A student added 5 grams of calcium chloride, a white solid substance, to 15 grams of water at 220 C. Several observations were made and the student inferred that a chemical reaction occurred. Which observation best supports the student's inference that a chemical reaction occurred?

D

Explanation:

A The calcium chloride dissolves in solution

B The mass of the solution totals 20 g

C The temperature of the solution is 35 degrees

D The solution became lighter in color

The correct answer would be that the solution became lighter in color.

An increase in temperature can also be considered a sign of a chemical reaction but in this case, the dissolution of calcium chloride in water is in itself exothermic.

A change in the mass of the final solution could also be considered a sign of a chemical reaction but in this case, the total mass equals the addition of the individual masses of the reactant.

The dissolution of calcium chloride in water is not enough as evidence of a chemical reaction. Dissolution can be a physical change of which, the evaporation of the water would retrieve the solute.

A change in color, however, is one of the evidence to establish that a chemical reaction has occurred.

The correct option is D.