Properties of Matter — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
Melting ice is a chemical change because the ice turns into a completely different substance.
Corrected: Melting ice is a physical change because the water molecules stay the same even though the state changes.
The corrected sentence is: "Melting ice is a physical change because the water molecules stay the same even though the state changes.". The original sentence "Melting ice is a chemical change because the ice turns into a completely different substance." contained an error that needed to be fixed.
2. Fix the sentence:
Cutting paper is a chemical change because the paper looks different after you cut it.
Corrected: Cutting paper is a physical change because the paper is still paper even though its shape changed.
The corrected sentence is: "Cutting paper is a physical change because the paper is still paper even though its shape changed.". The original sentence "Cutting paper is a chemical change because the paper looks different after you cut it." contained an error that needed to be fixed.
3. Fix the sentence:
Baking a cake is a physical change because you can still see the flour and eggs.
Corrected: Baking a cake is a chemical change because heat causes the ingredients to form a new substance.
The corrected sentence is: "Baking a cake is a chemical change because heat causes the ingredients to form a new substance.". The original sentence "Baking a cake is a physical change because you can still see the flour and eggs." contained an error that needed to be fixed.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. In a physical change, no new substance is formed and the material stays the same.
Physical changes alter shape, size, or state but the material's chemical identity remains unchanged.
2. Bubbles forming during a reaction can be a sign of a chemical change.
Gas production (bubbles) is one indicator of a chemical change — new substances are being formed.
3. Dissolving sugar in water is a physical change because the sugar molecules remain the same.
The sugar molecules don't change — they just spread out in the water. The process is reversible by evaporation.
4. Burning wood produces ash and smoke, which shows that a chemical change has occurred.
Burning (combustion) creates new substances: ash, carbon dioxide, and water vapor — definite chemical change.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. List three signs that a chemical change has taken place.
Sample answer: Three signs of a chemical change are a color change, gas bubbles being produced, and a temperature change such as the mixture getting warmer or cooler without being heated.
Other signs: formation of a precipitate, production of light, or a new odor.
2. Explain why freezing water is a physical change even though it looks very different from liquid water.
Sample answer: Freezing water is a physical change because the water molecules do not change into a different substance. The molecules simply slow down and arrange into a solid structure, but they are still water molecules.
State changes (solid, liquid, gas) are physical changes. The chemical formula stays the same.