Competitive Exams: Oxidation and Reduction
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 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 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
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(NO3)2→ Pbl2 + 2NaNO3
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 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 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