Page 51 - Chemistry ICSE Class IX
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Chemical Changes and Reactions 39
CuSO (aq) + Zn(s) o Cu(s) + ZnSO (aq)
4
4
copper sulphate (blue) zinc copper metal zinc sulphate
(colourless)
CuSO (aq) + Mg(s) o Cu(s) + MgSO (aq)
4
4
copper sulphate (blue) magnesium copper metal magnesium sulphate
(colourless)
Metals, such as iron, zinc and magnesium, are more reactive (more
electropositive) than copper.
Displacement of less active halogen from the solution of
corresponding halide by a more active halogen is also a
displacement reaction. For example, chlorine displaces bromine
and iodine from bromides and iodides:
2KBr(aq) + Cl (aq) o 2KCl(aq) + Br (aq)
2
2
potassium bromide chlorine potassium chloride bromine ŚůŽƌŝŶĞ ŝƐ ŵŽƌĞ ĞůĞĐƚƌŽŶĞŐĂƟǀĞ
(colourless) (deep yellow) ƚŚĂŶ ďƌŽŵŝŶĞ ĂŶĚ ŝŽĚŝŶĞ͘
2KI(aq) + Cl (aq) o 2KCl(aq) + I (aq)
2
2
potassium iodide chlorine potassium chloride iodine
(colourless) (deep brown)
Displacement of hydrogen from acids by active metals is also a
displacement reaction. For example, zinc metal displaces hydrogen
from dilute hydrochloric and dilute sulphuric acids.
Zn(s) + 2HCl(dil.) o ZnCl (aq) + H (g)
2
2
zinc hydrochloric acid zinc chloride hydrogen
Zn(s) + H SO (dil.) o ZnSO (aq) + H (g)
4
2
4
2
zinc sulphuric acid zinc sulphate hydrogen Copper is less reactive than iron,
zinc, magnesium
What is a double displacement reaction
A reaction in which the two reacting ionic compounds exchange their
corresponding ions is called a double displacement reaction. Typical
double displacement reactions are,
Reaction between silver nitrate and sodium chloride in solution.
AgNO (aq) + NaCl(aq) o NaNO (aq) + AgCl(s)p
3
3
silver nitrate sodium chloride sodium nitrate silver chloride
(white precipitate)
Reaction between BaCl and H SO in solution.
4
2
2
BaCl (aq) + H SO (aq) o 2HCl(aq) + BaSO (s)p
4
4
2
2
barium chloride sulphuric acid hydrochloric acid barium sulphate
(white precipitate)
Potassium bromide and
What is a precipitation reaction
potassium iodide reacting with
The reaction in which one of the products formed is an insoluble substance chlorine
and is thrown out of the solution as solid (called precipitate) is called
precipitation reaction. The substance that separates out as precipitate is
indicated by a downward arrow (p).
Some precipitation reactions are:
Reaction between silver nitrate and sodium chloride A н C o A н C
AgNO (aq) + NaCl(aq) o AgCl(s)p + NaNO (aq) ŽƵďůĞ ĚŝƐƉůĂĐĞŵĞŶƚ ƌĞĂĐƟŽŶ
3
3
silver nitrate sodium chloride silver chloride sodium nitrate
(white precipitate)
Reaction between barium chloride and sulphuric acid
BaCl (aq) + H SO (aq) o BaSO (s)p + 2HCl(aq)
2
4
2
4
barium chloride sulphuric acid barium sulphate hydrochloric acid
(white precipitate)
