Changing the surface area of the reactants
4 marks · NormalSolid magnesium ribbon reacts with dilute sulfuric acid to produce hydrogen gas. A student wants to investigate how changing the surface area of magnesium affects the rate of reaction.
Describe a change the student could make to increase the surface area of magnesium used.
Explain how this change affects the rate of the reaction.
State one variable other than surface area that should be kept constant in this investigation.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Cut the ribbon into smaller pieces or file it into powder. · must show Physical change increases surface area
(b) The reaction rate increases because there are more particles of magnesium exposed, so more collisions with acid particles can occur, making the reaction faster. · must show Greater surface area means more collisions, Faster reaction
(c) Keep the concentration of sulfuric acid constant (alternatively: temperature, volume of acid, or mass of magnesium). · must show Any correct control variable
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Describes increasing surface area, e.g. cut/scrape/grind magnesium, or use powder.
B2 (b) · 1 mark · Explains that more particles are exposed for reaction/as surface area increased.
B3 (b) · 1 mark · Explains that reaction rate increases as frequency of collisions increases.
B4 (c) · 1 mark · States a valid constant variable, e.g. acid concentration, temperature, volume, or mass of magnesium.
Worked solution
a) The student could cut the magnesium ribbon into smaller pieces or use magnesium powder to increase the surface area.
b) Increasing the surface area exposes more magnesium particles to the acid, so more collisions occur per second and the reaction happens more quickly.
c) The concentration of sulfuric acid should be kept constant (alternatively: temperature, acid volume, or mass of magnesium).