A student in Jamaica investigated the effect of concentration on reaction rate by reacting magnesium ribbon with different concentrations of hydrochloric acid. She kept the temperature, length of magnesium ribbon, and volume of acid constant. Why was it important to keep these variables constant?

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Question

A student in Jamaica investigated the effect of concentration on reaction rate by reacting magnesium ribbon with different concentrations of hydrochloric acid. She kept the temperature, length of magnesium ribbon, and volume of acid constant. Why was it important to keep these variables constant?

Accepted Answer

To ensure that only concentration affects the rate being measured — Award 1 mark for B. In a fair test, only the independent variable (concentration) should change; all other variables must be controlled so that any change in rate can be attributed to concentration alone. A is incorrect — time is not the reason for controlling variables. C is incorrect — cost is not a scientific reason. D is incorrect — complete dissolution is not the purpose of controlling variables.

Answer

To ensure that only concentration affects the rate being measured

Answer

To make sure the magnesium completely dissolves

Answer

To make the experiment faster to complete

Answer

To reduce the cost of chemicals used

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