{pH} = 4.74$$

Question 3

Which equation is used to calculate the pH of a buffer solution when the concentrations of the acid and its conjugate base are known?

Accepted Answer

$$\mathrm{pH} = pK_a + \log \frac{[	ext{base}]}{[	ext{acid}]}$$

Question 4

A buffer solution is made by mixing 0.50 M NH$$_3$$ and 0.20 M NH$$_4Cl. If $$the $$pK_b of NH$_3 is 4.75$$, what is the pH of the solution? (Assume $$pK_a + pK_b = 14)$$

Accepted Answer

$$\mathrm{pH} = 9.55$$

Question 5

Which of the following statements about buffer capacity is correct?

Accepted Answer

Buffer capacity increases with increasing absolute concentrations of both acid and base.

Question 6

A 50.0 mL sample of 0.200 M NaOH is titrated with 0.200 M HNO$$_3. $$What is the pH after adding 30.0 mL of HNO$$_3$$?

Accepted Answer

$$\mathrm{pH} = 12.7$$

Question 7

During the titration of a weak acid with a strong base, why is the pH at the equivalence point greater than 7?

Accepted Answer

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

Question 8

Which indicator would be most appropriate for detecting the equivalence point in the titration of a strong acid with a strong base?

Accepted Answer

Bromothymol blue (pH range 6.0–7.6)

Question 9

Which of the following best explains why the solubility of CaF$$_2$$ decreases in a solution containing NaF?

Accepted Answer

The common ion effect reduces the solubility by increasing the concentration of F$$^-.$$

Question 10

Given the following $$K_{sp}$$ values: AgI ($$1.5 	imes 10$$^{-16}$$), AgBr (7.7$$ 	imes $$10^{-13}$$), AgCl ($$1.6 	imes 10$$^{-10}$$), which salt is the most soluble in water?

Accepted Answer

AgCl

Question 11

A solution contains 0.0150 M Pb(NO$$_3$$)$$_2$$ and 0.00350 M NaBr. Will PbBr$$_2$$ precipitate? ($$K_{sp}$$ for PbBr$$_2$$ = $$4.67 	imes 10$$^{-6}$$)

Accepted Answer

No, because $$Q \u003c K_{sp}.$$

Question 12

Which of the following is true about the relationship between $$K_a$$ and $$K_b$$ for a conjugate acid-base pair?

Accepted Answer

$$K_a 	imes K_b = K_w$$

Question 13

Which of the following compounds will be more soluble in acidic solution than in neutral solution?

Accepted Answer

BaF$$_2$$

Question 14

A solution is 0.085 M in Pb$$^{2+}$$ and 0.025 M in Ag$$^+. If $$selective precipitation is to be achieved using NaCl, which ion will precipitate first?

Accepted Answer

Ag$$^+$$

Question 15

Which of the following best describes an amphoteric hydroxide?

Accepted Answer

A hydroxide that is soluble in both acidic and basic solutions.

Question 16

Which of the following is the correct expression for the solubility product constant ($$K_{sp}) $$for Bi$$_2S$_3$$?

Accepted Answer

$$K_{sp} = [Bi$$^{3+}$$]^2[S$$^{2-}$$]^3$$

Question 17

Which of the following best explains why a supersaturated solution will precipitate when a seed crystal is added?

Accepted Answer

The seed crystal provides a surface for excess solute to crystallize.

Question 18

Which of the following is a correct statement about complex ion formation?

Accepted Answer

Complex ion formation can increase the solubility of a sparingly soluble salt.

Aqueous Ionic Equilibrium: Buffers, Titrations, and Solubility

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