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The S-Block Elements

Question
CBSEENCH11007160
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How is slaked lime prepared? What are its properties and uses?

Solution

Slaked lime is prepared by the following methods:
(i) From quick lime: By treating quicklime with water, slaked lime is formed. 
    CaO space plus space straight H subscript 2 straight O space rightwards arrow space space Ca left parenthesis OH right parenthesis subscript 2 space plus space Heat
When water is added to quicklime, a huge amount of heat is produced along with the hissing sound. 
(ii) From calcium chloride: By treating calcium chloride with caustic soda, slaked lime is formed.
CaCl subscript 2 space plus space 2 NaOH space rightwards arrow space space Ca left parenthesis OH right parenthesis subscript 2 space plus space 2 NaCl
Properties:
(i) Slaked lime is a white amorphous powder.
(ii) A suspension of slaked lime in water is called milk of lime.
(iii) The aqueous layer which is decanted from the precipitated calcium hydroxide is called lime water.
(iv) On passing carbon dioxide through lime water, the lime water turns milky due  to the formation of insoluble calcium carbonate. 
Ca left parenthesis OH right parenthesis subscript 2 left parenthesis aq right parenthesis space plus space CO subscript 2 left parenthesis straight g right parenthesis space rightwards arrow space space CaCO subscript 3 left parenthesis straight s right parenthesis space plus space straight H subscript 2 straight O left parenthesis straight l right parenthesis
If carbon dioxide is passed in excess, a clear solution is again obtained. This is because the insoluble calcium carbonate changes into soluble calcium bicarbonate.
stack CaCO subscript 3 left parenthesis straight s right parenthesis with Insoluble below space plus space straight H subscript 2 straight O left parenthesis straight l right parenthesis space plus space CO subscript 2 left parenthesis straight g right parenthesis space rightwards arrow space space space stack Ca left parenthesis HCO subscript 3 right parenthesis subscript 2 with Soluble below left parenthesis aq right parenthesis
If the clear solution is heated, it again turns milky due to the decomposition of calcium bicarbonate into calcium carbonate. 
stack Ca left parenthesis HCO subscript 3 right parenthesis subscript 2 with left parenthesis Soluble right parenthesis below space rightwards arrow with Heat on top space CaCO subscript 3 left parenthesis straight s right parenthesis space plus space CO subscript 2 left parenthesis straight g right parenthesis space plus space straight H subscript 2 straight O left parenthesis straight l right parenthesis
(v) Slaked lime reacts with chlorine to form bleaching powder.
 
Ca left parenthesis OH right parenthesis subscript 2 left parenthesis straight s right parenthesis space plus space Cl subscript 2 left parenthesis straight s right parenthesis space rightwards arrow stack CaOCl subscript 2 left parenthesis straight s right parenthesis with Bleaching space powder below

Uses. It is used:
(i) for the preparation of ammonia
(ii) for white washing
(iii) in the purification of sugar
(iv) in the softening of hard water.

Some More Questions From The s-Block Elements Chapter

What are s-block elements?

Why are alkali metals not found in nature?

Lithium shows similarities to magnesium in the chemical behaviour. What is the cause of this similarity?

What is the nature of lithium compounds?

Group 1 elements are called alkali metals. Why?

Why caesium can be used in photoelectric cell while lithium can not be?

In aqueous solution, Li+ ion has lowest mobility. Why?

Lithium has highest ionisation energy in group 1 elements, yet it is strongest reducing agent. Comment.

The softness of group 1 elements increases down the group with increasing atomic number. Give reason. 

Which is the most reactive alkali metal and why?

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