Properties of Matter — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. The law of conservation of mass states that matter cannot be created or destroyed.
Conservation of mass: mass before a reaction = mass after a reaction. Matter is neither created nor destroyed.
2. In any chemical reaction the total mass before the reaction equals the total mass after.
The law of conservation of mass: total mass before = total mass after, in any closed system.
3. When wood burns, the mass of the ash plus the mass of the gases equals the mass of the original wood.
Burning produces ash (solid) + CO₂ and water vapor (gases). All products together equal the original mass.
4. A physical change alters the appearance or state of matter but not its chemical makeup.
Physical changes affect size, shape, or state — the material looks different but remains the same substance.
5. A chemical change produces a new substance with different properties than the original.
New substances formed in chemical changes have different properties (color, smell, state, reactivity) than the reactants.
6. Melting, freezing, and evaporating are all examples of physical changes.
State changes (solid↔liquid↔gas) are physical changes — same substance, different state.
7. Rusting occurs when iron reacts with oxygen and water to form iron oxide.
Rust = iron oxide (Fe₂O₃). It forms when iron reacts with oxygen and moisture — a chemical change.
8. The total mass of reactants always equals the total mass of products in a closed system.
Conservation of mass: reactants → products, with equal total mass on both sides.
9. Measuring the mass of an object before and after a change helps prove conservation of mass.
By measuring mass before and after, you can verify that no mass was created or destroyed.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
Ice melting
→ Physical change — solid water becomes liquid water but stays H₂O
Physical change — salt particles mix with water but remain salt
Baking soda and vinegar
→ Chemical change — produces carbon dioxide gas and a new compound
Physical change — solid water becomes liquid water but stays H₂O
Dissolving salt
→ Physical change — salt particles mix with water but remain salt
Chemical change — iron combines with oxygen to form a new substance
Iron rusting
→ Chemical change — iron combines with oxygen to form a new substance
Chemical change — produces carbon dioxide gas and a new compound
Ice melting=physical H₂O stays same(idx1); Baking soda+vinegar=chemical CO₂ gas new compound(idx3); Dissolving salt=physical salt stays same(idx0); Iron rusting=chemical new substance(idx2)