General Chemistry Answers

HA is a weak acid. Which equilibrium corresponds to the equilibrium constant K_b for A^-?

1. HA (aq) + H₂O (l) ↔ H₂A⁺ (aq) + OH^- (aq)
2. A^- (aq) + H₃O⁺ (aq) ↔ HA (aq) + H₂O (l)
3. HA (aq) + OH^- (aq) ↔ H₂O (l) + H⁺ (aq)
4. A^- (aq) + H₂O (l) ↔ HA (aq) + OH^- (aq)
5. A^- (aq) + OH^- (aq) ↔ HOA^2- (aq)

The pH of a 0.01M solution of a weak base is 10.65. What is the value of K_b for this base?

1)2.0 x 10^-5

2)5.0 x 10^-4

3)5.0 x 10^-20

4)0.073

The pH of a 0.55M solution of hypobromous acid, HOBr, is 4.48. Calculate the value of K_a.

1)3.0 x 10⁴

2)2.0 x 10^-9

3)6.0 x 10^-5

4)3.3 x 10^-5

5)1.1 x 10^-9

Calculate the pH of a buffer solution prepared by dissolving 0.20 mole of cyanic acid (HCNO) and 0.80 mole of sodium cyanate (NaCNO) in enough water to make 1.0 litre of solution.

K_a(HCNO) = 2.0 x 10^-4

1)0.97

2)4.30

3)3.10

4)4.40

5)3.70

What is the pH of a 0.65M sodium carbonate solution? (K_b = 1.8 x 10^-4)

1)10.2

2)12

3)3.9

4)2.0

What is the pH of a 1.3M butyric acid solution? (K_a = 1.54 x 10^-5)

1)4.7

2)5.0

3)2.3

4)2.5

In the reaction

HSO₃^- + HClO₂ ↔ H₂SO₃ + ClO₂^-

The Bronsted bases are:

1)HSO₃^- + HClO₂

2)HSO₃^- + ClO₂^-

3)H₂SO₃ + ClO₂^-

4)HClO₂ + H₂SO₃

An indicator is weak acid (or base) having a conjugate base (or acid) with a significantly different colour. For the titration of a weak base, how would you choose an appropriate indicator?

1)Choose an indicator that has a pK_b close to pK_b of the base

2)Choose an indicator which changes colour anywhere in the pH range 0-7

3)Choose an indicator that has a pK_a close to pK_b of the base

4)Choose an indicator with a pK_b close to the pH of the titration at equivalence

5)Choose an indicator with a pK_a close to the pH of the titration at equivalence

An acid HA has K_a = 2.28 x 10 ^-4. The % ionisation of this acid in a 0.170 M solution of the acid in water is closest to

1. 2.930 %
2. 3.662 %
3. 2.564 %
4. 0.498 %
5. 0.436 %
6. 0.623 %

A 0.100 M solution of a weak acid, HX, has a pH of 2.610. What is the value of K_a for HX?

1)6.03 x 10 ^-6

2)6.03 x 10 ^-4

3)2.45 x 10 ^-2

4)2.45 x 10 ^-1

5)6.03 x 10 ^-5

6)2.45 x 10 ^-3