Question

A student is investigating the affect of different salts on melting points. Four patches of ice of equal size are roped off and a different type of salt is poured on each, one receives table salt (NaCl), one receives Calcium Chloride (CaCl2), one receives Potassium Carbonate (KCO3) and the fourth receives inert sand instead. Each patch receives an equal amount of salt or sand. The student measures the volume of ice remaining and subtracts it from the original volume of ice to see how much melted away. What is a control variable in this experiment?

Answer 1

Answer: Fourth one which received inert sand.

Explanation:

A control variable is the one which remains unchanged in an experiment. It does not receive any treatment. It is considered as a benchmark or standard for comparison of changes occurring in the dependent or experimental variable.

According to the given situation, the fourth one is the correct option as the inert sand will not have any effect over the melting of ice. This can be useful for comparison of the effect of salts on the ice.

Answer 2

Answer:

The inert sand

Explanation:

A control variable is the variable in which the experiment does not depend on. The outcome of the control variable does not in any way validate or invalidate an experimental procedure.

The student seeks to investigate the effect of different salts on melting point. He used NaCl, CaCl₂, K₂CO₃ and inert sand. The first three are salts. Sand is made up of silica, SiO₂ and it is not a salt. Therefore, the control variable here is the inert sand. Sand is highly unreactive and would not in any significant way help the investigation.