MediumChemistryHigh School (9–10)GeneralMixtures and Solutions › Elements, Compounds and ChangesConceptual
For each, name the sign of a chemical change, and the new substance if you can.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
For each, name the sign of a chemical change, and the new substance if you can.
- Baking soda is added to vinegar, and it fizzes.
- A slice of potato turns blue-black when iodine is dropped on it.
- A silver spoon slowly turns black.
- A gas flame on a stove gives out heat and light.
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. (a) A gas is given off: carbon dioxide.
Step 2. (b) A change of colour: iodine forms a new blue-black substance with the starch in the potato.
Step 3. (c) A change of colour: a black layer of silver sulphide forms on the spoon.
Step 4. (d) Heat and light: the gas burns to form carbon dioxide and water.
Answer: (a) gas, (b) colour, (c) colour, (d) heat and light.
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