Question

What is the chemical formula of slaked lime?
(A) $ \text{CaO} $
(B) $ \text{CaC}{{\text{O}}_{\text{3}}} $
(C) $ \text{Ca}{{\left( \text{OH} \right)}_{2}} $
(D) $ \text{Ca}{{\left( \text{OH} \right)}_{3}} $

Answer 1

Hint: “Slaked” means “to quench” and lime is a calcium rich inorganic mineral which is primarily composed of oxides and hydroxides, usually calcium oxide or calcium hydroxide.

Complete step by step solution:
Calcium hydroxide is traditionally called “slaked lime” which is an inorganic salt of calcium with the chemical formula $ \text{Ca}{{\left( \text{OH} \right)}_{2}} $ . It is a colourless crystal which when powdered is seen to become white. It is produced when quick lime or calcium oxide ( $ \text{CaO} $ ) is mixed or slaked with water. It has many names including hydrated water, caustic lime, builder’s lime, slack lime, cal, and pickling lime.
Calcium hydroxide finds usage in different applications that includes application in food preparation as well where it is known by the name “E-526”. Limewater is the common name for the saturated aqueous solution of calcium hydroxide. Calcium hydroxide is relatively insoluble in water. At ambient temperatures, calcium hydroxide dissolves in pure water to form an alkaline solution with a pH value of about $ 12.4 $ . Calcium hydroxide solutions can cause chemical burns. At high pH value the solubility decreases drastically this behaviour is relevant to the cement pastes. Calcium hydroxide adopts a polymeric structure that is quite similar to the structure of magnesium hydroxide or brucite.
Hence the correct answer is option C, $ \text{Ca}{{\left( \text{OH} \right)}_{2}} $ .

Note:
Calcium hydroxide is commonly used to prepare lime mortar. It is also used in the preparation of ammonia gas. Another large scale application of calcium hydroxide is its usage in the paper industry where it is an intermediate in the production of sodium hydroxide. It is also widely used in the food industry due to its low toxicity.