C3 2019

Question 1

Sodium thiosulfate reacts with dilute hydrochloric acid as shown.
Na2S2O3(aq) + 2HCl(aq) → 2NaCl(aq) + SO2(g) + S(s) + H2O(l)
Give the simplest ionic equation for this reaction.

Answer 1

S2O32– + 2H+ -> SO2 + S + H2O

Question 2

The gas SO2 is a pollutant.
State the property of SO2 that causes pollution when it enters rivers.
Give an equation to show the reaction of SO2 with water.

Answer 2

acid(ic)
SO2 + H2O -> H2SO3

Question 3

The initial rate of the reaction between sodium thiosulfate and hydrochloric acid can be monitored by measuring the time taken for a fixed amount of sulfur to be produced.
Describe an experiment to investigate the effect of temperature on the initial rate of
this reaction.
Include
* a brief outline of your method
* how you will measure the time taken for a fixed amount of sulfur to be formed
* how you will present your results in graphical form
* a sketch of the graph that you would expect.

Answer 3

Stage 1 Method
(1a) Idea of using disappearing cross or
colorimetry
(1b) Puts acid into container on
cross
(1c) Add second reactant and start timing

Stage 2 Measurements
(2a) Repeat at different temperatures
(2b) Record time, t, for cross to disappear
(2c) Idea of ensuring other variables (cross,
volumes, concentrations) kept constant

Stage 3 Use of Results
(3a) 1/t is a measure of rate
(3b) plot of rate (y-axis) against T (xaxis)
(3c) sketch of plot as shown (exponential)

Question 4

In aqueous solution, sulfuric acid acts as a strong acid. The H2SO4 dissociates to form
HSO4− ions and H+ ions.
The HSO4− ions act as a weak acid and dissociate to form SO42− ions and H+ ions.
Give an equation to show each stage in the dissociation of sulfuric acid in
aqueous solution.
Include appropriate arrows in your equations

Answer 4

H2SO4 -> HSO4– + H+
HSO4– ⇌ SO42– + H+

Question 5

A student is required to make 250 cm3 of an aqueous solution that contains an
accurately measured mass of sodium hydrogensulfate (NaHSO4).
Describe the method that the student should use to make this solution.

Answer 5

M1 weigh solid and transfer using a method that allows exact mass
to be known

M2 dissolve in water in suitable container

M3 transfer with washings into 250 cm3
volumetric flask

M4 make up to mark / 250 cm3 AND THEN shake / invert / mix

Question 6

State the change that needs to be made to the apparatus in Figure 1 to allow the cell
reaction to go to completion.

Answer 6

Replace voltmeter for a lamp

Question 7

Give the equation for the reaction between iron and sulfuric acid.

Answer 7

Fe + H2SO4  FeSO4 + H2