Propanoic acid (C2H5COOH) is a weak acid.
1.
The acid dissociation constant (Ka) for propanoic acid is 1.35 × 10–5 mol dm–3 at 25 oC
(a) State the meaning of the term weak acid.
___________________________________________________________________
___________________________________________________________________
(1)
(b) Give an expression for the acid dissociation constant for propanoic acid.
Ka
(1)
(c) A student dilutes 25.0 cm3 of 0.500 mol dm–3 propanoic acid by adding water until the total
volume is 100.0 cm3
Calculate the pH of this diluted solution of propanoic acid.
Give your answer to 2 decimal places.
pH _______________
(4)
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, (d) A buffer solution with a pH of 4.50 is made by dissolving x g of sodium propanoate
(C2H5COONa) in a solution of propanoic acid. The final volume of buffer solution is
500 cm3 and the final concentration of the propanoic acid is 0.250 mol dm–3
Calculate x in g
For propanoic acid, Ka = 1.35 × 10–5 mol dm–3
x _______________ g
(6)
(Total 12 marks)
Which statement about pH is correct?
2.
A The pH of a weak base is independent of temperature.
B At temperatures above 298 K, the pH of pure water is less
than 7.
C The pH of 2.0 mol dm–3 nitric acid is approximately 0.30
D The pH of 0.10 mol dm–3 sulfuric acid is greater than that of
0.10 mol dm–3 hydrochloric acid.
(Total 1 mark)
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, A 0.10 mol dm–3 aqueous solution of an acid is added slowly to 25 cm3 of a 0.10 mol dm–3
3.
aqueous solution of a base.
Which acid–base pair has the highest pH at the equivalence point?
A CH3COOH and NaOH
B CH3COOH and NH3
C HCl and NaOH
D HCl and NH3
(Total 1 mark)
Which is the concentration of NaOH(aq), in mol dm–3, that has pH = 14.30?
4.
Kw = 1.00 × 10–14 mol2 dm–6 at 25 °C
A –1.16
B 5.01 × 10–15
C 2.00 × 1014
D 2.00
(Total 1 mark)
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, This question is about different pH values.
5.
(a) For pure water at 40 °C, pH = 6.67
A student thought that the water was acidic.
Explain why the student was incorrect.
Determine the value of Kw at this temperature.
Explanation _________________________________________________________
___________________________________________________________________
Kw _________________________ mol2 dm–6
(4)
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1.
The acid dissociation constant (Ka) for propanoic acid is 1.35 × 10–5 mol dm–3 at 25 oC
(a) State the meaning of the term weak acid.
___________________________________________________________________
___________________________________________________________________
(1)
(b) Give an expression for the acid dissociation constant for propanoic acid.
Ka
(1)
(c) A student dilutes 25.0 cm3 of 0.500 mol dm–3 propanoic acid by adding water until the total
volume is 100.0 cm3
Calculate the pH of this diluted solution of propanoic acid.
Give your answer to 2 decimal places.
pH _______________
(4)
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, (d) A buffer solution with a pH of 4.50 is made by dissolving x g of sodium propanoate
(C2H5COONa) in a solution of propanoic acid. The final volume of buffer solution is
500 cm3 and the final concentration of the propanoic acid is 0.250 mol dm–3
Calculate x in g
For propanoic acid, Ka = 1.35 × 10–5 mol dm–3
x _______________ g
(6)
(Total 12 marks)
Which statement about pH is correct?
2.
A The pH of a weak base is independent of temperature.
B At temperatures above 298 K, the pH of pure water is less
than 7.
C The pH of 2.0 mol dm–3 nitric acid is approximately 0.30
D The pH of 0.10 mol dm–3 sulfuric acid is greater than that of
0.10 mol dm–3 hydrochloric acid.
(Total 1 mark)
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, A 0.10 mol dm–3 aqueous solution of an acid is added slowly to 25 cm3 of a 0.10 mol dm–3
3.
aqueous solution of a base.
Which acid–base pair has the highest pH at the equivalence point?
A CH3COOH and NaOH
B CH3COOH and NH3
C HCl and NaOH
D HCl and NH3
(Total 1 mark)
Which is the concentration of NaOH(aq), in mol dm–3, that has pH = 14.30?
4.
Kw = 1.00 × 10–14 mol2 dm–6 at 25 °C
A –1.16
B 5.01 × 10–15
C 2.00 × 1014
D 2.00
(Total 1 mark)
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, This question is about different pH values.
5.
(a) For pure water at 40 °C, pH = 6.67
A student thought that the water was acidic.
Explain why the student was incorrect.
Determine the value of Kw at this temperature.
Explanation _________________________________________________________
___________________________________________________________________
Kw _________________________ mol2 dm–6
(4)
Harris Federation - Consultants Page 4 of 42
