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Syllabus

Bases (Alkalis)

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Topics

  • Definition: Base
  • Definition: Alkali
Maharashtra State Board: Class 8

Introduction of Base:

Bases are chemical species that have the capacity to donate electrons, accept protons, or release hydroxide ions in an aqueous solution. A base or alkaline is any material that reacts with water to produce OH-. Bases in water often have a pH greater than 7. Because of water's self-ionisation, the solution contains H+ and OH- ions at all times. In simple solutions, there may be more OH⁻ than H⁺.

NaOH (aq)  → Na⁺(aq) + OH⁻(aq)
(Sodium Hydroxide)→(Sodium ion) + (Hydroxide ion)

Some examples of Base

Sr. No. Name of Base Formula Use
1 Sodium hydroxide / Caustic soda NaOH Washing soap
2 Potassium hydroxide / Potash KOH Soap / shampoo
3 Calcium hydroxide / Lime water Ca(OH)₂ Lime / white washing
4 Magnesium hydroxide / Milk of magnesia Mg(OH)₂ Acidity-resistant medicines (Antacids)
5 Ammonium hydroxide NH₄OH For production of fertilizers

Formulas of bases and their uses

Maharashtra State Board: Class 8

Types of bases based on acidity:

It might seem surprising, but bases can also have acidic characteristics. Depending on the number of hydroxyl ions available to combine with hydrogen ions, a base can be classified into 3 types.

  1. Mono Acidic Base: A base with only one hydroxyl ion (OH⁻) that can combine with one hydrogen ion (H⁺) is called a mono acidic base. Examples include NaOH and KOH.
  2. Diacidic Base: A base with two hydroxyl ions (OH⁻) that can combine with two hydrogen ions (H⁺) is known as a diacidic base. Examples are Ca(OH)₂ and Mg(OH)₂.
  3. Triacidic Base: A base containing three hydroxyl ions (OH⁻) that can combine with three hydrogen ions (H⁺) is referred to as a triacidic base. Examples include Al(OH)₃ and Fe(OH)₂.
Maharashtra State Board: Class 8

Types of bases based on therir concentration in aqueous solution:

When a base is diluted, it has a high amount of water and a lower concentration of base material. Concentrated bases have a high percentage of base material and less water, while diluted bases have more water and a lower amount of base. A base can be classified into 2 types:

  1. Concentrated Base: These bases have a high concentration of base material in the solution. For example, a concentrated NaOH solution.
  2. Diluted Base: These bases have a lower concentration of base material in the solution. Examples include dilute NaOH or dilute KOH.
Maharashtra State Board: Class 8

Types of bases based on their degree of ionisation:

This category indicates the strength of a base. A base with a low amount of hydroxyl ions is called a weak base, while a strong base has a high number of hydroxyl ions. Weak bases do not fully dissolve in water. A base can be classified into 2 types: 

  1. Strong Base: A base that fully or almost fully dissociates in water is called a strong base. Examples include NaOH and KOH.
  2. Weak Base: A base that only partially dissolves or dissociates in water is known as a weak base. An example is NH₄OH.
CISCE: Class 10

Definition: Bases

A base is either a metallic oxide or a metallic hydroxide or ammonium hydroxide which reacts with hydronium ions of an acid to form a salt and water only.

CISCE: Class 10

Definition: Alkali

An alkali is a basic hydroxide which when dissolved in water produces hydroxyl (OH-) ions as the only negatively charged ions.

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