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Calcium Hydroxide

Last updated date: 09th Apr 2024
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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.


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 centimeter

Molecular Weight or Molar Mass

74.093 grams per mole

Melting Point


Appearance or Color of calcium hydroxide or calcium hydroxide color

Colorless 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 carbonation.

Why is Calcium Hydroxide less Soluble in Water?

Calcium hydroxide is also known as slaked lime in general is less soluble in water but, when its temperature is increased, it starts reaching its melting point and decomposes its material. The reason for this less solubility is due to a decrease in the lattice energy in hydroxide salts. The solution formed by the reaction of calcium hydroxide and water is called milk of lime. Unlike water, Calcium hydroxide is easily soluble in acids and glycerol hence, it is used as a pH corrector to reduce a solution’s acidity. 

Calcium hydroxide is added to water and sprayed on the soil to correct its pH level and recover the soil, it is also used in the construction of roadways and railways. But, adding it to the soil along with other fertilizers containing ammonium phosphate will reduce the nitrogen content of the soil. But, direct contact with Calcium hydroxide is harmful to humans and might cause loss of vision, so the US has banned adding Calcium hydroxide to the soil. Due to its pH value, Calcium hydroxide is also used as an antacid to treat burns and wounds caused by acids. Even the solution obtained from Calcium hydroxide and water also known as milk of lime is used as an antacid to treat burns and acid wounds.

Uses of Calcium Hydroxide

There are many different uses of calcium hydroxide, and 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 cucumber 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 root canal procedures, this compound is used in filling the human teeth cavities.

  • We can use it in pesticides, manufacturing of ebonite, and 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 mollusk 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.

FAQs on Calcium Hydroxide

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

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?

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?

Calcium hydroxide is also known as slaked lime in general. It is in white when it is in a solid-state and colorless when it is in crystallized form.  The 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.


It can also be formed by mixing calcium chloride, sodium hydroxide in water, this chemical reaction also gives us calcium hydroxide as one of the resultant compounds. Unprotected exposure, direct contact with concentrated calcium hydroxide, results in irritation of eyes, damage to lungs and sometimes even leads to blindness. This compound is less soluble in water but when the temperature of the solution increases, it starts mixing up with the water. 


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.

Calcium hydroxide is formed by mixing water and calcium oxide also known as quicklime. It is white when it is in a solid-state and colorless when it is in crystallized form. 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 naswar 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.

5. What are the general uses of calcium hydroxide?

Calcium hydroxide, also known as slaked lime in general, is represented as Ca(OH)2 and it is an inorganic compound. When it is in the solid-state, it is white and when it is crystallized, it is colorless. It is formed by mixing water and quicklime i.e, calcium oxide. Following are some general uses of calcium hydroxide:

  • Paper is manufactured from the wood pulp of some trees. To convert wood into pulp in a kraft process, calcium hydroxide is used.

  • Even in the sewage cleaning process, calcium hydroxide is used as a clarifying agent or to form the clumps in the waste matter for cleaning it easily. 

  • Calcium hydroxide reacts with ammonium chloride to give ammonia, hence, it is an important component in manufacturing ammonia.

  • Calcium hydroxide is also used to pickle cucumbers in daily life.

  • Calcium hydroxide is basic and hence, it is used as a pH corrector.

  • Calcium hydroxide is also used in plastics manufacturing industries.

  • In dentistry, this compound is used to fill the root canals as it is odorless.

  • Calcium hydroxide is also used in hair care products, pesticides etc, 

  • Sugarcane is processed by carbonation in which Calcium hydroxide plays an important role. 

  • In some countries like India, Pakistan and Afghanistan, calcium hydroxide is added to betel leaves to make “Paan” and it helps in keeping alkaloid stimulants available to the human body.

  • Calcium hydroxide is also used as paint on mud houses in these countries and some Native American countries, it is used to make psychedelic substances. It is also cooked along with maize in these countries to improve the vitamin B3 content. 

  • In bakeries, calcium hydroxide is used as a substitute for baking soda, it is claimed that calcium hydroxide improves digestion. It is an important ingredient in manufacturing cement, mortar and plasters that are used in construction. 

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