Chemistry HL (FE2016)
Paper 2
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Chemistry HL (FE2016)
Available time 20 Minute(s)
01

A 25.0 cm3 solution of a weak monoprotic acid, HA(aq), is titrated with 0.155 moldm−3 sodium hydroxide, NaOH(aq), and the following graph is obtained.

Paper 2
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Available time 20 Minute(s)
01. Question
Level Hard
Maximum Mark 16
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A 25.0 cm3 solution of a weak monoprotic acid, HA(aq), is titrated with 0.155 moldm−3 sodium hydroxide, NaOH(aq), and the following graph is obtained.

0.100 mol of ammonia, NH3,  was dissolved in water to make 1.00 dm3 of solution. This solution has a hydroxide ion concentration of 1.28×10−3 moldm−3.

(a) (i) Determine the pH at the equivalence point.

[Marks: 1]

(a) (ii) Explain, using an equation, why the equivalence point is not at pH=7.

[Marks: 2]

(a) (iii) Calculate the concentration of the weak acid before the addition of any NaOH(aq).

[Marks: 1]

(a) (iv) Estimate, using data from the graph, the dissociation constant, Ka, of the weak acid, HA, showing your working.

[Marks: 2]

(a) (v) Suggest an appropriate indicator for this titration.

[Marks: 1]

(b) Describe qualitatively the action of an acid-base indicator.

[Marks: 2]

(c) (i) Explain what is meant by the term buffer solution.

[Marks: 1]

(c) (ii) Calculate the pH of a solution prepared by mixing 50.0 cm3 of 0.200 moldm−3 CH3COOH(aq) and 50.0 cm3 of ,0.100 moldm−3 NaOH(aq) showing your working.

[Marks: 2]

(c) (iii) Determine the pH of the solution.

 

[Marks: 2]

(c) (iv) Calculate the base dissociation constant, Kb, for ammonia.

[Marks: 2]
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