What is Quicklime?
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.
$CaC{{O}_{3}}\to CaO+C{{O}_{2}}$
Properties of Quicklime
Physical Properties
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.
Chemical Properties
Calcium oxide reacts readily with water to form calcium hydroxide which is used for many commercial purposes.
$CaO+{{H}_{2}}O\to Ca{{(OH)}_{2}}$
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.
Important Questions
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.
Conclusion
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
Calcium carbonate
Calcium sulphate
Calcium hydroxide
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 ____ ?
Calcium Carbonate
Calcium hydroxide
Plaster of paris
None of the above
Ans: Option 2 - Calcium hydroxide
FAQs on Quicklime
1. Write the application of quicklime in daily life.
Calcium oxide is widely used for white washing. The reaction is shown below.
CaO(s) + H2O(l) → Ca(OH)2(aq) + Heat
A solution of slaked lime produced by above reaction is used for whitewashing walls. Calcium hydroxide reacts slowly with CO2(g) in the air to form a thin layer of CaCO3 on the walls. Calcium carbonate (CaCO3) is formed after some days of whitewashing and gives a shiny finish to the walls. The reaction is shown below.
Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)
2. What is the limelight?
When Calcium oxide is heated to a temperature that is near to its melting point, that is 2400 degrees celsius and 2600 degrees celsius, respectively, it begins to emit a very intense white glow. This type of glow or illumination is referred to as the limelight. Before the discovery of light bulbs, these limelights were widely used. In the 19th century, this feature of calcium oxide was used to provide lighting for the stage. Hence, the limelight is the intense white light that is obtained by heating lime.
3. How is the load carrying capacity of soil increased by the use of calcium oxide?
Quicklime and hydrated lime are said to increase the load carrying capacity of the clay containing soils. The soils that are stabilised with calcium oxide can be used to build embankments, bases, motorway subbases, shape layers on railways, etc. When lime is added to soil, it improves soil geotechnical properties, by reducing plasticity rate and increasing load capacity, and improving its compaction. The three main reasons for this are that quicklime reacts with water in soil and dries the soil, it allows breakage of laminated clay structure, and it stabilises the soil and increases its strength.
