Section 2 e) Summary

When a metal reacts with an acid, it forms a salt and hydrogen. It is easily remembered by MASH
Metal
+
Acid
-->
Salt
+
Hydrogen

When hydrogen reacts with oxygen, it releases a lot of energy in the form of heat and light. This creates a flame, making it a combustion reaction.

2H2 + O2 --> 2H2O + energy

This reaction produces pure water as well as energy. We can test for water in a few different ways:

Testing for water

Physical test: Heat the water and see if it boils at 100℃, in which case it is pure.

Chemical test: Expose to anhydrous copper (II) sulphate, a white substance. It will turn blue in presence of water.

Section 2 e) Key Words

Chemical Test: A test involving the chemical molecules, and the way they react with other molecules. e.g. test for water using anhydrous copper (ii) sulphate.

Combustion: Reaction with oxygen that produces a flame (a lot of heat and light energy is released)

Physical Test: A test involving the physical properties of a molecule, e.g. boiling point of water.

Section 2 e) Specification

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

The rule "MASH" tells us that when a metal reacts with an acid, a salt will be produced, as well as hydrogen.

Metal + Acid --> Salt + Hydrogen

e.g.

Mg(s) + 2HCl(aq) --> MgCl2 + H2

2.26 describe the combustion of hydrogen

The combustion of hydrogen is its reaction with oxygen. It is exothermic, so a lot of energy is produced, as well as pure water.

2H2 + O2 --> 2H2O

2.27 describe the use of anhydrous copper(II) sulfate in the chemical test for water

If anhydrous copper sulphate changes from white to blue, it has become hydrous copper sulphate and it contains water.

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

Heat the water until it boils, with a thermometer. If it boiled at 100℃ exactly, it is pure water.