Question

Which of the following is a correct observation when water is added to quick lime?
A.Vigorous bubbling and Hissing sound. Both
B.Slow bubbling with no sound
C.Vigorous bubbling with the evolution of heat hissing sound
D.No change

Answer 1

Hint:Quick lime is known as calcium oxide ($CaO$). It is a white caustic alkaline and is obtained by heating limestone.Quicklime is produced by heating crushed limestone to around 1,100 degrees Celsius in a shaft furnace or rotary kiln.

Complete step by step answer:
The calcium oxide i.e. quick lime is usually obtained in the form of hard lumps. The addition of a limited amount of water breaks these lumps. During the process, a hissing sound and a large amount of heat are evolved which converts water into steam. This process is known as slaking of lime and the fine powder is obtained as a product is slaked lime, also known as calcium hydroxide. The chemical formula for calcium hydroxide is $Ca{(OH)_2}$.
The chemical reaction involved during the process of slaking of lime is given below:
$CaO + {H_2}O \to Ca{(OH)_2}$
The enthalpy change during the reaction is -64.5KJ/mol.
Here the negative (–) sign shows the release of energy hence we can say it is exothermic energy.

Hence the correct answer is option C.

Additional information- If we add an excess of calcium hydroxide in water, a saturated solution of calcium hydroxide is formed which is known as lime water and the suspension of slaked lime in water is called milk of lime. The nature of lime water is basic and therefore the PH value for lime water is above 7.


Note:
If we talk about the uses of slaked lime produced by the reaction of quick lime with water, then we can say it is used as a building material in the form of mortar. It is also used in the manufacture of bleaching powder.