Page 93 - Chemistry ICSE Class X

Study of Acids, Bases and Salts 79

By direct combination of elements
Water-soluble salts, such as sodium chloride (NaCl) and ferric chloride
(FeCl ), can be obtained by direct combination of the elements.
3
ƒ NaCl can be obtained by passing Cl gas over heated sodium
2
heated
2Na(s) + Cl (g) o 2NaCl(s)
2
sodium chlorine
ƒ Ferric chloride (FeCl ) can be obtained by passing chlorine over heated
3
KTQP ſNKPIU
2Fe(s) + 2Cl (g) o 2FeCl (s)
2
3
KTQP ſNKPIU JGCVGF HGTTKE EJNQTKFG
By simple displacement method (or by the reaction of a metal with
an acid)
Active metals displace hydrogen from dilute acids, and corresponding salt
is formed. This method is generally used for preparing soluble chlorides
and sulphates.
For example, zinc, magnesium and iron react with dilute acids to form
corresponding salt and hydrogen is liberated.
Zn(s) + H SO (dil.) o ZnSO (aq) + H (g)
4
2
4
2
zinc sulphuric acid zinc sulphate hydrogen
Zn(s) + 2HCl(dil.) o ZnCl (aq) + H (g)
2
2
zinc hydrochloric acid zinc chloride hydrogen
Mg(s) + H SO (dil.) o MgSO (aq) + H (g)
2
4
4
2
magnesium sulphuric acid magnesium sulphate hydrogen
heat
Fe(s) + H SO (dil.) o FeSO (aq) + H (g)
2
4
2
4
KTQP ſNKPIU UWNRJWTKE CEKF HGTTQWU UWNRJCVG J[FTQIGP
By decomposing the salts of more volatile acids with less volatile
acids
This method is used for preparing soluble nitrates, chlorides, sulphates
from salts like bicarbonates, carbonates, sulphites, bisulphites, chlorides
and nitrates. For example,
ƒ Decomposition of carbonates and hydrogencarbonates with dilute
acids forming the corresponding salt and liberating carbon dioxide
Na CO (aq) + 2HCl(aq) o 2NaCl(aq) + CO (g) + H O
2
2
3
2
sodium carbonate hydrochloric acid sodium chloride carbon dioxide water
ZnCO (aq) + H SO (dil.) o ZnSO (aq) + CO (g) + H O
2
2
3
2
4
4
zinc carbonate zinc sulphate carbon dioxide water
CuCO (s) + H SO (dil.) o CuSO (aq) + CO (g) + H O
3
4
2
2
2
4
copper carbonate copper sulphate water
NaHCO (aq) + HCl(dil.) o NaCl(aq) + CO (g) + H O
3
2
2
sodium bicarbonate sodium chloride water
ƒ Decomposition of chlorides with conc. sulphuric acid
', < 200°C
NaCl(s) + H SO (l) o NaHSO (aq) + HCl(g)
2
4
4
sodium chloride sulphuric acid sodium hydrogen hydrogen chloride
(conc.) sulphate (acid salt)
', > 200°C
2NaCl(s) + H SO (l) o Na SO (aq) + 2HCl(g)
4
2
4
2
sodium chloride conc. sodium sulphate hydrogen chloride
sulphuric acid (normal salt)