Question 1

A weak acid, HA, dissociates in water according to the equation $\mathrm{HA} + \mathrm{H_2O} \rightleftharpoons \mathrm{H_3O^+} + \mathrm{A^-}$. Which of the following is the correct equilibrium constant expression for this dissociation?

Accepted Answer

$K_a = \dfrac{[\mathrm{H_3O^+}][\mathrm{A^-}]}{[\mathrm{HA}]}$

Question 2

Which of the following pairs is a correct example of a conjugate acid-base pair?

Accepted Answer

$\mathrm{H_2O}$ / $\mathrm{OH^-}$

Question 3

A student mixes $0.10$ M acetic acid ($K_a = 1.8 	imes 10^{-5}$) with water. What is the pH of the solution? (Assume $x \ll 0.10$)

Accepted Answer

pH $\approx 3.38$

Question 4

Which of the following reactions represents a Bronsted-Lowry acid-base reaction?

Accepted Answer

$\mathrm{NH_3} + \mathrm{H_2O} \rightarrow \mathrm{NH_4^+} + \mathrm{OH^-}$

Question 5

Given the $K_a$ values for two acids, which statement is correct?

Accepted Answer

The acid with the higher $K_a$ is the stronger acid.

Question 6

A buffer solution is prepared by mixing $0.20$ mol of acetic acid and $0.10$ mol of sodium acetate in $1.0$ L of water. What is the pH of the buffer? ($K_a = 1.8 	imes 10^{-5}$)

Accepted Answer

pH $= 4.74 + \log \left( \dfrac{0.10}{0.20} \right)$

Question 7

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

Accepted Answer

pH $\approx 8.72$

Question 8

Which indicator would be most suitable for marking the endpoint of a titration between a weak acid and a strong base?

Accepted Answer

Phenolphthalein (pH range 8.2–10.0)

Question 9

Given the formula $\mathrm{CaF_2}$, what is the correct expression for its solubility product constant ($K_{sp}$)?

Accepted Answer

$K_{sp} = [\mathrm{Ca^{2+}}][\mathrm{F^-}]^2$

Question 10

A saturated solution of $\mathrm{Ag_2CO_3}$ has a $K_{sp}$ of $8.1 	imes 10^{-12}$. What is the concentration of $\mathrm{Ag^+}$ ions in the solution?

Accepted Answer

$[\mathrm{Ag^+}] = 2x$, where $K_{sp} = 4x^3$

Question 11

Which salt will have the lowest solubility in water if their $K_{sp}$ values are as follows: $\mathrm{BaSO_4}$ ($1.1 	imes 10^{-10}$), $\mathrm{AgCl}$ ($1.8 	imes 10^{-10}$), $\mathrm{PbI_2}$ ($7.1 	imes 10^{-9}$), $\mathrm{CaF_2}$ ($3.2 	imes 10^{-11}$)?

Accepted Answer

$\mathrm{BaSO_4}$

Question 12

If $Q$ for a salt solution is greater than $K_{sp}$, what will happen?

Accepted Answer

A precipitate will form until $Q = K_{sp}$.

Question 13

Which of the following best distinguishes the Bronsted-Lowry acid-base definition from the Lewis acid-base definition?

Accepted Answer

Bronsted-Lowry acids donate protons, while Lewis acids accept electron pairs.

Question 14

A solution contains $0.050$ M $\mathrm{Mg^{2+}}$ and $0.020$ M $\mathrm{Ca^{2+}}$. If $K_{sp}$ for $\mathrm{Mg(OH)_2}$ is $1.8 	imes 10^{-11}$ and for $\mathrm{Ca(OH)_2}$ is $5.5 	imes 10^{-6}$, which hydroxide will precipitate first upon addition of $\mathrm{OH^-}$?

Accepted Answer

$\mathrm{Mg(OH)_2}$

Question 15

Which of the following is the correct net ionic equation for the reaction between $\mathrm{NaOH}$ and $\mathrm{HCl}$ during a titration?

Accepted Answer

$\mathrm{OH^-} + \mathrm{H^+} \rightarrow \mathrm{H_2O}$

Question 16

A buffer is made by mixing $0.25$ mol of ammonia ($\mathrm{NH_3}$) and $0.15$ mol of ammonium chloride ($\mathrm{NH_4Cl}$) in $1.0$ L of water. What is the pH of the buffer? ($K_b = 1.8 	imes 10^{-5}$)

Accepted Answer

pH $= 14 - [4.74 + \log(0.25/0.15)]$

Question 17

Which of the following statements about selective precipitation is correct?

Accepted Answer

Selective precipitation separates ions based on their different $K_{sp}$ values.

Question 18

A solution is prepared by mixing $0.10$ M $\mathrm{Ba^{2+}}$ and $0.10$ M $\mathrm{SO_4^{2-}}$. If $K_{sp}$ for $\mathrm{BaSO_4}$ is $1.1 	imes 10^{-10}$, will a precipitate form?

Accepted Answer

Yes, because $Q > K_{sp}$.

General Chemistry Study Guide: Acids, Bases, Buffers, and Solubility

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