Year 7 Science · Unit 2 · Lesson 13
Apply Worksheet
Learning Goals
Compare two (and three!)
Complete the table to compare an element, a compound and a mixture. Use your lesson notes to fill in all cells.
| Feature | Element | Compound | Mixture |
|---|---|---|---|
| Made of… | |||
| Example | |||
| Can be separated physically? | |||
| Fixed or variable composition? | |||
| Pure substance or not? |
Predict + reason
Scenario
A scientist analyses an unknown white solid labelled "Substance X." The tests show:
• It melts at exactly 801 °C every time it is tested.
• When dissolved in water, the solution conducts electricity.
• It cannot be separated into simpler parts by filtering or evaporation.
• Its formula is NaCl.
(a) Predict whether Substance X is an element, a compound, or a mixture. Write your prediction clearly.
(b) Justify your prediction using at least three pieces of evidence from the scenario. For each piece of evidence, name the Unit 2 concept it relates to.
(c) A student wants to find out whether more sugar dissolves in hot water than in cold water. Identify the independent variable, the dependent variable, and one variable they must keep controlled.
1. Explain why dissolving salt in water is a physical change and no new substance is made. Use the particle model in your answer, and describe how you could get the salt back unchanged.
Wrap Up
In one sentence, what was the main idea of this lesson?