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

The control variable in any experiment is designed in order to apply the same steps of the experiment but with no change happens in the observations.

In this experiment, the student tries to know the effect of solubility of different water-soluble salts (NaCl, CaCl2 and KCO3) on the melting point of the solution. All these salts dissolve in water and give some effect on the melting point except for the sand as the sand doesn't dissolve in water.