Q: Which of the following best describes the pH of a solution of $\mathrm{NH_4NO_3}$ dissolved in water?

Acidic, because $\mathrm{NH_4^+}$ is the conjugate acid of a weak base.

Q: Which of the following statements about polyprotic acids is correct?

Each successive proton is lost less easily, so $K_{a1} > K_{a2} > K_{a3}$.

Question 1

Which of the following statements best explains why acid strength increases as you move down a group in the periodic table for binary acids (e.g., HF, HCl, HBr, HI)?

Accepted Answer

The bond strength between hydrogen and the central atom decreases, making it easier for the proton to dissociate.

Question 2

Given the following reaction: $\mathrm{CH_3CO_2H(aq) + H_2O(l) ightleftharpoons H_3O^+(aq) + CH_3CO_2^-(aq)}$, and $K_a = 1.8 	imes 10^{-5}$, what is the pH of a $0.10\ \mathrm{M}$ acetic acid solution?

Accepted Answer

$2.87$

Question 3

Which of the following pairs of acids is correctly ordered from weaker to stronger acid?

Accepted Answer

$\mathrm{H_2S < H_2Se}$

Question 4

A $0.25\ \mathrm{M}$ solution of hydrazine ($\mathrm{N_2H_4}$) has $K_b = 1.7 	imes 10^{-6}$. What is the pH of this solution?

Accepted Answer

$11.23$

Question 5

Which of the following best describes the pH of a solution of $\mathrm{NH_4NO_3}$ dissolved in water?

Accepted Answer

Acidic, because $\mathrm{NH_4^+}$ is the conjugate acid of a weak base.

Question 6

A $0.020\ \mathrm{M}$ solution of KF is prepared. Given $K_b$ for $\mathrm{F^-}$ is $1.4 	imes 10^{-11}$, what is the pH of the solution?

Accepted Answer

$11.23$

Question 7

Which of the following statements about polyprotic acids is correct?

Accepted Answer

Each successive proton is lost less easily, so $K_{a1} > K_{a2} > K_{a3}$.

Question 8

Estimate the pH of a $0.10\ \mathrm{M}$ $\mathrm{H_2SO_4}$ solution, given $K_{a2} = 0.012$ for the second deprotonation.

Accepted Answer

$0.96$

Question 9

Which of the following best explains why $\mathrm{HClO_4}$ is a stronger acid than $\mathrm{HClO_3}$?

Accepted Answer

It has more oxygen atoms, increasing the oxidation number of the central atom and stabilizing the conjugate base.

Question 10

A solution of $0.15\ \mathrm{M}$ $\mathrm{HC_2O_4^-}$ is prepared. Given $K_a = 5.25 	imes 10^{-5}$ and $K_b = 1.90 	imes 10^{-10}$, is the solution acidic or basic?

Accepted Answer

Acidic, because $K_a > K_b$ for $\mathrm{HC_2O_4^-}$.

Question 11

Which of the following ions will make an aqueous solution acidic?

Accepted Answer

$\mathrm{Fe^{3+}}$

Question 12

Which of the following best describes the pH of a $0.15\ \mathrm{M}$ $\mathrm{NH_4Cl}$ solution? ($K_b$ for $\mathrm{NH_3}$ is $1.8 	imes 10^{-5}$)

Accepted Answer

$5.04$

Question 13

Which of the following is the correct method to estimate the pH of a solution of a salt of a weak polyprotic acid?

Accepted Answer

Take the average of the relevant $pK_a$ values of the parent acid.

Question 14

Estimate the pH of a solution of monosodium citrate ($\mathrm{NaHC_6H_5O_7}$), given $pK_{a1} = 3.13$, $pK_{a2} = 4.76$, $pK_{a3} = 6.39$ for citric acid.

Accepted Answer

$4.03$

Question 15

In a $0.01\ \mathrm{M}$ solution of 1,4-butanedicarboxylic acid ($K_{a1} = 2.9 	imes 10^{-5}$, $K_{a2} = 5.3 	imes 10^{-6}$), which species is present in the highest concentration?

Accepted Answer

$\mathrm{HO_2CCH_2CH_2CO_2^-}$ (aq)

Question 16

Which of the following best explains why $\mathrm{HClO}$ is a weaker acid than $\mathrm{HClO_4}$?

Accepted Answer

It has fewer oxygen atoms, so the conjugate base is less stabilized by resonance.

Acid-Base Equilibria and Polyprotic Acids: Study Notes for General Chemistry

Study Guide - Practice Questions

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