NET, IAS, State-SET (KSET, WBSET, MPSET, etc.), GATE, CUET, Olympiads etc.: Oxidation and Reduction

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Oxidation and Reduction

  • Removal of hydrogen atom is oxidation while addition of hydrogen atom is reduction.
  • Addition of oxygen atom is oxidation while removal of oxygen atom is reduction.
  • Increase in valence of an element is oxidation while decrease in valence of an element is reduction.
  • Addition of an electronegative element is oxidation and removal is reduction.
  • Loss of electrons is oxidation and gain of electrons is reduction.
  • Increase in oxidation number is oxidation while decrease in oxidation number is reduction.

Oxidizing and Reducing Agents

  • Compounds having higher oxidation number will be more acidic and act as oxidizing agent and compounds having lower oxidation number will be less acidic and act as reducing agent.
  • Generally, compounds with oxygen atom are called oxidizing agent and compounds with hydrogen atom are called reducing agent.
  • H2O2 acts as a reducing agent when it is oxidized to O2 or O3.
  • H2S acts as a reducing agent when it is oxidized to sulphur.
  • Halogens act as oxidizing agent and they are reduced to halogen acids.

Chemical Changes⟋Reactions in Chemistry

Combination Reaction

Combination reaction occurs when two substances unite to form a third substance.

For example, combining magnesium Mg and oxygen O2 result in the production of magnesium oxide MgO

2Mg + O2 ⇾ 2MgO

Decomposition Reaction

Decomposition reaction occurs when a single compound breaks down into two or more simpler substances.

In the decomposition of mercuric oxide HgO , the elements mercury Hg and oxygen O2 are produced

2HgO ⇾ 2Hg + O2

Displacement Reaction

When one element replaces another in a compound, it is known as a displacement reaction.

For example, iron Fe may displace copper Cu in a solution of cupric sulphate CuSO4

Fe + CuSO4 ⇾ FeSO4 + Cu

Double Decomposition Reaction

When two compounds interact to form two other compounds, it is known as a double decomposition reaction.

For example, sodium iodide Nal and lead nitrate PbNO3) react to form lead iodide (PbI2 and sodium nitrate

2NaI + Pb NO32 ⇾ Pbl2 + 2NaNO3

Hydrolysis

Hydrolysis is a double decomposition reaction in which water reacts with a second substance.

When ammonium chloride NH4Cl) is combined with water (H2O) , it undergoes hydrolysis, yielding ammonium hydroxide NH4OH and hydrochloric acid HCl .

NH4C1 + H2O ⇾ NH4OH + HCl

Neutralization Reaction

Neutralization is the interaction of an acid with an equivalent quantity of a base.

If the process is carried out in an aqueous solution (dissolved in water) , the products are water and a salt.

For example, hydrochloric acid (HCl) and sodium hydroxide (NaOH) neutralize each other when dissolved in water, forming sodium chloride (NaCI) , a salt, and water

HCl + NaOH ⇾ NaCI + H2O

Substitution Reaction

Substitution reaction occurs when an element, such as chlorine Cl , replaces one or more hydrogen atoms in a hydrocarbon, such as methane CH4

CH4 + Cl2 ⇾ CH3Cl + HCl