Calcium Oxide (Quick Lime) and Calcium Hydroxide (Slaked lime)

Imagine walking through a construction site and some of the workers can be spotted mixing white powder with water to form a thick adhesive paste. This paste, which hardens into a solid mass, inglazed on walls to make smooth surfaces and seal the finishing for durability. The white powder they are pouring is calcium oxide, otherwise known as quick lime, while the paste is calcium hydroxide, otherwise known as slaked lime. The said compounds prove not only very essential in construction works but also in various industries and common products used every day.

What are Calcium Oxide and Calcium Hydroxide

Quick lime is more commonly known as calcium oxide and is a white, caustic, alkaline, crystalline solid at room temperature. It is prepared by the thermal decomposition of calcium carbonate (limestone) in an otherwise known as calcination—

${Ca CO}_3 (s) \rightarrow {Cao} (s) + {CO}_2 (g)) $

Calcium oxide, also known as quick lime reacts exothermically with water to yield calcium hydroxide, a less caustic but still strongly alkaline material, often called slaked lime:

${CaO} + {H_2O} → {Ca(OH)_2} $

Both are heavily used industrially. Uses of calcium oxide include in cement, steel and paper manufacturing; it is added to water to produce slaked lime, Ca(OH)$_2$, which in turn is sold as a water purification agent, in environments such.

Calcium Oxide(Ca O)
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.

$\begin{aligned} & \mathrm{CaCO}_3 \stackrel{1000^{\circ} \mathrm{C}, \Delta}{\leftrightharpoons} \mathrm{CaO}+\mathrm{CO}_2 \\ & \mathrm{CaO} \xrightarrow{\mathrm{H}_2 \mathrm{O}} \mathrm{Ca}(\mathrm{OH})_2\end{aligned}$

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 heating 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 known as slaking of lime.
• When it is heated with carbon at 3000^oC, calcium carbide is formed. Calcium carbide in reaction with water gives acetylene and 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:

$\mathrm{CaO}+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{Ca}(\mathrm{OH})_2+15 \mathrm{kcal}$

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 the same.

Chemical Properties

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

Uses

• It is used in the softening of water, and purification of coal gas, sugar, etc.
• It is used in the manufacturing of bleaching powder, sodium carbonate, etc.
• It is also used in the making of mortar and plaster used as building materials

Application and Uses of Calcium Compounds

Industrial and Agricultural Applications

Calcium oxide is widely used in cement and mortar processing for buildings. The steel industry cleans its steel, during its refining process, with calcium oxide. Calcium hydroxide is also one of the major components in water therapeutic plants, which has been very effectively applied in treating water to adjust or fine-tune the pH value and clear unwanted particles. Slaked lime is applied to improve the quality of the soil and its acidity, as required by different crops in agriculture processes. It is applied, too, in water, sugar, and pickling processes within the food industry.

Industrial Uses

The importance of calcium oxide and calcium hydroxide does not relate only to the immediate usages that have been explained above. Quick lime finds its use in environmental engineering for the treatment of hazardous waste and flue gas desulfurization, which in return reduces the emission of sulphur dioxide from industrial procedures. Other main usages of calcium hydroxide include tanning in the leather industry and antacids and calcium supplements in the pharmaceuticals.

Recommended topic video on ( Calcium Oxide and Calcium Hydroxide)

Some solved examples

Example 1

Question:

Ca(OH)₂ is known by which name?

1) Lime

2) Quicklime

3) Slaked lime

4) All of these

Solution:

Calcium hydroxide, CaOH₂, is also known as slaked lime.

Answer: 3

Example 2

Question:

Slaking is the process of adding water to turn CaO into which compound?

1) Ca(HCO₃)₂

2) CaCO₃

3) Ca(OH)₂

4) All of these

Solution:

Slaking of lime (CaO) is the process of adding water to form CaOH, which is called slaked lime. The reaction is:

${CaO} + {H}_2{O} \rightarrow {Ca(OH)}_2$

Answer:3

Example 3

Question:

What is the product formed in the reaction: CaO + SiO₂?

1) CaSiO₃

2) CaSiO₄

3) Both 1 and 2

4) None of these

Solution:

Calcium oxide (CaO) reacts with silica (SiO₂) to form calcium silicate (CaSiO₂). The reaction is:

${CaO} + {SiO}_2 \rightarrow{CaSiO}_3 $

Conclusion:

Calcium oxide has different types of applications in the fields of construction, industry, and agriculture. Quick lime is a product of heating the limestone, and slaked lime is a product after the reaction of quick lime with water. The role of such chemicals in a number of technological processes, starting from cement production to treatment of water and improvement of soil quality, is simply irreplaceable. It is their application, practical, and academic perspectives that express their importance in today's world.