Question

A scientist compares two samples of white powder. One powder was present at the beginning of an experiment. The other powder was present at the end. She wants to determine whether a chemical reaction has occurred. She finds that neither sample bubbles or dissolves in water. She measures the mass and volume of the solids. Sample one has a volume of 45 cm3 and a mass of 0.5 g. Sample two has a volume of 65 cm3 and a mass of 1.3 g. What should the scientist conclude?
A)The samples have the same color, so no chemical reaction has occurred.
B)The two samples do not react with water, so no chemical reaction has occurred.
C)The densities of the samples are different, so a chemical reaction has occurred.
D)The densities of the samples are the same, so no chemical reaction has occurred.
E)The densities of the samples are different, so no chemical reaction has occurred.

Answer 1

Density of powder 1 = 0.5 g / 45 cm^3 = 1/90 g/cm^3
Density of powder 2 = 1.3 g / 65 cm^3 = 1/50 g/cm^3

Therefore the densities of the two powders are different, hence chemical reaction has occurred.

(note: none of the other choices make sense.  In fact, a different density does not necessarily indicate a chemical change, see paragraph below).

Density of powders are not definitive unless they are each of the same size and texture.  For example, granular sugar, rock sugar, and icing sugar all have different densities.  I would conclude that this experiment does not lend to a reliable answer.