Burnt lime or Quicklime is an alternate name for the chemical compound calcium oxide. Calcium oxide is represented by the chemical formula CaO. It exists as a white crystalline solid at standard conditions for temperature and pressure. It is inexpensive and abundant. Also, quicklime is caustic and alkaline at standard conditions. Quicklime and its derivatives like calcium hydroxide or slaked lime are very important chemical commodities.
How to Prepare Quicklime?
Quicklime can be easily prepared from the decomposition of limestones or sea shells that are readily available. Since limestones and sea shells contain calcium carbonate, they can be processed to produce burnt lime through the process of calcination. In calcination, reactants are thermally decomposed at high temperatures which are below the melting point of the reactants.
During the process of calcination, the byproducts are carbon dioxide and burnt lime.
Properties of Quicklime
It is a shapeless white amorphous powder with high melting and boiling points, which are 2,572oC or 4,662oF and 2,850oC or 5162oF, respectively. The molecular weight of quicklime is 56.08 gram per mole. It is a highly insoluble and thermally stable compound, therefore it is suitable for glass and ceramic applications. It does not conduct electricity. It is insoluble in alcohol and hard to decompose since it is very stable.
Calcium oxide reacts readily with water to form calcium hydroxide which is used for many commercial purposes.
Uses and Applications of Quicklime
Quick lime is used in the manufacture of iron and steel, and paper and pulp.
A combination of phenolphthalein and calcium oxide is used in water detection pastes.
Used in making porcelain and glass.
In preparation of bleaching powder, calcium carbide, and calcium cyanamide.
In water softeners.
Also in mortars and cement.
In agriculture, it is also used for treating acidic soils. This process is called liming.
Due to its incandescence when heated, it is used in Drummond lights or limelights also.
1. What are the possible health hazards that calcium oxide can cause?
Ans: Quick lime can cause irritation to the eyes and skin; therefore, full personal protective equipment should be worn before handling this compound. If quicklime comes in contact with the eyes, it is advised to thoroughly wash the eyes and contact the doctor immediately. If quicklime dust is inhaled, there is a possibility of irritation in the respiratory tract.
2. What is the difference between Quicklime and Hydrated lime?
Ans: Hydrated lime is formed when water is added to powdered quicklime and the resulting mixture is placed in a kiln or an oven and ten pulverised with water. Meanwhile, Calcium Oxide is formed from the thermal decomposition of calcium carbonate. Calcium oxide is said to be more reactive than hydrated lime because of its higher density.
3. How do you define the term calcination?
Ans: Calcination is the preparation process of burnt lime where reactants are thermally decomposed at high temperatures. But it is ensured that the temperatures are less than their respective melting points.
Calcium oxide or quicklime is prepared from the decomposition of calcium carbonate or limestone which is available from natural resources like limestones, fossils, or seashells. It is white amorphous solid, and a highly stable compound with a melting point of around 2600oC. Above 2400 degrees celsius, it emits an intense glow. Its appearance varies from white to pale yellow or brown under standard conditions. It is used for many commercial purposes. It is used for manufacturing steel, iron, paper, pulp, basic oxygen steelmaking process, etc.
Practise Multiple Choice Questions
1. What are/is the reactant/s for the preparation of calcium oxide?
Calcium and oxygen
Ans: Option B - Calcium carbonate
2. Which among the following describes calcium oxide best?
Bluish, odourless alkaline substance
Whitish, sweet smelling acidic substance
Whitish, odourless alkaline substance
Greyish, sweet smelling acidic substance
Ans: Option C - Whitish, odourless alkaline substance
3. Calcium oxide reacts vigorously with water to form ____ ?
Plaster of paris
None of the above
Ans: Option 2 - Calcium hydroxide