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Calcium Oxide (Quick Lime) and Calcium Hydroxide (Slaked lime) - Practice Questions & MCQ

Edited By admin | Updated on Sep 18, 2023 18:35 AM | #JEE Main

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14 Questions around this concept.

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Compound A reacts with NH₄Cl and forms a compound B. Compound B reacts with H₂O and excess of CO₂ to form compound C which on passing through or reaction with saturated NaCl solution forms sodium hydrogen carbonate.
Compound A, B and C, are respectively.

$\mathrm{CaCl}_2, \mathrm{NH}_3, \mathrm{NH}_4 \mathrm{HCO}_3$

$\mathrm{Ca}(\mathrm{OH})_2, \mathrm{NH}_4^{\oplus},\left(\mathrm{NH}_4\right)_2 \mathrm{CO}_3$

$\mathrm{CaCl}_2, \mathrm{NH}_4^{\oplus},\left(\mathrm{NH}_4\right)_2 \mathrm{CO}_3$

$\mathrm{Ca}(\mathrm{OH})_2, \mathrm{NH}_3, \mathrm{NH}_4 \mathrm{HCO}_3$

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$\mathrm{CaH}_2$ is hydrolysed by water to give a basic solid A and a flammable gas B. What is A and B?

$\text { A: } \mathrm{CaO} \text { B: } \mathrm{O}_2$

$\mathrm{A}: \mathrm{CaCO}_3 \quad \mathrm{~B}: \mathrm{O}_2$

$\mathrm{A}: \mathrm{Ca}(\mathrm{OH})_2 \quad \mathrm{~B}: \mathrm{H}_2$

$\text { A: } \mathrm{CaO} \mathrm{B}: \mathrm{H}_2$

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Concepts Covered - 0

Calcium Oxide (Quick Lime) - CaO and Calcium Hydroxide (Slaked lime) - Ca(OH)2

Calcium Oxide(CaO)
It is called burnt lime or lime also.

Preparation
It is prepared by heating limestone in a rotary kiln at 800-1000^oC. Since it is a reversible reaction the evolved CO₂ must be removed so that the equilibrium may shift in the forward direction.

$\\\mathrm{CaCO}_{3}\: \overset{\mathrm{1000^{o}C,\: \Delta }}\leftrightharpoons\mathrm{CaO} + CO_2\: \\\\\mathrm{CaO}\overset{\mathrm{H_{2}O}}\longrightarrow\: \mathrm{Ca(OH)_{2}}$

slaked lime

Physical Properties

It is a white amorphous solid with a melting point of 287K.
On exposure to the atmosphere, it absorbs moisture and CO₂.
On hearing in an oxyhydrogen flame, it becomes incandescent and releases a bright white light called limelight.

Chemical Properties

Being a basic oxide it reacts with acidic oxides to form salts as follows:
On reaction with water, it forms calcium hydroxide with a hissing sound. II is an exothermic reaction and known as slaking of lime.
When it is heated with carbon at 3000^oC, calcium carbide is formed. Calcium carbide on reaction with water gives acetylene and with nitrogen gives CaCN₂.

Uses

It is used in the manufacture of glass, cement, bleaching powder, soda-lime etc.
It is used as a basic flux.
It is used as a drying agent for gases and alcohols.
It is used in the refining of sugar.
It is also used as a disinfectant and germicide.
It is used for whitewashing.

Calcium Hydroxide(CaOH)₂
It is also known as slaked lime

Preparation
It is prepared by the reaction of lime with water as follows:
$\mathrm{CaO}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{Ca}(\mathrm{O} \mathrm{H})_{2}+15 \mathrm{k} \mathrm{cal}$

Physical Properties

It is a white amorphous powder and sparingly soluble in water. Its suspension in water is called milk of lime while the clear solution is called lime water but chemically both are same.

Chemical Properties

Its slowly absorbs CO₂ from air forming insoluble milky solution of calcium carbonate. If more CO₂ is passed in this milky solution, soluble calcium bicarbonate is formed and milkiness gets disappeared.
When it is reacted with chlorine in cold milk of lime form, calcium hypochlorite is formed bur when it is hot, calcium chlorate is formed.

Uses