Page 137 - Chemistry_Form_2

Chemistry
for Secondary Schools

Combustion tube Red-hot iron wire or steel wool

To fume cupboard
Chlorine gas
FOR ONLINE READING ONLY

Heat

Condensed FeCl 3
Cold water
Concentrated H 2SO 4

Figure 5.14: Set-up of the direct preparation of iron(III) chloride

Preparation of insoluble salts
Insoluble salts are prepared by using ionic precipitation or a double decomposition
method. In this method, two soluble salts are used to form an insoluble salt and
a soluble salt. The insoluble salt precipitates, while the soluble salt remains in
solution. The precipitate is filtered and washed with distilled water and then
dried. For example, to prepare insoluble lead(II) iodide, the solution containing
lead ions and another containing iodide ions are mixed. Such solutions could be
lead(II) nitrate and potassium iodide. A bright yellow precipitate of lead(II) iodide
is formed after mixing. The chemical equation for this reaction is as follows:

Other common insoluble salts which can be prepared by using this method include
calcium sulfate (CaSO 4 ), magnesium carbonate (MgCO 3 ), silver chloride (AgCl),
barium carbonate (BaCO 3 ), barium sulfate (BaSO 4 ), and lead(II) sulfate (PbSO 4 ).

Task 5.6

Use online search tools or other reliable resources to investigate and analyse
various methods used in salt production in Tanzania.

Properties of salts
Salts exhibit different physical and chemical properties.

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