Calcium Hydroxide | Definition, Formula, Molar Mass, Uses and Properties

Calcium hydroxide is a chemical compound with the chemical formula Ca(OH)2. It is also called slaked lime or hydrated lime. It is odorless with white powder or crystal with a slightly bitter taste. Calcium hydroxide is a strong base with a pH of 12-13 and is slightly soluble in water.

Calcium Hydroxide Formula

Calcium hydroxide, which has the chemical formula Ca(OH)2, contains one calcium ion (Ca2+) and two hydroxide ions (OH-) per formula unit. 

The chemical structure of calcium hydroxide consists of a calcium ion (Ca2+) surrounded by two hydroxide ions (OH-) that are attached to each calcium ion via ionic bonds.

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Calcium Hydroxide Molar Mass 

The mass of calcium hydroxide is about 74.1 g/mol.

The molar mass of calcium hydroxide (Ca(OH)2) is calculated by adding the atomic masses of the constituent atoms together. 

Calcium Hydroxide | Definition, Formula, Molar Mass, Uses and Properties

Atomic mass of calcium (Ca) is 40.08 g/mol.

Atomic mass of oxygen (O) is 16.00 g/mol. 

Atomic mass of hydrogen (H) is 1.01 g/mol.

Calculated the molar mass of calcium hydroxide (Ca(OH)2)

Molar mass = (1 × atomic mass of calcium) + (2 × atomic mass of oxygen) + (2 × atomic mass of hydrogen)

Molar mass = (1 × 40.08 g/mol) + (2 × 16.00 g/mol) + (2 × 1.01 g/mol)

Molar mass = 40.08 g/mol + 32.00 g/mol + 2.02 g/mol

Molar mass = 74.10 g/mol.

Calcium Hydroxide Properties

Physical Properties

Appearance: It is a white-colored, and odorless powder.

Crystal structure: The calcium hydroxide structure is a hexagonal shape.

pH: Calcium hydroxide occurs between 12-13.

Boiling point: It does not have a boiling point because it decomposes before reaching its boiling point.

Melting point: The melting point is around 580°C.

Solubility: It is slightly soluble in water with a solubility of approximately 1.7 g/liter at room temperature.

Density: Its density is about 2.21 g/cm³.

Chemical Properties

Basicity: It is a strong base and can react with acids. For example, when it reacts with hydrochloric acid (HCl), it forms calcium chloride (CaCl2) and water (H2O).

 Ca(OH)2 + 2HCl → CaCl2 + 2H2O

Reaction with carbon dioxide: This calcium reacts with carbon dioxide (CO2), and the hydroxide forms calcium carbonate (CaCO3), a white solid known as a white powder or chalky buildup. 

Ca(OH)2 + CO2 → CaCO3 + H2O

Rect with Aluminium: Saturated solution of this Ka reacts with metals like aluminum and dissolves them.

Calcium Hydroxide Uses 

It is used in the production of cement and mortar. 

For the production of pickling lime for canning and preservation of foods is used. 

It is used as a flocculating agent in water treatment. 

It is used to prepare some chemicals including calcium stearate and calcium phosphate. 

It is used as an antacid to neutralize stomach acid. 

These are used as soil amendments to raise the pH of acidic soils.

How is Calcium Hydroxide Prepared?

Calcium hydroxide (Ca(OH)2) is prepared by adding water to calcium oxide (CaO), a process called slaking. The reaction is exothermic and a large amount of heat and energy is produced.

When calcium oxide reacts with water 

CaO + H2O → Ca(OH)2

The resulting calcium hydroxide suspension is filtered to remove any impurities and dried to obtain the final product.


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