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A LevelChemistryOCRExam Questions5. Physical Chemistry & Transition ElementsAcids, Bases & Buffers

Acids, Bases & Buffers (OCR A Level Chemistry A): Exam Questions

Exam code: H432

4 hours34 questions

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Acids, Bases & Buffers

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1
Sme Calculator1 mark

The pH of hydrochloric acid, HCl (aq), with a concentration of 0.15 mol dm-3 is

  • 0.15

  • 0.82

  • -0.82

  • 1.00

Choose your answer

2
Sme Calculator1 mark

What is the pH of a 0.008 mol dm-3 solution of sodium hydroxide, NaOH, at 25 °C?

(Kw = 1.00 x 10-14 mol2 dm-6 at 25 °C)

  • 2.10

  • 11.90

  • 12.90

  • 10.90

Choose your answer

31 mark

The pH curve represents which type of titration? 

5-3-q3

  • Strong alkali being added to weak acid

  • Strong acid being added to weak alkali

  • Weak acid being added to strong alkali

  • Weak acid being added to weak alkali

Choose your answer

41 mark

Which statement about buffers is correct?

  • A buffer resists small changes in pH

  • A buffer can be formed from sodium hydroxide and an excess of ethanoic acid

  • Buffers are able to resist changes in pH when strong acids and alkalis are added

  • If a strong acid is added to a buffer solution the concentration of the weak acid decreases

Choose your answer

51 mark

The correct expression for the acid dissociation constant, Ka, for the dissociation of benzoic acid, C6H5COOH is

  • K subscript a space equals space fraction numerator open square brackets straight C subscript 6 straight H subscript 5 COOH close square brackets over denominator open square brackets straight H subscript blank superscript plus close square brackets open square brackets straight C subscript 6 straight H subscript 5 COO subscript blank superscript minus close square brackets end fraction

  • K subscript a space equals space fraction numerator open square brackets straight H subscript blank superscript plus close square brackets open square brackets straight C subscript 6 straight H subscript 5 COO subscript blank superscript minus close square brackets over denominator open square brackets straight C subscript 6 straight H subscript 5 COOH close square brackets end fraction

  • K subscript a space equals space open square brackets straight H subscript blank superscript plus close square brackets open square brackets straight C subscript 6 straight H subscript 5 COO subscript blank superscript minus close square brackets

  • K subscript a space equals space open square brackets straight C subscript 6 straight H subscript 5 COOH close square brackets

Choose your answer

11 mark

Which of the following statements is correct? 

  • As temperature increases, the pH value of pure water decreases

  • As temperature decreases, the pH value of pure water decreases

  • The pH of water is unaffected by temperature

  • Pure water is not neutral

Choose your answer

21 mark

Which of the following is the pH of 0.08 mol dm-3 Ba(OH)2? 

(Kw = 1.00 x 10-14 mol2 dm-6 at 25 ℃)

  • 14.80

  • 13

  • 13.20

  • 12.90

Choose your answer

31 mark

What is the pH of ethanoic acid with a concentration of 0.75 mol dm-3 at 25 oC? 

(Ka of ethanoic acid at 25 ℃ = 1.78 x 10-5 mol dm-3)

  • 4.62

  • 0.12

  • 9.72

  • 2.44

Choose your answer

41 mark

The pH range of four different indicators are:

Indicator

pH range for colour change

Methyl orange

3.2 - 4.4 

Phenolphthalein

8.2 - 10.0

Thymol blue

1.2 - 2.8 

Bromothymol blue 

6.0 - 7.6 

Which indicator would be suitable for a titration involving hydrochloric acid and ammonia?

  • Methyl orange

  • Phenolphthalein

  • Thymol blue

  • Bromothymol blue

Choose your answer

51 mark

What is the pH of a buffer solution containing 0.0413 moles of ethanoic acid and 0.0398 moles of sodium ethanoate in 500 cm3 at 25 oC? 

(Ka of ethanoic acid at 25 ℃ = 1.78 x 10-5 mol dm-3)

  • 1.08

  • 4.73

  • 2.91

  • 4.77

Choose your answer

61 mark

Which statement is correct for the following equation?

NH4+ + OH– ⇌ H2O + NH3

  • NH4+ is the base

  • H2O is the conjugate acid

  • NH3 is the conjugate acid

  • OH– is the acid

Choose your answer

71 mark

25.00 cm3 of 0.25 mol dm−3 nitric acid is added to 12.50 cm3 of 0.10 mol dm−3 sodium hydroxide.

What is the pH of the resulting mixture?

  • 0.88

  • 0.60 

  • 2.30

  • 13.00

Choose your answer

1
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A buffer solution is prepared by mixing 200 cm3 of 2.00 mol dm–3 propanoic acid, CH3CH2COOH, with 600 cm3 of 1.00 mol dm–3 sodium propanoate, CH3CH2COONa.

Ka for CH3CH2COOH = 1.32 × 10–5 mol dm–3

What is the pH of the buffer solution?

  • 4.58

  • 4.70

  • 5.06

  • 4.88

Choose your answer

21 mark

Which of the following statements is/are correct?

  1. The initial concentration of H2CO3 can be used to calculate Ka.

  2. When calculating the Ka of H2CO3, [H+] equals [A-] at equilibrium.

  3. The value of Ka is independent of temperature. 

  • 1, 2 and 3

  • Only 1 and 2

  • Only 2 and 3

  • Only 1

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31 mark

X g of potassium ethanoate was added to ethanoic acid to form a buffer solution with a final volume of 250 cm3 and a pH of 4.70. The final concentration of ethanoic acid was 0.40 mol dm-3. Ka for ethanoic acid is 1.8 x 10-5 mol dm-3.

What was the mass of potassium ethanoate added?

  • 68.0 g

  • 5.41 g

  • 41.6 g

  • 8.85 g

Choose your answer

41 mark

A student has 0.72 mol dm-3 of potassium hydroxide solution, a solution of sodium hydroxide with a pH of 13.4 and a solution of hydrogen cyanide with a pH of 4.20 and a Ka of 6.2 x 10-10 mol dm-3.

Kw = 1.00 x 10-14 mol2 dm-6.

What is the pH of potassium hydroxide, the concentration of sodium hydroxide (mol dm-3) and the concentration of hydrogen cyanide (mol dm-3) respectively?

  • 13.90, 0.60, 6.42

  • 13.80, 0.25, 4.05

  • 13.90, 0.25, 6.42

  • 14.70, 0.60, 4.05

Choose your answer

51 mark

What is the pH of a buffer solution formed when 2.5 g of NaOH is added to 1.0 dm3 of 0.15 mol dm-3 solution of ethanoic acid? Ka for ethanoic acid is 1.74 x 10-5 mol dm-3.

  • 4.61

  • 4.19

  • 5.96

  • 5.58

Choose your answer