Paige received two 10 mL samples of unknown liquids from her teacher. She combined the substances according to her instructions and recorded the following observations:

Question

1. When the two colorless liquids combined, the color changed to purple.
2. The volume of the combined liquids was 20 mL.
3. The temperature of the liquids rose 10°C after they were combined.
4. The density of the combined liquids was 1.7 g/mL.

Based on her observations, Paige concluded that a chemical reaction took place. Which of her observations support her conclusion?
A.
1 only
B.
1 and 3 only
C.
1, 2, and 3 only
D.
3 and 4 only

Answer 1

To determine which observations support Paige's conclusion that a chemical reaction took place, we can evaluate each observation in the context of evidence for a chemical change.

1. Change in color (Observation 1): The color change from colorless to purple suggests that a new substance was formed, which is a strong indicator of a chemical reaction.

2. Volume change (Observation 2): The volume of the liquid doubled from 10 mL to 20 mL. This by itself does not necessarily indicate a chemical reaction; it could simply be a physical mixing of two liquids.

3. Temperature change (Observation 3): The rise of 10°C indicates that there was an exothermic reaction occurring. Temperature change associated with mixing two substances is often a sign of a chemical reaction.

4. Density (Observation 4): The combined density of 1.7 g/mL does not provide direct evidence that a chemical reaction occurred. While the density of the mixture might change, it can also change due to physical mixing.

Based on the above analysis, the observations that indicate a chemical change are primarily the color change and the temperature change (observations 1 and 3).

Thus, the correct answer is B. 1 and 3 only.