2. Those reactions in which elements takesthe place of another
elements ina compound are known asdisplacement reactions.
Generally a more reactive element displaces a less reactive
element.
WHAT ARE
DISPLACEMENT
REACTIONS?
4. Single displacement reactions
A single displacement reaction is one in which a single element replaces
another element which is in a compound.
EXAMPLE:
Mg(s) + 2HCl(aq) → H2(g) + MgCl2(aq)
In the above reaction, magnesium metal diaplaces hydrogen from its chloride
to form magnesium chloride and hydrogen gas. Here, magnesium is more
reactive than hydrogen.
5. EXAMPLE...
• When a strip of zinc metal is placed in copper sulphate solution, then zinc sulphate and copper
are formed.
CuSO4(aq.) + Zn(s) → ZnSO4(aq.) +Cu(s)
Copper Sulphate Zinc Zinc Sulphate Copper
(Blue solution) (Colourless solution)
In this reaction zinc displaces copper from copper sulphate
compound so that copper is free. This displacement reaction takes place because
zinc is more reactive than copper.
6. EXAMPLE...
• When a piece of iron metal is placed in copper sulphate solution, then iron sulphate solution and copper
metal are formed.
CuSO4(aq.) + Fe(s) → FeSO4(aq.) + Cu(s)
Copper Sulphate Iron Zinc Sulphate Copper
(Blue solution) (Greenish solution)
In this reaction, iron displaces copper from copper sulphate solution.
The deep blue colour of copper sulphate solution fades due to the
formation of green solution of iron sulphate. A red brown coating (or layer) of copper metal is
formed on the surface of iron metal (or iron nail).
9. DOUBLE DISPLACEMENTREACTIONS
A double-replacement reaction is a reaction in which the positive and negative ions of two ionic
compounds exchange places to form two new compounds. The general form of a double-
displacement reaction is:
AB+CD→AD+BC
EXAMPLE:
AgNO3 + NaCl → AgCl + NaNO3
The reaction between silver nitrate and sodium chloride is a double displacement reaction. The
silver trades its nitrite ion for the sodium's chloride ion, causing the sodium to pick up the nitrate
anion.
10. EXAMPLE...
• BaCl2(aq.) + Na2SO4(aq.) → BaSO4(s) + NaCl(aq.)
Barium Chloride Sodium Sulphate Barium Sulphate Sodium Chloride
(white precipitate)
In the above reaction, barium chloride solution is added to
sodium sulphate solution and a white precipitate of barium sulphate
is formed along with sodium chloride solution.
* Any reaction in which an insoluble solid called precipitate is formed that separates from
the solution is called Precipitation reaction.
11. AgNO3 + NaCl → AgCl (s) + NaNO3
Pb(NO3)2 + 2KI → PbI2 (s) + 2KNO3
BaCl2 + Na2SO4 → BaSO4 (s) + 2NaCl
Al2(SO4)3 + 6NH4OH → 2Al(OH)3 (s) + 3(NH4)2SO4
2KBr+BaI2→ 2KI+BaBr2
HBr+KOH → KBr+H²O
SomeMore Examples
