Ionic Compounds and the Extraction of Metals: Quick Revision

A brief note on Ionic Compounds and the Extraction of Metals. Read it before a test. Try each question at the end before you open its answer.

Ionic compounds

• A metal atom loses its outer electrons: $\text{Na} \rightarrow \text{Na}^+$, $\text{Mg} \rightarrow \text{Mg}^{2+}$.
• A non-metal atom gains electrons to make eight: $\text{Cl} \rightarrow \text{Cl}^-$, $\text{O} \rightarrow \text{O}^{2-}$.
• The opposite ions attract: an ionic bond. The charges in a formula cancel.
• Properties: hard, brittle crystals; high melting points; dissolve in water; conduct only when melted or dissolved.

Getting metals out

Copper is refined by electrolysis: impure copper anode, pure copper cathode, impurities fall as anode mud.

A worked example

What mass of zinc comes from $32.4\ \text{g}$ of zinc oxide? $\text{ZnO} + \text{C} \rightarrow \text{Zn} + \text{CO}$. Use $\text{Zn} = 65$ and $\text{O} = 16$.

1. Molar mass. $\text{ZnO} = 81\ \text{g/mol}$.
2. Moles. $\dfrac{32.4\ \text{g}}{81\ \text{g/mol}} = 0.4\ \text{mol}$.
3. Zinc. $0.4\ \text{mol} \times 65\ \text{g/mol} = 26\ \text{g}$.

Practice with new numbers

A program to try

The program chooses the method for four metals and works out the worked example.

Mistakes to avoid

• Saying solid salt conducts. Its ions cannot move until it melts or dissolves.
• Calling NaCl a molecule. It is a lattice of ions.
• Reducing aluminium oxide with carbon. Aluminium is more reactive than carbon.
• Mixing up roasting and calcination. Roasting is for sulphides, calcination for carbonates.

Check yourself

1. What is the charge on a sulphide ion?

2. In the refining of copper, which electrode collects the pure copper?

3. What is calcination?

4. Name an ore of mercury.