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