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Quick Lime Calcium Oxide & Calcium Hydroxide

Calcium Oxide

What is Calcium Oxide (CaO)?

Calcium Oxide, known as lime, is a chemical compound with the formula CaO.

Calcium oxide, also known as quicklime, is an alkaline substance that has been in use since the medieval age. It is believed that quicklime is one of the oldest chemicals known to the human race. It can also be referred to as burnt lime or lime.

Calcium oxide has a medium viscosity and a high surface tension, plus a high to intermediate expansion and contraction rate. This material isn’t volatile at ceramic temperatures. Calcium oxide has a moderate effect on color, except in large amounts when it may have a bleaching effect on iron oxide. It also exists in the color of kaki/tomato reds.

Preparation of Calcium Oxide

Calcium oxide can be produced by the thermal decomposition of materials like limestone or seashells that contain calcium carbonate (CaCO3; mineral calcite) in a lime kiln. The process that is used to prepare burnt lime is known as calcination. It is a process that starts with thermally decomposing the reactants at high temperatures but ensuring that the temperature is kept well below the melting point.

Calcium carbonate undergoes calcination at temperatures ranging between 1070 Co-1270Co. These reactions are usually held in a rotary kiln. The products formed as a result of the reaction are burnt lime and carbon dioxide. The carbon dioxide that is formed is immediately removed so that the reaction is preceded until the completion of the process in accordance with Le-Chatelier’s principle. This reaction is reversible and exothermic in nature in the forward direction.

CaCO3 → CaO + CO2

Properties of Calcium Oxide

  • Calcium Oxide is an amorphous white solid with a high melting point of 2600c
  • It is a very stable compound and withstands high temperatures.
  • In the presence of water, it forms slaked lime. This process is called the slaking of lime. CaO+H2O → Ca (OH)2.
  • It is an oxide that is basic in nature and forms salts when it comes in contact with an acid.
  • This compound crystallizes in a cubic crystal lattice.
  • The standard molar entropy associated with calcium oxide corresponds to 40 joules per mole kelvin.
  • This compound is known to emit an intense glow when it is heated to temperatures above 2400co degrees Celsius.
Calcium Oxide

Uses of Calcium Oxide

  • It is extensively used for medicinal purposes and insecticides.
  • in the manufacturing of cement, paper, and high-grade steel.
  • Lime is used as a reagent in laboratories for dehydration, precipitation reaction, etc.
  • It is the cheapest alkali available which is an important ingredient in the manufacturing of caustic soda.
  • Calcium is essential to animal life as the constituent of bones, shells, and teeth. The most common of the calcium compounds is calcium carbonate which the potter uses as a source of calcium oxide for glazes.

Calcium Hydroxide

What is Calcium Hydroxide?

Calcium hydroxide, commonly referred to as slaked lime, is described by the chemical formula Ca (OH)2. It is an inorganic compound that has a white, powdery appearance in its solid state. However, Ca (OH)2 has a colorless appearance in its crystalline form.

The alternate names of this compound include hydrated lime, slack lime, pickling lime, and caustic lime. Generally, calcium hydroxide is prepared by mixing water and calcium oxide (also known as quick lime).

Molecules of calcium hydroxide are held together via ionic bonds between the calcium ion (Ca2+) and two hydroxide ions (OH–). Unprotected exposure to this compound can prove dangerous to humans, leading to irritation of the skin and chemical burns. Exposure to concentrated Ca (OH)2 can lead to lung damage and even blindness.

Physical Properties

  • Ca (OH)2 has a hexagonal crystal structure.
  • It is not very soluble in water and its solubility reduces with an increase in temperature. For example, its solubility at 0 co is 1.89 g/L and its solubility is 1.73 g/L at 20c
  • At temperatures approaching its melting point, this compound tends to lose water and decompose.

Chemical Properties

  • Ca (OH)2 is quite soluble in glycerol and acids, but only slightly soluble in water. When dissolved in water to a saturation point, it yields a solution that acts as a moderate base (called limewater).
  • Limewater (Calcium hydroxide) reacts with acids and forms salts.
  • The saturated solution of calcium hydroxide in water also reacts with and dissolves metals such as aluminum.
  • It reacts with carbon dioxide to form calcium carbonate (CaCO3). This reaction is commonly referred to as carbonatation.

Properties of Calcium Hydroxide

Calcium Hydroxide

Uses of Calcium Hydroxide

  • In the process of sewage treatment, calcium hydroxide is used as a clarifying agent or as a flocculant.
  • Ca (OH)2 is used in the paper industry during the Kraft process of converting wood into wood pulp.
  • It is a very important compound in the preparation of ammonia.
  • This compound is also used as a pH modifier due to its basicity.
  • The pickling of cucumbers is generally done with the help of Ca (OH)2.
  • The production of many plastics involves the use of calcium hydroxide as an ingredient.
  • It is also used in pesticides, hair care products, and the manufacture of ebonite.
  • In root canal procedures, this compound is used to fill the cavities in the human teeth.
  • Sugar beets and sugarcane are processed via carbonation, which involves the use of Ca (OH)2.
  • Calcium hydroxide is used in the leather industry to separate the fur/hair from the animal hide.

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