Edexcel IGCSE Chemistry Chapter 6, page 51 ANSWERS
1 a) Refer to Fig 7.12 p 58 for a basic apparatus. The reaction could also be carried out in a
conical flask with a side arm and the collecting vessel should be an inverted measuring cylinder
of appropriate capacity to allow the volume of gas evolved to be noted at each time interval.
b)
120
volume (cm3)
100
80
60
40
20
0
0
50
100
150
200
250
300
350
400
time (s)
c) The gas is being evolved most quickly at the start of the reaction (during the first 50
seconds). The concentration of reactants is greatest at this time, so the reaction proceeds most
vigorously because there are more reacting particles present.
d) About 65 seconds (orange lines)
Edexcel IGCSE Chemistry Chapter 6, page 51 ANSWERS
e)
(i)
(ii)
(iii)
(iv)
Initial rate
Less than if using small pieces,
because total surface area exposed to
acid is less.
Since only half the acid particles are
present if the concentration is half of the
original, the reaction rate would be half
of the original rate.
Same as in b) above, but will level off
more rapidly.
More rapid than originally, because the
particles have greater kinetic energy, so
more collisions take place.
Total volume
100 cm
3
50 cm3 because there is only half the
amount of acid available for reaction
50 cm3 because there is only half the
amount of acid available for reaction
100 cm3
2 a) There is no difference in the amount or surface area of magnesium. There is no difference
in total volume of liquid. There are fewer acid particles present because the acid has been
diluted to 80% of the previous concentration. Since there are fewer acid particles, fewer
collisions will take place and the rate of reaction will consequently be slower.
b) The reaction will proceed more quickly since the particles in heated acid are moving faster
than particles in cooler acid. Since particles are moving faster, more collisions take place in a
given time and the rate of reaction is consequently greater.
c) Stirring maintains a high concentration of reacting particles at the reaction site by removing
products formed.
3 a) A catalyst lowers the activation energy of a chemical reaction, so the reaction can proceed
more rapidly than in the absence of the catalyst. The catalyst does this by providing a surface
which brings the reactants close together, so the reaction can take place. The catalyst is not a
reactant, so is unchanged at the end of the reaction.
b) Measure the rate of the reaction by collecting O2 evolved over a specified time in the absence
of CuO. Repeat the experiment in the presence of a known amount of CuO.
The CuO should all be able to be recovered after the reaction, since CuO is insoluble in water.
The mass of CuO should remain unchanged.