Properties of Matter — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. A student heats sugar in a pan. The sugar turns brown and gives off a smell. Which statement best explains what happened?
A) A physical change occurred because the sugar simply melted into a liquid.
B) A chemical change occurred because the brown color and new odor indicate a new substance formed.
C) A physical change occurred because heating always causes physical changes.
D) A chemical change occurred because all changes caused by heat are chemical changes.
Color change and new odor are signs of a chemical change (caramelization). A new substance is formed.
2. A scientist mixes two clear liquids together and a yellow solid appears at the bottom of the beaker. What type of change is this?
A) A physical change because both liquids were clear before mixing.
B) A physical change because the solid can be filtered out of the mixture.
C) A chemical change because a precipitate forming indicates a new substance was created.
D) A chemical change because all mixing of liquids produces chemical reactions.
A precipitate (solid forming from liquid) is a sign of a chemical reaction producing a new substance.
3. A student dissolves salt in warm water. The water tastes salty but looks clear. Which conclusion is correct?
A) A chemical change occurred because the salt disappeared into the water.
B) A physical change occurred because the salt and water can be separated by evaporation.
C) A chemical change occurred because the taste of the water changed.
D) A physical change occurred because the water changed from clear to salty.
Dissolving salt is physical — salt stays NaCl and can be recovered by evaporating the water.
4. A nail left outside for several weeks develops an orange coating. Which evidence best supports that this is a chemical change?
A) The nail changed shape as the coating built up on its surface.
B) A new substance called iron oxide formed with different properties than iron.
C) The nail became heavier because it absorbed water from the rain.
D) The orange color is just dirt that stuck to the surface of the nail.
Rust (iron oxide) is chemically different from iron — new substance, different color and properties.
Part B: Fill in the Blank
Write the correct answer on each line.
1. When a new color appears during a reaction, it is evidence that a chemical change occurred.
Color change (that isn't due to mixing paint colors) often indicates new substances are forming.
2. A change that can easily be reversed, like melting ice, is usually a physical change.
Physical changes are generally reversible (melt → freeze; dissolve → evaporate). Chemical changes usually are not.
3. The formation of gas bubbles during a reaction often signals a chemical change.
Gas production (like CO₂ bubbles when baking soda meets vinegar) is a key indicator of a chemical reaction.
4. A solid that forms when two liquids are mixed together is called a precipitate.
A precipitate is an insoluble solid product that forms during a chemical reaction in a liquid solution.
5. If a substance gives off heat or light during a change, it is likely a chemical reaction.
Energy release (heat or light) during a change — especially when no outside energy was added — signals a chemical reaction.