2.28 Describe a physical test to show whether water is pure.

If the water boils at exactly 100 degrees celsius (212 degrees fahrenheit), it is pure.

2.27 Describe the use of anhydrous copper(II) sulfate in the chemical test for water (page 93)

Anhydrous means it has no water, and the initial color (because of this) is white. When water is added, it turns blue.

2.26 Describe the combustion of hydrogen

When hydrogen reacts with oxygen, there is a loud pop, a flame for a split second, and then it's all over. Hydrogen can be produced by reacting a metal with an acid, i.e. magnesium with sulphuric acid.

This reaction produces water...and energy, of course!

Hydrogen + oxygen → water

2.25 Describe the reactions of dilute hydrochloric and dilute sulfuric acids with magnesium, aluminium, zinc and iron

Acid + Metal → Salt + hydrogen

All reactions involve bubbling as hydrogen is released.

Eg
Magnesium + sulphuric acid → magnesium sulphate + hydrogen

EXAM TIP: If it asks for a word equation, state the word equation - you're more likely to get the mark. If you do write a symbol equation, they won't mark it wrong as long as you get it completely correct.