Q: A solution has $$[\mathrm{H_3O^+}] = 2.5 \times 10$$^{-3}$$\ \mathrm{M}. $$What is the $$[\mathrm{OH^-}] at 25$^\circC$$?

$$4.0 \times 10$$^{-12}$$\ \mathrm{M}$$

Question 1

Which of the following statements best describes a Brønsted–Lowry acid?

Accepted Answer

A substance that donates a proton (H$$^+) to $$another substance.

Question 2

Given the reaction: $$\mathrm{NH_3$(aq) + H_2O(l) \rightleftharpoons NH_4$^+(aq) + OH^-(aq)}$$, identify the conjugate acid–base pairs.

Accepted Answer

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

Question 3

Which of the following is a limitation of the Arrhenius theory of acids and bases?

Accepted Answer

It cannot explain the behavior of acids in non-aqueous solutions.

Question 4

Which of the following species is a Brønsted–Lowry base?

Accepted Answer

$$\mathrm{NH_3$}$$

Question 5

A solution has $$[\mathrm{H_3O^+}] = 2.5 	imes 10$$^{-3}$$\ \mathrm{M}. $$What is the $$[\mathrm{OH^-}] at 25$^\circC$$?

Accepted Answer

$$4.0 	imes 10$$^{-12}$$\ \mathrm{M}$$

Question 6

Which of the following best explains why HI is a stronger acid than HF?

Accepted Answer

The H–I bond is weaker and easier to break than the H–F bond.

Question 7

What is the pH of a 0.025 M solution of HNO$$_3 (a $$strong acid)?

Accepted Answer

1.60

Question 8

Which of the following salts will produce a basic solution when dissolved in water?

Accepted Answer

NaCN

Question 9

Calculate the pH of a 0.10 M solution of NaCN. ($$K_a$$ for HCN = $$4.9 	imes 10$$^{-10}$$, K_w = 1.0$$ 	imes $$10^{-14})$$

Accepted Answer

11.15

Question 10

Which of the following is a Lewis acid in the reaction $$\mathrm{Cu$$^{2+}$$ + 4NH_3 \rightarrow [Cu(NH_3$)_4]^{2+}}$$?

Accepted Answer

$$\mathrm{Cu$$^{2+}$$}$$

Question 11

Which of the following indicators would be most suitable for detecting the endpoint of a titration between a strong acid and a strong base?

Accepted Answer

Bromothymol blue (pH range 6.0–7.6)

Question 12

Which of the following statements is true regarding 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

A 0.10 M solution of HCN has a pH of 5.15. What is the percent dissociation of HCN in this solution?

Accepted Answer

0.0070%

Question 14

Which of the following factors increases the acid strength of oxoacids H$$_nYO$_m$$?

Accepted Answer

Increasing the number of oxygen atoms bonded to Y

Question 15

Which of the following best describes the effect of adding a strong base to a solution containing a weak acid and its conjugate base?

Accepted Answer

The pH increases slightly due to the buffer effect.

Question 16

Which of the following is the correct expression for the acid dissociation constant ($$K_a) $$for the reaction $$\mathrm{HA(aq) + H_2O(l) \rightleftharpoons H_3O^+(aq) + A^-(aq)}$$?

Accepted Answer

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

Question 17

Which of the following best explains why the second dissociation constant ($$K_{a2}) of a $$polyprotic acid is always smaller than the first ($$K_{a1}$$)?

Accepted Answer

It is harder to remove a proton from a negatively charged species than from a neutral one.

Question 18

A solution is prepared by dissolving 0.25 M NH$$_4Br in $$water. Predict whether the solution will be acidic, basic, or neutral, and explain why.

Accepted Answer

Acidic, because NH$$_4^+ is $$the conjugate acid of a weak base.

Aqueous Equilibria: Acids and Bases – Study Notes

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