A LevelChemistryAQAExam Questions5. Advanced Physical Chemistry (A Level only)5.6 Further Acids & Bases Calculations (A Level only)

Further Acids & Bases Calculations (A Level only) (AQA A Level Chemistry)

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5.6 Further Acids & Bases Calculations (A Level only)

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11 mark

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

  • Ka =  fraction numerator left square bracket straight C subscript 6 straight H subscript 5 COOH right square bracket over denominator left square bracket straight H to the power of plus right square bracket left square bracket straight C subscript 6 straight H subscript 5 COO to the power of minus right square bracket end fraction

  • Ka = fraction numerator left square bracket straight H to the power of plus right square bracket left square bracket straight C subscript 6 straight H subscript 5 COO to the power of minus right square bracket over denominator left square bracket straight C subscript 6 straight H subscript 5 COOH right square bracket end fraction

  • Ka = [H+][C6H5COO-]

  • Ka = [C6H5COOH]

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21 mark

The pH curve represents which type of titration? further-c

  • 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

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31 mark

What is the pH of a buffer solution containing 0.80 mol dm-3 solution of ethanoic acid, CH3COOH, and 0.80 mol dm-3 sodium ethanoate, CH3COONa at 25 ℃?

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

  • 0.10

  • 5.75

  • 3.75

  • 4.75

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41 mark

Which of the following statements about pKa is correct?

  • The higher the value, the stronger the acid

  • The lower the value. the stronger the acid

  • pKa = 10-Ka

  • Ka = -log pKa

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51 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

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11 mark

The pH of ethanoic acid with a concentration of 0.75 mol dm-3 at 25 ℃ is:

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

  • 4.62

  • 0.12

  • 9.72

  • 2.44

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21 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

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31 mark

The pH curve below represents a weak acid, strong base titration 

5-6-chem--q3

The Ka of the weak acid is:

  • 4.90

  • 8.72

  • 1.26 x 10-5

  • 1.91 x 10-9

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41 mark

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 ℃ is: 

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

  • 1.08

  • 4.73

  • 2.91

  • 4.74

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51 mark

The table shows the pKa values for three acids

              Acid               

     pKa         

Benzoic acid

       4.2

Nitrous acid

       3.1

Lactic acid 

       3.4

Which of the following statements is correct? 

  • The Ka value for lactic acid at 25 ℃ is 3.98 x 10-5 mol dm-3

  • The Ka value for nitrous acid at 25 ℃ is 7.94 x 10-4 mol dm-3

  • Nitrous acid is the weakest acid

  • Benzoic acid is the strongest acid

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11 mark

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    21 mark

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      31 mark

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        41 mark

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          51 mark

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            61 mark

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