What are alkalis?

Short Answer

Alkalis are a special group of bases that dissolve in water. When they dissolve, they release hydroxide ions (OH⁻), which make the solution basic or alkaline. Common alkalis include sodium hydroxide, potassium hydroxide, and calcium hydroxide. These substances feel slippery, taste bitter, and turn red litmus paper blue.

Alkalis are widely used in soaps, detergents, cleaning agents, and many industrial processes. Although some alkalis are safe in small amounts, many strong alkalis can be harmful or corrosive. Their ability to dissolve in water and release hydroxide ions is what makes them different from other bases.

Detailed Explanation :

Alkalis

Alkalis are an important category of chemical substances. They belong to the family of bases, but not all bases are alkalis. Only those bases that dissolve in water to release hydroxide ions (OH⁻) are called alkalis. In simple terms, all alkalis are bases, but all bases are not alkalis. This means an alkali is a water-soluble base. The word “alkali” comes from an Arabic term meaning “ashes of plants,” because early alkalis were made from plant ashes rich in potassium and sodium compounds.

Alkalis play a major role in daily life and industries. They are used in making soap, detergents, medicines, paper, and many other materials. However, strong alkalis must be handled carefully because they can cause burns or damage surfaces.

Meaning of Alkalis

An alkali is defined as a base that dissolves in water and produces hydroxide ions (OH⁻). Bases like sodium hydroxide (NaOH), potassium hydroxide (KOH), and calcium hydroxide (Ca(OH)₂) are common examples of alkalis. They behave similarly to bases but have an additional property: they are soluble in water. When an alkali dissolves, its ions separate, which allows the solution to show typical basic properties.

Formation of Hydroxide Ions

A key feature of alkalis is their ability to release hydroxide ions in water. For example:

  • Sodium hydroxide → Na⁺ + OH⁻
  • Potassium hydroxide → K⁺ + OH⁻

These hydroxide ions give the solution its basic character. Because of this, alkalis can neutralise acids, react with metals, and change the colour of indicators. The larger the number of hydroxide ions in a solution, the stronger the alkali.

Properties of Alkalis

Alkalis have several clear and common properties that make them easy to identify:

  1. Soluble in Water

Unlike many bases, alkalis dissolve easily in water. This solubility helps them spread quickly in water and show their basic nature.

  1. Release Hydroxide Ions

Aqueous alkali solutions contain OH⁻ ions, which make them alkaline.

  1. Bitter Taste and Slippery Touch

Alkalis usually taste bitter and feel slippery because they react with oils on the skin. However, tasting or touching strong alkalis is unsafe.

  1. Change Colour of Indicators

Alkalis turn red litmus paper blue. They also change the colour of other indicators. For example, phenolphthalein turns pink in the presence of alkalis.

  1. Reaction with Acids

Alkalis neutralise acids to form salt and water. This reaction is important in daily life, laboratories, and industries.

  1. Electrical Conductivity

Alkali solutions conduct electricity because they contain free ions.

  1. Corrosive Nature

Strong alkalis like sodium hydroxide and potassium hydroxide are corrosive and can damage skin, metals, and fabrics.

Examples of Alkalis

Some of the most common alkalis are:

  • Sodium hydroxide (NaOH): Used in soaps and cleaning agents.
  • Potassium hydroxide (KOH): Used in batteries and fertilizers.
  • Calcium hydroxide (lime water): Used in whitewashing and testing for carbon dioxide.
  • Ammonium hydroxide (NH₄OH): Used in household cleaners and laboratories.

These alkalis differ in strength, but all release hydroxide ions when dissolved in water.

Uses of Alkalis

Because of their special properties, alkalis are used widely in many fields:

  1. Soap and Detergent Making

Sodium hydroxide and potassium hydroxide are used to make soaps and detergents. They help break down oils and dirt.

  1. Cleaning Products

Many household cleaners contain mild alkalis like ammonium hydroxide. They help remove stains and grease.

  1. Agriculture

Alkalis are used to adjust soil pH and improve crop growth.

  1. Paper, Textiles, and Industry

Sodium hydroxide is used in the production of paper, textiles, and plastics.

  1. Medicine and Food Processing

Some alkalis, like magnesium hydroxide, are used in antacid medicines. Calcium hydroxide is used in processing sugarcane juice.

Difference Between Bases and Alkalis

  • Bases are substances that can accept hydrogen ions or produce hydroxide ions.
  • Alkalis are a subgroup of bases that dissolve in water.

A base like copper oxide is not an alkali because it does not dissolve in water. Sodium hydroxide is an alkali because it does dissolve and release hydroxide ions.

Conclusion

Alkalis are water-soluble bases that release hydroxide ions when dissolved in water. They show properties such as bitter taste, slippery feel, ability to turn red litmus blue, and capacity to neutralise acids. Common alkalis like sodium hydroxide, potassium hydroxide, and calcium hydroxide are widely used in households, industries, agriculture, and medicine. Understanding alkalis helps us recognise how these substances behave and how they are applied in everyday life.