Q: Which of the following is a correct application of the Henderson-Hasselbalch equation for a buffer made from a weak acid and its conjugate base?

$pH = pK_a + \log \left( \frac{[\text{base}]}{[\text{acid}]} \right)$

Question 1

A solution is prepared by mixing 0.30 mol of acetic acid ($CH_3COOH$) and 0.30 mol of sodium acetate ($CH_3COONa$) in enough water to make 1.0 L of solution. What is the pH of this solution? ($K_a$ for acetic acid = $1.8 	imes 10^{-5}$)

Accepted Answer

$pH = 4.74$

Question 2

Which of the following statements is TRUE regarding the effect of adding a soluble salt containing a common ion to a solution of a weak acid at equilibrium?

Accepted Answer

The pH of the solution increases.

Question 3

A solution contains 0.20 M HF and 0.10 M HCl. What is the concentration of $F^-$ ions in the solution? ($K_a$ for HF = $6.8 	imes 10^{-4}$)

Accepted Answer

$1.4 	imes 10^{-3}$ M

Question 4

Which of the following best explains why the addition of sodium acetate to acetic acid solution decreases the $[H^+]$ concentration?

Accepted Answer

The common ion effect shifts the equilibrium to the left, reducing $[H^+]$.

Question 5

A buffer solution is made by mixing 0.12 M lactic acid ($HC_3H_5O_3$) and 0.10 M sodium lactate ($NaC_3H_5O_3$). What is the pH of the buffer? ($K_a$ for lactic acid = $1.4 	imes 10^{-4}$)

Accepted Answer

$pH = 3.77$

Question 6

Which of the following is a correct application of the Henderson-Hasselbalch equation for a buffer made from a weak acid and its conjugate base?

Accepted Answer

$pH = pK_a + \log \left( \frac{[	ext{base}]}{[	ext{acid}]} ight)$

Question 7

A buffer is prepared by adding 0.300 mol $CH_3COOH$ and 0.300 mol $CH_3COONa$ to enough water to make 1.0 L. If 0.020 mol of NaOH is added to this buffer, what will be the new pH? ($K_a$ for acetic acid = $1.8 	imes 10^{-5}$)

Accepted Answer

$pH = 4.81$

Question 8

During a strong acid-strong base titration, 50.0 mL of 0.100 M HCl is titrated with 0.100 M NaOH. What is the pH at the equivalence point?

Accepted Answer

$pH = 7.00$

Question 9

In the titration of 50.0 mL of 0.100 M acetic acid ($CH_3COOH$) with 0.100 M NaOH, what is the pH at the equivalence point? ($K_a$ for acetic acid = $1.8 	imes 10^{-5}$)

Accepted Answer

$pH = 8.72$

Question 10

Which of the following salts will have its solubility increased in acidic solution?

Accepted Answer

BaF$_2$

Question 11

The solubility product constant ($K_{sp}$) for $CaF_2$ is $3.9 	imes 10^{-11}$ at 25°C. What is the molar solubility of $CaF_2$ in pure water?

Accepted Answer

$2.1 	imes 10^{-4}$ M$

Question 12

Which of the following actions will increase the solubility of $AgBr$ in water?

Accepted Answer

Decreasing the pH

Question 13

A solution contains $1.0 	imes 10^{-4}$ M $Ag^+$ and $2.0 	imes 10^{-4}$ M $Pb^{2+}$. When $Cl^-$ is added, which salt will precipitate first? ($K_{sp}$ for $AgCl = 1.8 	imes 10^{-10}$, $K_{sp}$ for $PbCl_2 = 1.7 	imes 10^{-5}$)

Accepted Answer

$AgCl$

Question 14

Which condition must be met for an ionic compound to precipitate from a solution of its constituent ions?

Accepted Answer

$Q > K_{sp}$

Question 15

A buffer is made by adding $NH_4Cl$ to $NH_3$ solution. If the desired pH is 9.00 and the volume is 2.0 L, how many moles of $NH_4Cl$ are needed? ($K_b$ for $NH_3 = 1.8 	imes 10^{-5}$)

Accepted Answer

0.36 mol

Question 16

Which of the following will NOT affect the value of $K_{sp}$ for $MA_3$ in water at 298 K?

Accepted Answer

Changing the temperature of the solution

Question 17

A solution contains $0.010$ M $Ag^+$ and $0.30$ M $NH_3$. What is the effect of adding $NH_3$ on the concentration of free $Ag^+$ ions?

Accepted Answer

It drastically reduces the concentration of $Ag^+$ ions due to complex ion formation.

Question 18

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

Accepted Answer

The solubility decreases due to the common ion.

Common Ion Effect, Buffers, and pH Calculations

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