Calcium Hydroxide

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What is Calcium Hydroxide?

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

The other names of this compound can be given as slack lime, hydrated lime, caustic lime, and pickling lime. In general, the calcium hydroxide is prepared by mixing calcium oxide (which is also called quicklime) and water.

Calcium Hydroxide Explained

Also, the chemical reaction between the calcium chloride and sodium hydroxide dissolved in water (aqueous CaCl2) yields this compound. The structural representation of a Ca(OH)2 molecule can be illustrated below.

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The calcium hydroxide molecules are held together by ionic bonds between the two hydroxide ions (OH) and calcium ions (Ca2+). Unprotected exposure to this compound may prove dangerous to humans by leading to skin irritation and chemical burns. Exposure to the concentrated Ca(OH)2 can lead to damage to the lungs and even blindness.

A few of the important properties of calcium hydroxide can be tabulated as follows:

Properties of Calcium Hydroxide


Calcium Hydroxide

Chemical Formula for calcium hydroxide symbol or Calcium Hydroxide formula



2.211 grams/cubic centimetre

Molecular Weight or Molar Mass

74.093 grams per mole

Melting Point


Appearance or Colour of calcium hydroxide or calcium hydroxide colour

Colourless crystal or White powder

Physical Properties

Let us look at a few of the physical properties of calcium hydroxide as listed below:

  • Ca(OH)2 has a structure of hexagonal crystals.

  • This compound is not very soluble in water. But, its solubility reduces with an increase in temperature. For suppose, its solubility at solubility is 1.73 g/L at 20℃ and at 0℃ is 1.89 g/L.

  • This compound also tends to lose water and decompose at temperatures approaching its melting point.

  • The solubility product (Ksp) of the calcium hydroxide can be given as 5.5 * 10-6.

Chemical Properties

Let us look at a few of the chemical properties of calcium hydroxide, as listed below.

  • The calcium hydroxide is quite soluble in acids and glycerol, but it is slightly soluble only in water. It yields a solution that acts as a moderate base (called limewater) when it is dissolved in water to a saturation point.

  • The lime water reacts with acids and forms salts.

  • The saturated calcium hydroxide solution in water also reacts with and dissolves the metals such as aluminum.

  • It also reacts with carbon dioxide and forms calcium carbonate (CaCO3). In general, this reaction can be referred to as carbonatation.

Uses of Calcium Hydroxide

There are many different uses of calcium hydroxide, where a few of them are listed below. Let us have a look at those.

  • Ca(OH)2 can be used in the paper industry during the Kraft process, which converts wood into wood pulp.

  • In the sewage treatment process, calcium hydroxide can be used as a flocculant or clarifying agent.

  • It is an important compound in ammonia preparation.

  • Generally, the cucumbers pickling is done with the help of Ca(OH)2.

  • Also, this compound is used as a pH modifier because of its basicity.

  • The production of various plastics involves the use of calcium hydroxide as a primary ingredient.

  • In the root canal procedures, this compound is used in filling the human teeth cavities.

  • We can use it in pesticides, manufacturing of ebonite, and in hair care products.

  • Calcium hydroxide can be used in the leather industry to separate the fur or hair from the animal hide.

  • Sugarcane and Sugar beets are processed via carbonation, which involves the use of Ca(OH)2.

Native American Uses

In Spanish, the calcium hydroxide compound is known as cal. Maize cooked with cal (in a nixtamalization process) becomes hominy (nixtamal), which increases the bioavailability of niacin (vitamin B3) significantly, and also it is considered tastier and quite easier to digest.

Calcium hydroxide is usually chewed alongside chewing coca leaves to keep the alkaloid stimulants available chemically for absorption by the body. In the same way, the Native Americans chewed tobacco leaves traditionally with calcium hydroxide derived from the burnt mollusc shells to enhance its effects. Also, it has been used by a few indigenous American tribes as the main ingredient in yopo, which is a psychedelic snuff prepared from the beans of some species of Anadenanthera.

FAQ (Frequently Asked Questions)

1. Justify Calcium Hydroxide, Whether it is Acidic or Basic?

Ans: Calcium hydroxide is also called slaked lime (having the chemical formula Ca(OH)2). It is a hydroxide ion source when dissolved in aqueous solutions. Thus, this is a base compound. Due to the electrolyte dissociation, this compound liberates the OH- ions.

2. How is Calcium Hydroxide Applied in Dental and Medical Application?

Ans: Calcium hydroxide is a white powdered compound that does not contain any characteristic odor. Also, there are various dental and medical applications of this compound. For example, fillings that are used in the root canal treatments often contain calcium hydroxide.

3. How is Calcium Hydroxide Prepared?

Ans: Calcium hydroxide compound is formed by the action of water on calcium oxide, which is also called slaked lime (Ca(OH)2). A lesser proportion of it dissolves when it is combined with water, forming a solution called limewater, the remainder remaining in a suspension known as lime milk.

Therefore, the important properties and the structure of calcium hydroxide are discussed, along with a few of its uses.

4. Provide Some Asian Uses of Calcium Hydroxide.

Ans: Typically, calcium hydroxide is added to a bundle of betel leaf called 'paan' and areca nut to keep the alkaloid stimulants available chemically to enter the bloodstream through sublingual absorption.

It is also used in making naswar (which is otherwise called niswar or nass), a type of dipping tobacco that is made from fresh tobacco leaves, wood ash, and calcium hydroxide (soon or chuna). Mostly, it is consumed in Afghanistan, Pathan diaspora, Pakistan, Bangladesh, and India. Some villagers also use these calcium hydroxide compounds to paint their mud houses in Afghanistan, Pakistan, and India.