Page 132 - ICSE Chemistry 8

• Fe(s) + CuSO (aq) FeSO (aq) + Cu(s)
4
4
Iron Copper(II) sulphate Iron(II) sulphate Copper
(grey) (blue) (pale green) (reddish-brown)

Double Displacement Reaction
Thirst for Knowledge
A chemical reac on in which two compounds react by
exchange of ions to form two new compounds is called a The forma on of a precipitate is shown
double displacement reac on. The general representa on by an arrow poin ng downwards (↓)
of such a reac on is as shown. and that of gas is shown by an arrow
poin ng upwards (↑).
AB + CD AD + BC

Double displacement reac on are of two types: precipita on reac on and neutralisa on reac on.

Precipitation Reaction

A chemical reac on in which an insoluble solid called precipitate separates from the solu on is called a
precipita on reac on.

Examples:

• Reac on of barium chloride and copper sulphate: Barium chloride and copper sulphate in the
form of a solu on react to form a white precipitate of barium sulphate.

BaCl (aq) + CuSO (aq) BaSO (s)  + CuCl (aq)
2
2
4
4
Barium chloride Copper sulphate Barium sulphate Copper chloride
(white ppt)
• Reac on of sodium chloride and silver nitrate: Sodium chloride and silver nitrate in the form of a
solu on react to form a white precipitate of silver chloride.

NaCl(aq) + AgNO (aq) AgCl(s)  + NaNO (aq)
3
3
Sodium chloride Silver nitrate Silver chloride Sodium nitrate
(white ppt)
Some more examples of precipita on reac ons are listed below.

• Pb(NO ) (aq) + 2Kl(aq) PbI (s) + 2KNO (aq)
3 2
3
2
Lead nitrate Potassium iodide Lead iodide Potassium nitrate
(golden yellow ppt)
• Na CO (aq) + Pb(NO ) (aq) PbCO (s)  + 2NaNO (aq)
3
3
3
2
3 2
Sodium carbonate Lead nitrate Lead carbonate Sodium nitrate
Neutralisation Reaction
A chemical reac on in which an acid reacts with a base to form salt and water is called a neutralisa on
reac on.

Acid + Base Salt + Water

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