Calcium Hydroxide

Introduction

Calcium hydroxide is a white powder or crystalline and has a chemical formula Ca(OH)₂. It is also known by the name slaked lime, hydrated lime, builders’ lime, pickling lime, caustic lime, etc. The saturated solution of calcium hydroxide is known as milk of lime. It is used in sewage treatment, for balancing the pH level of soil, in food industries, juices, as a fungicide, paper production, medical treatment, etc. It is produced through hydrated calcium oxide and has many applications like disinfectant, pH modifier, additive in animal feeds, sugar industry, and water treatment.

What is Calcium Hydroxide?

Calcium di hydroxide is an odourless colourless in crystalline form and white appearance in fine form. It is an inorganic compound obtained by the reaction of calcium oxide and water. It is an exothermic reaction. It is produced by the thermal decomposition of limestone i.e., calcium carbonate, then calcium oxide reacts with water and produces calcium hydroxide. The energy released during the reaction is enough to evaporate water.

$$\mathrm{CaCo_3 → CaO + CO_2}$$

$$\mathrm{CaO + H_2 O → Ca(OH)_2+65.2\: KJ\: energy.}$$

Calcium Carbonate Cycle

Peter Bell, The lime cycle, CC BY-SA 3.0

Calcium Hydroxide Explained

Calcium Hydroxide is represented by a chemical formula Ca(OH)_2. In this, the calcium ion Ca^(2+)and two hydroxide ions OH^- are bonded together by an ionic bond. It is also prepared by the reaction of an aqueous solution of calcium chloride and sodium hydroxide.

$$\mathrm{CaCl_2+2NaOH → Ca(OH)_2+ 2NaCl}$$

Calcium Hydroxide

Properties of Calcium Hydroxide

Calcium di hydroxide is an inorganic compound. A drench solution of calcium hydroxide is known as milk of lime or lime water.

Properties	Attribute
IUPAC Name	Calcium Hydroxide
Common Names	Milk of Lime, Slaked Lime, Pickling Lime, Portlandite, Calcium Di-hydroxide, etc.
Structure	Hexagonal crystals

Physical Properties

Physical Properties	Attributes
Semblance	White powder
Odour	Odourless
Density	2.211 g/cm3
Melting Point	580oC
Solubility	Slightly soluble in water but soluble in acids, glycerols, and insoluble in ethanol.
Molar Mass	74.09 g/mol
Taste	Slightly bitter

Chemical Properties

The chemical properties of calcium hydroxide are as follows.

• Reaction with Carbon dioxide − when calcium hydroxide reacts in presence of carbon dioxide it turns milky due to the formation of calcium carbonate and releases water. This is known as a carbonation reaction.

  $$\mathrm{Ca(OH)_2+ CO_2 → CaCO_{3}+ H_2 O}$$

• Decomposition of Calcium di Hydroxide − When it is heated at 512^oC, it decomposes to calcium oxide and water.

  $$\mathrm{Ca(OH)_2 → CaO + H_2 O}$$

• The suspension of Ca(OH)₂ in water is known as milk of lime. Calcium Hydroxide is slightly soluble in water, around 0.16 gm in 100gm of water at 20^oC. Its solubility in water decreases as the temperature increases.

Why is Calcium Hydroxide less soluble in Water?

Calcium hydroxide is less soluble in water. The calcium di hydroxide is formed by the small hydroxide anions OH^-and small cations of calcium Ca²⁺, these both are small ions. Small ions bind more strongly than one small and one big ion. It's easy to break the compounds formed by one small and big ion. The bond present in calcium dihydroxide is ionic due to the smaller size of slaked lime. It is strong as a covalent bond so does not dissociate easily. Another reason is due to the decrease in the lattice energy in hydroxide ions, it did not dissolve easily in water.

Uses of Calcium Hydroxide

Calcium dihydroxide is used for various commercial purposes like in food, sugars, fortified juices, medicinal purposes, etc. Some of the uses are as follows.

• Use of Calcium dihydroxide in the preparation of ammonia gas,

  $$\mathrm{2NH_4 Cl + Ca(OH)_2 → 2NH_3+CaCl_2+2H_2}$$

• It is used as an intermediate in the making of sodium hydroxide in the process of making pulp in the paper manufacturing industry.

• It is used as a fungicide in orchard crop production.

• In sewage and water treatment, it is used as a flocculant. It forms a solid that helps remove smaller particles from water.

• It is also used as a pH corrector for decreasing the acidity in the soil.

• It is used as a pickling agent in pickles to give it extra crunch in cucumber or vegetables.

• It is also used for medicinal purposes like in root canals it is used for capping and as filler.

• It is widely used in the leather industry to remove hairs from the skin of animals.

Native American Uses

In Native America, calcium hydroxide is known as nextli in the Aztec language. It is used there in the process of nixtamalization, i.e., maize is cooked with calcium hydroxide to form nixtamal or hominy. This process increases the niacin (Vitamin B3) level in the maize. It increases its nutritional value and makes it easy to digest.

• Nixtamal is used to make flour, which is known as Masa from which tortillas and tamales are made.

• In America it is chewed with coca leaves, to increase absorption of coca leaves due to their high alkaline value.

• It is also chewed with tobacco leaves by tribes of native America to enhance its effect.

Conclusion

We have studied that calcium hydroxide is an inorganic, tasteless, colourless, and odourless solid. It is alkaline and has a high pH value. It is widely used commercially in food industries, paper and leather industries, and the medical field. It is used as filler to fill cavities in teeth and during the root canal process. It is also used in the food industry like in fortified juices, baby milk formula, for clearing brine, and for processing of water used in alcoholic and soft drinks. In native America, it is used to prepare nixtamal and chewed with tobacco leaves to enhance nutrients and flavours.

FAQs

1. What happens if the overdose of calcium di-hydroxide is taken?

If you have taken an overdose of calcium hydroxide it can cause serious health issues like breathing problems, hypertension, internal bleeding, skeletal muscle paralysis, and internal organ failure.

2. What is the pH of Calcium hydroxide?

The pH of calcium dihydroxide is 12.8 and alkaline. It is a strong base.

3. What is the role of calcium dihydroxide in maintaining the pH level of Soil?

It is used as a pH corrector in soil. It is dissolved in water and sprinkled on the soil surface which reduces the acidity in the soil and maintains the pH level of the soil.

4. What is portland cement?

Portland cement is made up of four ingredients named: tricalcium silicate, dicalcium silicate, tricalcium aluminate, tetra-calcium alumino-ferrite, and a small amount of uncombine lime and magnesia.

5. How is Calcium Hydroxide used in the sugar industry?

Calcium hydroxide is used for the carbonation process in the sugar industry. It is added in an untreated sugar solution that removes the impurities and improves the stability of the solution.