Compounds of Calcium

1.      Calcium oxide (Quick Lime)

• Lime stone found in nature is the starting material of almost all the compounds of calcium.
• Calcium oxide is also called Quick line.
• The decomposition of calcium carbonate is a reversible process 
  

  CaCO₃ ⇋ CaO + CO₂

  
• When water is added to lime, a hissing sound is produced along with clouds of steam. In this process a large amount of heat energy is given out.
  

  CaO + H₂O   → Ca(OH)₂     + Heat
  

  Quick lime                        Slaked Lime      Energy

Uses of Quick lime:

1. As it has high melting point (260⁰C) it is used for furnace lining.
2. It is used as a basic flux in metallurgy as it combines with acidic impurities.
   

   CaO + SiO₂ → CaSiO₃
3. It is used as disinfectant and germicide, as a drying agent for ammonia and alcohol.
4. It is employed for the purification of coal gas and softening of water.

2.      Lime water: [Ca (OH)₂] [Calcium Hydroxide]

• The chemical formula is Ca(OH)₂
• When water is added to lime, a hissing sound is produced along with clouds of steam in this process a large amount of heat energy is given out. The lime cracks with the formation of a powder called slacked lime Ca (OH)₂.
  

  CaO + H₂O   → Ca(OH)₂     + Heat

  
  

  Quick lime                        Slaked Lime      Energy
• The above process is known as slaking of lime
  

Uses of slacked lime: [Ca (OH)₂]

1. Slaked lime is applied to acidic soils to regulate the soil’s pH levels.
2. This allows for faster growth of crops by aiding the intake of nutrients and nitrogen by vegetation growing in the soil.
3. Calcium hydroxide is also used as a filler material in rubber and plastics, serving as an acceleration in the rubber.

3.      Calcium carbonate: [CaCO₃]

• It is found in nature in huge quantities in various forms such as lime stone, marble, chalk.
• It can be obtained by passing carbon dioxide through lime water (or) by adding sodium carbonate solution to CaCl₂
  

  Ca (OH)₂ + CO₂ → CaCO₃ + H₂O

  CaCl₂ + Na₂CO₃ → CaCO₃ ↓ + 2NaCl
• The precipitate of CaCO₃ thus obtained is known as precipitated chalk.
  
• It is a white powder, insoluble in water. It dissolves in presence of CO₂ due to formation of calcium bicarbonate.
  

  CaCO₂ + H₂O + CO₂ →Ca (HCO₃)₂

Uses of CaCO₃

1. Precipitated chalk is used in tooth pastes and face powders, in medicine for indigestion, in adhesives and in cosmetics.
2. Chalk is used in paints and distempers.
3. Marble is used in for building purposes, production of CO₂ in laboratory.
4. Lime stone is used:
1. In the manufacture of the quick lime, slacked lime, cement, washing soda and glass.
2. Used as flux in the smelting of iron and lead ores.

4.      Plaster of Pairs: [2CaSO₄ H₂O] [Calcium sulphate dihydrate]

Preparation:

It is obtained when gypsum, calcium sulphate dihydrate [2CaSO₄ 2H₂O] is heated at 120⁰C

2[CaSO₄ 2H₂O] → 2CaSO₄ H₂O + 3H₂O

                   Plaster of Paris

Properties:

• Plaster of Paris is a white powder
• It has the property of setting to a hard mass when a paste with water is allowed to stand aside for some time. Slight expansion occurs during the setting as water is absorbed to reform CaSO₄ 2H₂O (gypsum)
• The setting takes place in two stages:
• In the first stage, there is conversion of Paris into orthorhombic form of gypsum and in the second stage orthorhombic form changes into monoclinic form.
  

  

Uses:

1. It is used in surgery for setting broken (or) dislocated bones.
2. In making casts for statue, toys, surgical instruments etc…
3. In making casts in dentistry.
4. In making black board chalk

5.      Portland cement:

• Cement is one of the most important building materials at the present time. It is used in the construction of buildings, roads, bridges, dams.
• Cement is a dirty greenish heavy powder containing calcium aluminates and silicates.

Composition of Portland cement:

Calcium Oxide	(CaO)	61.5%
Silica	(SiO₂)	22.5%
Alumina	(Al₂O₃)	7.5%
Magnesium Oxide	(MgO)	2.5%
Ferric Oxide	(Fe₂O₃)	2.0%
Potassium Oxide	(K₂O₃)	1.5%
Sulphur Oxide	(SO₃)	1.0%

Raw Material:

The important Raw materials needed for the manufactures of cement are

1. Lime stone – The provides lime
2. Clay – This provides alumina and silica
3. Gypsum

Manufacture of Cement:

1. Dry Process
2. Wet Process

Dry Process:

• The process is used when lime stone is hard in nature.
• The lime stone is first broken into small pieces.
• It is then mixed with clay in proper proportions.
• The mixture is finally pulverized to such an extent that it possess through a 100 mesh sieve.
• This homogeneous mixture is known as raw material.

Wet Process:

• The process is used when lime stone and clay both are soft in nature.
• The clay is washed with water in wash mill to remove foreign materials like flint.
• The powdered lime stone is mixed with clay paste in the ratio of 75% (Lime Stone) and 25% (Clay).
• The mixture is finely ground and made homogeneous paste is known as surely. It contains 40% of water.