DP Chemistry (last assessment 2024)

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Question 18M.2.sl.TZ1.4

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Date May 2018 Marks available [Maximum mark: 4] Reference code 18M.2.sl.TZ1.4
Level sl Paper 2 Time zone TZ1
Command term Outline, Show, Suggest Question number 4 Adapted from N/A
4.
[Maximum mark: 4]
18M.2.sl.TZ1.4

Calcium carbonate reacts with hydrochloric acid.

CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)

(a)

Outline two ways in which the progress of the reaction can be monitored. No practical details are required.

[2]

Markscheme

Any two of:

loss of mass «of reaction mixture/CO2»

«increase in» volume of gas produced

change of conductivity

change of pH

change in temperature

 

Do not accept “disappearance of calcium carbonate”.

Do not accept “gas bubbles”.

Do not accept “colour change” or “indicator”.

[2 marks]

The results of a series of experiments in which the concentration of HCl was varied are shown below.

M18/4/CHEMI/SP2/ENG/TZ1/04.b

(b.i)

Suggest why point D is so far out of line assuming human error is not the cause.

[1]

Markscheme

reaction is fast at high concentration AND may be difficult to measure accurately

OR

so many bubbles of CO2 produced that inhibit contact of HCl(aq) with CaCO3(s)

OR

insufficient change in conductivity/pH at high concentrations

OR

calcium carbonate has been used up/is limiting reagent/there is not enough calcium carbonate «to react with the high concentration of HCl»

OR

HCl is in excess

OR

so many bubbles of CO2 produced that inhibit contact of HCl(aq) with CaCO3(s)

[1 mark]

(b.ii)

Suggest the relationship that points A, B and C show between the concentration of the acid and the rate of reaction.

[1]

Markscheme

«directly» proportional

 

Accept “first order” or “linear”.

Do not accept “rate increases as concentration increases” or “positive correlation”

[1 mark]

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