Question
Catalysts increase the rate of chemical reactions.
(a) Name the type of metals often used as catalysts. [1]
(b) A student investigated the reaction of zinc powder with excess dilute hydrochloric acid in the absence of a catalyst.
$
\mathrm{Zn}+2 \mathrm{HCl} \rightarrow \mathrm{ZnCl}_2+\mathrm{H}_2
$
The student measured the volume of hydrogen gas produced at 10 second intervals. The graph shows the results.
Answer these questions using information from the graph.
(i) Deduce the volume of hydrogen produced in the first 25 seconds of the experiment.
volume = ………………………… cm3[1]
(ii) Explain why no more hydrogen is produced after 50 seconds. ……………………………………………………………………………………………………………………… [1]
(iii) The experiment is repeated using a catalyst.
Draw a line on the grid to show how the volume of hydrogen changes with time when a catalyst is used.
All other conditions stay the same. [2]
(iv) Describe what effect the following changes have on the rate of the reaction.
- The concentration of hydrochloric acid is decreased.
All other conditions stay the same.
- Large pieces of zinc are used.
All other conditions stay the same. [5]
(c) (i) Describe a test for hydrogen.
test………………………….
result……………………………….. [3]
(ii) State one use of hydrogen. [1] [Total: 10]
▶️Answer/Explanation
Ans:
(a) transition (elements)
(b)(i) $70 \mathrm{~cm}^3$
(b)(ii) the reaction has finished / all the zinc has been used up 1
(b)(iii) Line starts at 0, 0 and steeper gradient (1)
Line levels out at 96 cm3 hydrogen and before the line already on the grid (1)
(b)(iv) concentration: (rate) decreases / gets slower (1)
particle size: (rate) decreases / gets slower (1)
(c)(i) lighted splint (1)
pops / explodes (1)
(c)(ii) fuel
Question
A teacher passed hydrogen gas over hot copper(II) oxide.
\(CuO(s) + H_2(g) → Cu(s) + H_2O(g)\)
(a) Which substance is reduced in this reaction?
Explain your answer.
…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….. [2]
(b) The diagram shows the apparatus used.
The hydrogen was passed over the hot copper(II) oxide until the reaction was complete.
(i) As the experiment proceeds, suggest what happens to the mass of copper(II) oxide.
……………………………………………………………………………………………………………….. [1]
(ii) Suggest why electrical heating is used in this experiment and not a Bunsen burner.
……………………………………………………………………………………………………………….. [1]
(iii) Describe the chemical test for the presence of water.
test…………………………………………………………………………………………………………..
result……………………………………………………………………………………………………….. [2]
[Total: 6]
Answer/Explanation
(a)
copper(II) oxide;
loses oxygen;
(b)(i) (mass of copper oxide in tube) decreases; 1
(b)(ii) hydrogen is flammable/ hydrogen is explosive; 1
(b)(iii) anhydrous copper(II) sulfate goes blue/white copper(II) sulfate goes blue
(1 mark for anhydrous copper (II) sulfate/white copper(II) sulfate)
OR
anhydrous cobalt(II) chloride goes pink / blue cobalt(II) chloride goes pink
(1 mark for anhydrous cobalt(II) chloride/ blue cobalt(II) chloride)