A student investigates how the size of marble chips (calcium carbonate) affects the rate at which they react with dilute hydrochloric acid. In one experimen...
Question 1 Report
A student investigates how the size of marble chips (calcium carbonate) affects the rate at which they react with dilute hydrochloric acid. In one experiment large chips are used and in another experiment small chips of the same total mass are used.
(a) Name the independent variable, that is the variable the student changes. [1]
(b) Name three variables that must be kept the same so that the experiment is a fair test. [3]
(c) Name a suitable piece of apparatus for measuring the volume of gas given off during the reaction. [1]
Answer Details
This tests the idea of a fair test in a rate-of-reaction experiment: change only one variable and control the rest, then measure the effect.
(a) The independent variable, the one deliberately changed, is the size (surface area) of the marble chips. [1] Smaller chips have a larger surface area for the same mass, so they react faster.
(b) Any three control variables, for example: the volume of acid, the concentration of the acid, the temperature, the total mass of marble, and using the same acid. [3] Keeping these constant makes sure any difference in rate is caused only by the chip size.
(c) The volume of gas can be measured with a gas syringe (an inverted measuring cylinder or burette filled with water is also accepted). [1]
Exam tip: only one variable may change at a time; if two things change you cannot tell which one caused the different rate.
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