EasyChemistryHigh School (9–10)GeneralMixtures and Solutions › Elements, Compounds and ChangesConceptualBoard Exam
Say whether each is a physical or a chemical change, with a reason…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Say whether each is a physical or a chemical change, with a reason.
- Butter melting in a pan
- Bread being toasted until it is brown
- Salt dissolving in water
- A firecracker exploding
- A sheet of glass breaking
- Grass being digested by a cow
Need a reminder? The key ideaShow
A physical change makes no new substance (melting, dissolving, breaking). A chemical change makes new substances (burning, rusting, cooking). Gas, colour, smell, heat, light and a new solid are clues; the test is always: is a new substance made?
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Physical. (a) Melted butter is still butter. (c) The salt can be got back by evaporating the water. (e) The pieces are still glass.
Step 2. Chemical. (b) Toasting makes new brown substances and a new smell. (d) The firecracker makes new gases, with heat, light and sound. (f) Digestion breaks the grass into new substances.
Answer: (a), (c) and (e) are physical; (b), (d) and (f) are chemical.
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