Question

The chemical reaction between quicklime and water is characterized by:
A. Evolution of hydrogen gas.
B. Formation of slaked lime precipitate.
C. Change in temperature of mixture
D. Change in colour of the product.

Answer 1

Hint: Try to recall that quick lime is the common name of calcium oxide and when quicklime is added to water then the product formed is used in whitewashing of walls.

Complete step by step solution:
The chemical formula of quick lime is $CaO$ . It is white amorphous solid.
When quicklime is heated in oxyhydrogen flame, it emits a brilliant white light called “limelight”.
When quicklime is added to caustic soda $(NaOH)$ , then it gives a solid which is called “soda-lime”.
It is usually found in the form of hard lumps. When a limited amount of water is added, these lumps break down. During this process, a hissing sound and a large amount of heat is evolved which converts water into steam. This process is called slaking of lime and the fine powder thus obtained is called slaked lime. The reaction which takes place when quicklime is added to water is as follows:
 $CaO + \mathop H\nolimits_2 O \to Ca\mathop {\left( {OH} \right)}\nolimits_2$ .
From the above reaction we can say that, when quick lime is added to water then, formation of slaked lime precipitate takes place.

Hence, we can now conclude that option B is the correct option.

Additional information:
Quicklime is used as flux in metallurgy.
It is also used in the preparation of ammonia and soda-lime.
Quicklime is also used for the preparation of cement, glass, calcium carbide and sodium carbonate.
It is used in building constructions as it is a constituent of mortar.

Note: It should be remembered that quicklime is a basic oxide and hence combines with acids and acidic oxides at high temperature to form corresponding salts. For example:
$CaO + 2HCl \to Ca\mathop {Cl}\nolimits_2 + \mathop H\nolimits_2 O$.