2.28 describe a physical test to show whether water is pure

If the substance you are testing boils at 100ºC and/or freezes at 0ºC, it is pure water

2.26 describe the combustion of hydrogen

If hydrogen is burnt in air, water is produced (initially as water vapour, as it is hot, but later condenses to water if cooled)

The equation for this reaction is  2H₂+ O₂ → 2H₂O

2.25 describe the reactions of dilute hydrochloric acid and dilute sulphuric acids with magnesium, aluminium, zinc and iron

Acid + metal ---> salt + hydrogen


Magnesium

- Reacts vigorously with cold dilute acids
- Produces lots of bubbles


Aluminium

- Little reaction with cold dilute acids (as it has a protective aluminium oxide layer)
- Reacts vigorously with warm dilute acids and produces lots of bubbles


Zinc

- React slowly with dilute acids but more strongly if you heat them up


Iron

Same reactions as zinc.

NOTE: The more reactive the metal, the faster the reaction. For example, very creative metals (such as sodium) will react explosively, as the reaction is very quick. The speed of reaction is given off by the amount of bubbles that are given off.