The s-Block Elements

Question 189
CBSEENCH11007167

Give one method of preparing quick lime. What happens when rain water falls on it?

Solution

Calcium oxide is called quicklime. It is prepared by heating the lime stone in a rotatory kiln at 1070-1270 K.
CaCO subscript 3 space rightwards harpoon over leftwards harpoon with 1070 minus 1270 space straight K on top space CaO space plus space CO subscript 2 upwards arrow
CO2 formed escapes and hence the above equilibrium shifts towards the formation of calcium oxide. 
When rain-water falls on quick lime, slaked lime is formed.
CaO space plus space straight H subscript 2 straight O space rightwards arrow space space space stack Ca left parenthesis OH right parenthesis subscript 2 with Slaked space lime below

Question 190
CBSEENCH11007168

Name a few important uses of quick lime. 

Solution

It is used:
(i) in the preparation of cement, glass and calcium carbide. 
(ii) in the purification of sugar
(iii) in drying alcohol and non-acidic gases like ammonia etc.,
(iv) in softening of hard water. 
(v) as a flux in the extraction of metals. 
(vi) in agriculture as a fertiliser, disinfectant and germicide.

Question 191
CBSEENCH11007169

Starting with CaCO3, write balanced chemical equation showing the preparation of:
(i) CaO        (ii) CaSO4        (iii) Ca(OH)2       (iv) Ca(HCO3)2 solution.

Solution
left parenthesis straight i right parenthesis space CaCO subscript 3 space rightwards arrow with Heat on top space CaO space plus space CO subscript 2
left parenthesis ii right parenthesis space CaCO subscript 3 space plus space straight H subscript 2 SO subscript 4 left parenthesis dil. right parenthesis space rightwards arrow with Heat on top space CaSO subscript 4 space plus space CO subscript 2 space plus space straight H subscript 2 straight O
left parenthesis iii right parenthesis space CaCO subscript 3 space rightwards arrow with Heat on top space CaO space plus space CO subscript 2
CaO space plus space straight H subscript 2 straight O space space rightwards arrow space space space space Ca left parenthesis OH right parenthesis subscript 2
left parenthesis iv right parenthesis space CaCO subscript 3 space plus space CO subscript 2 space plus space straight H subscript 2 straight O space rightwards arrow space space Ca left parenthesis HCO subscript 3 right parenthesis subscript 2
Question 192
CBSEENCH11007170

Describe two important uses of the following;
(a) Caustic soda (b) Sodium carbonate   (iii) Quick lime.

Solution

(i) Caustic soda
It is used:
(a) in the manufacture of sodium metal, soap (from oils and fats), rayon, paper, dyes and drugs,
(b) for mercerising cotton to make cloth unshrinkable.

(ii) Sodium carbonate
It is used:
(a) in laundries and in softening of water as washing soda,
(b) in the manufacture of glass, caustic soda, soap powders etc.
(iii) Quick lime
It is used:
(a) in the purification of sugar and in the manufacture of dyestuffs,
(b) in the manufacture of bleaching powder, slaked lime and lime colours.

 

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