Page 81 - Chemistry ICSE Class X

Study of Acids, Bases and Salts 69
Ammonium hydroxide (NH OH) on heating gives ammonia gas.
4
heat
NH OH(aq) o NH (g) + H O(g)n
2
4
3
ammonium hydroxide ammonia
Solid strong alkalis such as sodium hydroxide (NaOH) and potassium
hydroxide (KOH) melt on heating but do not decompose.
ƒ Reaction with acidic oxides: The oxides of nonmetals (acidic oxides)
react with bases/alkalis to form the corresponding salt and water.
2NaOH(aq) + CO (g) o Na CO (aq) + H O
2
2
3
2
sodium hydroxide carbon dioxide Sodium carbonate water
(alkali) (acidic oxide) (salt)
Ca(OH) (aq) + CO (g) o CaCO (s) + H O(l)
3
2
2
2
calcium hydroxide carbon dioxide calcium carbonate water
ůŬĂůŝƐ ĂďƐŽƌď ĐĂƌďŽŶ ĚŝŽdžŝĚĞ ĨƌŽŵ
2NaOH(aq) + SO (g) o Na SO (aq) + H O(l) ƚŚĞ Ăŝƌ͘
2
2
2
3
sodium hydroxide sulphur dioxide sodium sulphite water
ƒ Reaction with acids: Bases react with acids to form salt and water. The
reaction between an acid and a base is called neutralisation reaction.
NaOH(aq) + HCl(aq) o NaCl(aq) + H O ĂƐĞƐ ŶĞƵƚƌĂůŝƐĞ ĂĐŝĚƐ ƚŽ ĨŽƌŵ ƐĂůƚ
2
sodium hydroxide hydrochloric acid sodium chloride water ĂŶĚ ǁĂƚĞƌ͘
2NaOH(aq) + H SO (aq) o Na SO (aq) + 2H O
4
2
4
2
2
sodium hydroxide sulphuric acid sodium sulphate water
2Al(OH) (s) + 3H SO (aq) o Al (SO ) (aq) + 6H O
4
2
2
2
3
4 3
aluminium hydroxide sulphuric acid aluminium sulphate water
ƒ Reaction with salts of heavy metals. Alkalis like NaOH and the base ůŬĂůŝƐ ƉƌĞĐŝƉŝƚĂƚĞ ŝŶƐŽůƵďůĞ ŵĞƚĂů
NH OH when added to the solutions of salts of heavy metals, such as ŚLJĚƌŽdžŝĚĞƐ ĨƌŽŵ ƚŚĞŝƌ ƐĂůƚ ƐŽůƵƟŽŶƐ͘
4
copper, iron, zinc, lead, etc. insoluble metal hydroxide precipitated
out.
CuSO (aq) + 2NH OH(aq) o Cu(OH) (s)p + (NH ) SO (aq)
4
2
4
4 2
4
copper sulphate (dropwise)
limited amount
ZnSO (aq) + 2NaOH(aq) o Zn(OH) (s)p + Na SO (aq)
2
4
4
2
zinc sulphate (dropwise)
limited amount
FeSO (aq) + 2NaOH o Fe(OH) (s)p + Na SO (aq)
2
4
4
2
ferrous sulphate (dropwise)
limited amount
Uses of Bases
What are the uses of some common bases
The uses of some typical common bases are described below:
ƒ Sodium hydroxide Š In soap and detergent industry
(caustic soda) (NaOH) Š For the manufacture of rayon ^ŽĂƉ ŝƐ ƉƌĞƉĂƌĞĚ ďLJ ŚĞĂƟŶŐ ŽŝůͬĨĂƚ
Š In paper and pulp industry ǁŝƚŚ ĐĂƵƐƟĐ ƐŽĚĂ ;ƐŽĚŝƵŵ ŚLJĚƌŽdžŝĚĞͿ͘
Š For manufacturing other chemicals Kŝů ;Žƌ ĨĂƚͿ н EĂK,;aqͿ
'
ƒ Calcium hydroxide Š For white washing o ^ŽĂƉ н 'ůLJĐĞƌŽů
(slakedlime) [Ca(OH) ] Š For the manufacture of bleaching ͻ
2
powder ĂůĐŝƵŵ ŚLJĚƌŽdžŝĚĞ ŝƐ ŽŶůLJ ƐůŝŐŚƚůLJ
Š In leather industry ƐŽůƵďůĞ ŝŶ ǁĂƚĞƌ͘ ^ŽůƵƟŽŶ ŽĨ
ĐĂůĐŝƵŵ ŚLJĚƌŽdžŝĚĞ ŝŶ ǁĂƚĞƌ ŝƐ ĐĂůůĞĚ
Š For neutralising acidity of the soil limewater͘
Š For softening hard water
Š As an insect/pest killer