Page 68 - 新思维科学学生用书7 样章

2.7 Compounds and mixtures

Think like a scientist

Is water really a mixture? safety glasses

You are going to investigate if drinking
water contains anything other than water. tongs water

You will need: evaporating basin
The apparatus shown in the diagram.
gauze
Safety
Wear safety glasses. Take care during tripod
step 2 as the solution may start to spit.

Do not touch the evaporating basin
with your hands – use tongs. Bunsen burner
Read the health and safety notes before you start.

1 Put some water in the evaporating basin and heat it until it boils.
2 Once the water starts to boil, turn the heat down and continue to heat it gently.
3 When you have evaporated off some of the water (or the solution has started to
spit) remove it from the heat.
4 Leave the evaporating basin to cool. The water may take a day or two to

evaporate completely. It will depend on the temperature.
Questions

1 Use ideas about particles to explain why the water evaporated.
2 What was left in the evaporating basin?
3 Where did this substance come from?
4 Was the water you used pure water, or was it a mixture of water and other

substances? Explain your answer.
5 Why did you need to wear safety glasses?

Summary checklist

I can distinguish between a compound and a mixture.

I can explain the difference between a compound and a mixture.
I can give examples of mixtures.

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