Rates of Reaction
5 marks · EasyThe diagram below shows apparatus used to measure the rate of a reaction between marble chips (calcium carbonate) and dilute hydrochloric acid.
State what happens to the mass reading as the reaction occurs.
Suggest why a cotton wool plug is placed in the neck of the flask.
Describe two different ways to increase the rate of this reaction.
Explain, using collision theory, why increasing the temperature increases the rate of reaction.
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(a) The mass reading decreases
(b) To prevent acid from splashing out while allowing gas to escape
(c) Increase temperature; use more concentrated acid; use smaller marble chips; add a catalyst (any two)
(d) Particles have more energy, move faster; more collisions have energy greater than the activation energy, so rate increases
Common mistakes: Confusing effect of cotton wool; Giving more than one change in a single point for c
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly states that mass decreases as CO2 escapes.
B2 (b) · 1 mark · Explains cotton wool prevents acid spitting out but lets gas escape.
M1 (c) · 1 mark · Gives one way to increase the rate: (increase temp, increase concentration, decrease chip size, add catalyst).
M2 (c) · 1 mark · Gives a different second way.
E1 (d) · 1 mark · Explains temperature increases kinetic energy; more particles have activation energy for successful collisions.
Worked solution
a) The mass reading goes down as CO2 gas escapes during the reaction.
b) The cotton wool stops acid or marble from spitting out but allows the gas to leave the flask.
c) (1) Increase the temperature; (2) Use smaller marble chips (more surface area); other options: increase acid concentration, use a catalyst.
d) At higher temperature, the reactant particles move faster and have more energy. Collisions are more frequent and more have enough energy to react, so the rate increases.