Questions: Signs of Chemical Change

Question 1

You mix baking soda and vinegar in a cup. It fizzes, bubbles up, and the cup feels cold. Which signs suggest a chemical change occurred?

• A. Only the fizzing — bubbles always mean a chemical change
• B. Only the temperature change — getting cold means new substances formed
• C. Both the gas bubbles (fizzing) and the temperature change together — multiple signs point to a chemical change
• D. Neither — this is just a physical change because nothing changed color

Answer: (C)

The fizzing (gas production) and the temperature change are both signs of a chemical change. The baking soda and vinegar react to form new substances, including carbon dioxide gas (the bubbles). You do not need a color change for it to be chemical — multiple other signs can confirm it. One sign alone can be misleading, but multiple signs together make a strong case.

Question 2

Mixing red paint and blue paint to make purple paint is a chemical change because the color changed.

• T. True
• F. False

Answer: False

False. Mixing paints is a physical change — you are just combining two substances that blend their colors. No new substance is created. The red pigment and blue pigment are both still there. A chemical color change involves a substance transforming into a new substance with a different color, like an apple turning brown when cut.

Question 3

Name three signs that a chemical change might be happening.

Model answer: Any three of: unexpected color change, gas bubbles or fizzing (when not boiling), temperature change without external heating or cooling, new smell, light production, or a solid forming in a clear liquid.

These signs indicate that new substances are being formed. No single sign is proof by itself — boiling water produces bubbles but is not a chemical change. But when you see multiple signs together, especially ones you did not cause by heating or mixing colors, a chemical change is very likely occurring.