Acids, Bases and Salts

Introduction to Bases

Did you know that most of the fruits and vegetables that we eat are basic in nature? They have an alkaline effect on your body when consumed. Even the soap you use is a base. Let us learn more about bases in chemistry.

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What are Bases?

Bases are substances that slippery to touch when in aqueous form. They taste bitter and change the color of red litmus paper to blue. Bases also dissociate in the water like acids, but instead of producing H+ they produce OH- i.e. hydroxyl ion. If a base dissolves in water then it is called an Alkali. Ammonium hydroxide, Calcium hydroxide are some examples of alkalis. Alkalines become less alkaline when mixed with acids. The pH level of bases ranges from 8-14.

Some examples are caustic soda or sodium hydroxide, calcium hydroxide or limewater, borax. A lot of bleaches, soaps, detergents, kinds of toothpaste, etc are bases.

Properties of Bases

Lithium_alkaline

Some of their properties are

  • Bases are slippery to touch when in aqueous form.
  • A base will usually taste bitter.
  • The pH level of a base is from 8 to 14.
  • Bases react with acid to form salt and water.
  • A Base will turn red litmus to blue.

Classification of Bases

They are usually classified on the basis of strength, concentration and on its acidity.

Classification based on the Strength

Just like acids, the strength of bases depends on the number of hydroxyl ions it produces when dissolved in water. A high amount of hydroxyl ion represents a strong base and a low amount of base represent a weak base.

  • Strong base: A base that dissolves completely or almost completely in water is known as a strong base. For e.g. NaOH, KOH, Ca(OH)2, etc.

NaOH <—> Na+ + OH-

  • Weak base: A base which doesn’t dissolve completely is called a weak base. For e.g. Ma(OH)2, NH4OH

NH4OH(aq) <—-> NH+4(aq) + OH-(aq)

Classification based on the Concentration

The concentration of the base depends upon the amount of base dissolved in water. It is of two types i.e. Concentrated and Dilute base.

  • Concentrated Base: An aqueous solution which has a relatively high percentage of the base is a concentrated base.  For e.g. Concentrated sodium hydroxide, concentrated potassium hydroxide, concentrated ammonium hydroxide, etc
  • Diluted Base: An aqueous solution which has a relatively low percentage of the base is a dilute base. For e.g. dilute sodium hydroxide, diluted potassium hydroxide, dilute ammonium hydroxide, etc.

Classification based on the Acidity of the Base

The acidity of a base depends on the number of hydroxyl ions it contains. It also depends on the number of hydrogen ions with which a base can combine as one hydrogen ion combines with one hydroxyl ion. It is usually of three types Monoacidic base, Diacidic base, and Triacidic base.

  • Monoacidic base: It is a base that consists only one hydroxyl ion and only combines with one hydrogen ion. For e.g. NaOH, KOH, NH4OH, etc

NaOH(aq) + HCl(aq) <—> NaCl(aq) + H2O(l)

  • Diacidic base: It is a base that contains two hydroxyl ions and combines with two hydrogen ions. For e.g. Mg(OH)2, Fe(OH)2, Zn(OH)2, etc.

Ca(OH)2(aq) + 2HCl(aq) <—> CaCl2(aq) + 2H2O(l)

  • Triacidic base: It is a base that has three hydroxyl ions and combines with three hydrogen ions. For e.g. Aluminium Hydroxide.

Al(OH)3(aq) + 3HCl(aq) <—> AlCl3(aq) + 3H2O(l)

Solved Example for You

Q: Alkalis are which of the following

  1. weak acids
  2. strong acids
  3. weak base
  4. strong base

Sol: The correct answer is option ‘d’. Alkalis are water-soluble bases. They completely dissociate into hydroxide ions in aqueous medium. Hence they are strong bases.

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