What is being taught lesson by lesson:

Key Terms for this topic (Tier 3 vocabulary)

Acid -alkali – base – neutralisation – dissociation – reactivity – displacement – ore – native – reduction – oxidation – electrolysis – electrode – electrolyte – aqueous – bauxite – cryolite.

Chemical Changes

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What everyone needs to know:

Metals react with oxygen to produce metal oxides. This is the most basic example of oxidation. Loss of this oxygen is called reduction.

The reactivity series is an order of how vigorous metals react. We put hydrogen and carbon in as reference points to other reactions. More reactive metals can displace less reactive ones from a compound.

You need to describe what would happen with the metals on the reactivity series if put in water or acid at room temperature as well a remembering the order of this series.

Reduction is a process of extracting metals from their ores (removing the oxygen). This is mostly the reduction using carbon such as in the blast furnace.

  • Metal + Acid → Salt + Hydrogen
  • Acid + Alkali → Salt + Water
  • Metal oxide + Acid → Salt + Water
  • Acid + Metal carbonate → Salt + Water + Carbon dioxide

During reactions with acids to make salts: hydrochloric acid makes chlorides, phosphoric acid makes phosphates, sulfuric acid makes sulfates and nitric acid makes nitrates. Using this, you should be able to predict the name of the salt being made and given a required salt, choose reactants that will make that salt.

Required practical 8 – Use an insoluble carbonate or oxide, reacted with an acid to produce a dry and pure soluble salt.

Acids produce H+ ions and alkalis produce OH ions. Their concentration links to the pH scale of 0-14 which can be measured using universal indicator or a pH probe. Neutralisation is shown by the half equation below:

H+(aq) + OH(aq) → H2O(l)

Strong acids are fully dissociated of ionised. 100% of potential H+ ions are released into solution (nitric or sulfuric acids). In weak acids, only a tiny proportion are (ethanoic or citric acids). Don’t mix dilute and concentrated with weak and strong.

Electrolysis is using a DC electric current to split a compound up into elements. A solution or molten substance undergoing this process is called an electrolyte. Positive ions move towards the negative electrode (cathode) and positive ions move towards the negative electrode (anode). There they change from ions to elements.

To remove elements from ores that are more reactive than carbon, we use electrolysis. Aluminium is the best example, it is melted and electrolysed. It is a very expensive process using lots of heat and electricity. Cryolite is added to lower the melting point of aluminium oxide (found in the ore bauxite). The electrodes are carbon (graphite).

When electrolysing a solution, the least reactive ions return to being elements. At the anode (-) hydrogen is given off if the metal is more reactive than hydrogen. At the cathode (+) oxygen is released unless there is a halogen in the solution, in which case it will be released (Cl2, Br2, I2). The oxygen and hydrogen come from the water itself. You should be able to predict what is going to be formed.

Required practical 9 – investigate and predict the products while electrolysing aqueous solutions.

Extra topics needed for the Higher papers:

Oxidation and reduction needs to be explained in terms of gaining and losing electrons. Relate reactions and their half equations to REDOX using OILRIG. Identify ions that are oxidised or reduced and identify spectator ions.

Describe the acid reaction with metals in terms of electrons (identify REDOX).

Write balanced ionic half equations for the reactions happening at both electrodes in all reactions. These include:

2H+ + 2e → H2

4OH → O2 + 2H2O + 4e

4OH + 4e → O2 + 2H2O