DP Chemistry (last assessment 2024)

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Question 18M.2.hl.TZ2.2

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Date May 2018 Marks available [Maximum mark: 8] Reference code 18M.2.hl.TZ2.2
Level hl Paper 2 Time zone TZ2
Command term Calculate, Deduce, Formulate, Outline, Predict Question number 2 Adapted from N/A
2.
[Maximum mark: 8]
18M.2.hl.TZ2.2

Graphing is an important tool in the study of rates of chemical reactions.

(d.i)

The graph represents the titration of 25.00 cm3 of 0.100 mol dm−3 aqueous ethanoic acid with 0.100 mol dm−3 aqueous sodium hydroxide.

M18/4/CHEMI/HP2/ENG/TZ2/02.d.i_01

Deduce the major species, other than water and sodium ions, present at points A and B during the titration.

 

[2]

Markscheme

A: CH3COOH/ethanoic/acetic acid AND CH3COO–/ethanoate/acetate ions

B: CH3COO–/ethanoate/acetate ions

 

Penalize “sodium ethanoate/acetate” instead of “ethanoate/acetate ions” only once.

[2 marks]

(d.ii)

Calculate the pH of 0.100 mol dm−3 aqueous ethanoic acid.

Ka = 1.74 × 10−5

[2]

Markscheme

K a = 1.74 × 10 − 5 = [ H + ] 2 0.10

OR

[H+] = 1.32 × 10–3 «mol dm–3»

«pH =» 2.88

 

Accept [2] for correct final answer.

[2 marks]

(d.iii)

Outline, using an equation, why sodium ethanoate is basic.

[1]

Markscheme

«forms weak acid and strong base, thus basic»

CH3COO–(aq) + H2O(l) ⇌  CH3COOH(aq) + OH–(aq)

 

Accept → for ⇌ .

[1 mark]

(d.iv)

Predict whether the pH of an aqueous solution of ammonium chloride will be greater than, equal to or less than 7 at 298 K.

[1]

Markscheme

less than 7

[1 mark]

(e.i)

Formulate the equation for the reaction of nitrogen dioxide, NO2, with water to form two acids.

[1]

Markscheme

2NO2(g) + H2O(l) → HNO2(aq) + HNO3(aq)

[1 mark]

(e.ii)

Formulate the equation for the reaction of one of the acids produced in (e)(i) with calcium carbonate.

[1]

Markscheme

2HNO2(aq) + CaCO3(s) → Ca(NO2)2(aq) + CO2(g) + H2O(l)

OR

2HNO3(aq) + CaCO3(s) → Ca(NO3)2(aq) + CO2(g) + H2O(l)

[1 mark]

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