Calcium Hydroxide: Physical and Chemical Properties and Uses

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Discover the physical and chemical properties of calcium hydroxide and explore its diverse range of uses in our informative notes on Calcium Hydroxide.

Calcium Hydroxide: The Nature of Slaked Lime

  • Calcium hydroxide, commonly known as slaked lime, is denoted by the chemical formula Ca(OH)2.
  • In its solid state, this inorganic compound presents itself as a white, powdery substance. However, its crystalline form appears colorless.

Other Names and Preparation

  • This compound is also recognized by various names such as hydrated lime, slack lime, pickling lime, and caustic lime.
  • Typically, the preparation of calcium hydroxide involves the combination of water with calcium oxide, also referred to as quick lime.
  • Another method involves a chemical reaction between sodium hydroxide and calcium chloride in aqueous CaCl2.

Molecular Structure

  • The molecular structure of Ca(OH)2 involves the bonding of calcium ions (Ca2+) with two hydroxide ions (OH) through ionic bonds. This arrangement forms the stable calcium hydroxide molecule.

Safety Considerations

  • Caution is advised when handling calcium hydroxide as unprotected exposure can pose risks. It has the potential to irritate the skin and chemical burns.
  • Exposure to concentrated Ca(OH)2 can result in severe consequences such as lung damage and, in extreme cases, even blindness. Understanding and implementing proper safety measures are crucial when dealing with this compound.

Properties of Calcium Hydroxide

Chemical FormulaCa(OH)2
IUPAC nameCalcium Hydroxide
Molecular Weight/Molar Mass74.093 grams per mole
Density2.211 grams per cubic centimetre
AppearanceWhite powder or colourless crystal
Melting Point853 K

Physical Characteristics of Calcium Hydroxide

Crystal Structure

The crystal structure of Ca(OH)2 is characterized by a hexagonal arrangement.

Solubility in Water

Calcium hydroxide exhibits limited solubility in water, and this solubility diminishes as the temperature rises.

For instance, at 0°C, its solubility is 1.89 g/L, and at 20°C, it further decreases to 1.73 g/L.

Thermal Behavior

As temperatures approach the melting point, Ca(OH)2 tends to undergo dehydration, releasing water and decomposing in the process.

Solubility Product

The solubility product (Ksp) of calcium hydroxide is recorded at 5.5 × 10-6, indicating the equilibrium constant for its limited solubility in aqueous solutions. Understanding these physical properties is crucial for comprehending the behavior of calcium hydroxide under different conditions.

Chemical Behavior of Calcium Hydroxide

Solubility in Various Solvents

While calcium hydroxide exhibits notable solubility in glycerol and acids, its solubility in water is relatively limited.

Formation of Limewater

When dissolved in water to its saturation point, calcium hydroxide produces a solution known as limewater. This solution behaves as a moderate base and is commonly utilized in various chemical processes.

Reactivity with Acids

Limewater, derived from calcium hydroxide, reacts with acids to produce salts. This chemical interaction exemplifies the compound’s acidic neutralization properties.

Interaction with Metals

The saturated solution of calcium hydroxide in water displays reactivity with metals, including metals like aluminum, leading to the dissolution and formation of corresponding salts.

Carbonatation Reaction

In the presence of carbon dioxide, calcium hydroxide undergoes a reaction known as carbonatation, resulting in the formation of calcium carbonate (CaCO3).

This chemical transformation is essential in various industrial processes and contributes to the compound’s versatile applications.

Read More: Calcium Carbonate, Formula, Properties, Uses, Application

Applications of Calcium Hydroxide

Sewage Treatment

In sewage treatment, calcium hydroxide plays a crucial role as a clarifying agent and flocculant, aiding in the removal of impurities.

Paper Industry

The paper industry utilizes Ca(OH)2 in the Kraft process, where it contributes to the conversion of wood into wood pulp.

Ammonia Production

Calcium hydroxide is a vital component in the preparation of ammonia, contributing to the synthesis of this essential chemical compound.

pH Modification

Due to its basic properties, Ca(OH)2 serves as a pH modifier in various applications, helping to adjust acidity levels.

Pickling Agent

The pickling of cucumbers involves the use of Ca(OH)2, contributing to the preservation and flavor enhancement of this popular food item.

Plastics Production

In the manufacturing of plastics, calcium hydroxide is employed as an ingredient, playing a role in the production of diverse plastic materials.

Diverse Industries

Its applications extend to pesticides, hair care products, and the production of ebonite, showcasing its versatility in different industrial processes.

Dental Procedures

In dentistry, specifically in root canal procedures, calcium hydroxide is utilized to fill cavities in human teeth.

Sugar Processing

Sugar beets and sugarcane undergo processing through carbonation, a process that involves the use of Ca(OH)2.

Leather Industry

In the leather industry, calcium hydroxide is employed to separate fur/hair from animal hides, contributing to the leather processing procedures. Understanding these varied applications underscores the significance of calcium hydroxide across diverse industrial sectors.

Frequently Asked Questions (FAQs) About Calcium Hydroxide

Q1. What are the common uses of calcium hydroxide?

Calcium hydroxide, a white powder without a distinct odor, finds application in various industries. It is utilized in waste treatment, paper manufacturing, construction, and food processing, and has medical and dental applications. For example, it is often present in fillings used during root canal treatments.

Q2. Is calcium hydroxide acidic or basic?

Calcium hydroxide, also known as slaked lime (Ca(OH)2), acts as a base. When dissolved in water, it releases hydroxide ions (OH-) due to electrolyte dissociation.

Q3. How is calcium hydroxide prepared?

Calcium hydroxide is produced by combining water with calcium oxide, also called slaked lime (Ca(OH)2). This process results in the formation of a solution known as limewater, along with a suspension called lime milk.

Q4. Is calcium hydroxide ionic or covalent?

Calcium hydroxide has an ionic structure.


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