Oxidation is a process in which electrons are lost, oxygen is added, or hydrogen is removed during a reaction by a molecule, atom, or ion. In contrast, Reduction is a process in which electrons are gained, oxygen is removed, or hydrogen is added during a reaction by a molecule, atom, or ion.
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Definition: In oxidation and reduction reactions, electrons are transferred in the reactants. If a reactant loses an electron, it is known as oxidation, while if the reactant gains an electron, it is known as reduction. |
Oxidation and Reduction Chemistry Questions with Solutions
Q1. The reaction in which oxidation and reduction co-occur is known as
(a) Redox reaction
(b) Oxiduction reaction
(c ) Both a and b
(d) None of the above
Answer: (a) The reaction in which oxidation and reduction co-occur is known as a redox reaction.
Q2. Oxidation refers to the
(a) Gain of electrons
(b) Loss of electrons
(c ) Loss of protons
(d) Gain of protons
Answer: (b) Oxidation refers to the loss of electrons.
Q3. Reduction refers to the
(a) Gain of electrons
(b) Loss of electrons
(c ) Loss of protons
(d) Gain of protons
Answer: (b) Reduction refers to the gain of electrons.
Q4. The addition of oxygen from a compound is an example of ________?
(a) Reduction
(b) Oxidation
(c) Dehydrogenation
(d) Oxygenation
Answer: (b) The addition of oxygen from a compound is an example of oxidation.
Q5. The addition of hydrogen from a compound is an example of ________?
(a) Reduction
(b) Oxidation
(c) Dehydrogenation
(d) Oxygenation
Answer: (a) The addition of hydrogen from a compound is an example of reduction.
Q6. What is the oxidation number of chlorine in MgCl2?
Answer: The oxidation number of chlorine in MgCl2 will be:
x + 2 X ( – 1) = 0
x – 2 = 0
x = 2
Q7. How many moles of K2Cr2O7 are needed to react with one mole of H2S in an acidic medium?
Answer: Chemical Equation: K2Cr2O7 + 4 H2SO4 + 3 H2S → K2SO4 + Cr2(SO4)3 + 7 H2O + 3 S
1 mol of potassium dichromate reacts with 3 moles of hydrogen sulfide.
Hence, the number of moles of K2Cr2O7 that will be needed to react with one mole of H2S in an acidic medium is 1 / 3.
Q8. Consider the following reaction:
6 NaOH + 3 Cl2 → 5 NaCl + A + 3 H2O
What is the oxidation number of chlorine in A?
Answer: Here, A is NaClO3.
6 NaOH + 3 Cl2 → 5 NaCl + NaClO3 + 3 H2O
The oxidation number of chlorine in NaClO3 will be:
1 + x + 3 X ( – 2) = 0
1 + x – 6 = 0
x – 5 = 0
x = 5.
Q9. How many electrons are involved in the following redox reaction?
Cr2O72− + Fe2+ + C2O42− → Cr3+ + Fe3+ + CO2
Note: The reaction is not balanced.
Answer: Foremost, we will balance the equation.
Cr2O72− + 2 Fe2+ + 2 C2O42− → 2 Cr3+ + 2 Fe3+ + 4 CO2
The oxidation number of chromium is + 6 in Cr2O72− , reducing to + 3 in Cr3+. On balancing the equation, we will notice that 2 moles of chromium ion go from +6 to +3.
Hence, 6 electrons are involved in the overhead redox reaction.
Q10. Name the reagent that can be used to reduce Fe3+ to Fe2+.
Answer: We can use H2O2 in the presence of NaOH or Na2O2 in water to reduce Fe3+ to Fe2+.
Q11. Name the element that never shows a positive oxidation number.
Answer: Fluorine never shows a positive oxidation number.
Q12. Give examples of oxidation reactions that you encounter in your daily life.
Answer: Rusting of iron and rotting of wood are examples of oxidation reactions that we encounter daily.
Q13. What is oxidation?
Answer: Oxidation is a process in which electrons are lost, oxygen is added, or hydrogen is removed during a reaction by a molecule, atom, or ion.
Example: Fe (s) + O2 (g) ⟶ Fe2O3 (g)
Q14. What is reduction?
Answer: Reduction is a process in which electrons are gained, oxygen is removed, or hydrogen is added during a reaction by a molecule, atom, or ion.
Example: Zn (s) + 2 H+ (aq) → Zn2+ (aq) + H2 (g)
Q15. Identify the species being oxidized and reduced in the following reaction.
3 Hg2+ + Fe (s) → 3 Hg2 + 2 Fe3+
Answer: Here, the oxidation state of Hg changes from +2 in Hg2+ to 0 in Hg2. Hence it is reduced. And the oxidation state of Fe changes from 0 in Fe to + 3 in Fe3+. Hence it is oxidised.
Practise Questions on Oxidation and Reduction
Q1. When K2Cr2O7 is mixed with H2SO4 and thoroughly shaken with H2O2 in the presence of ether, then a floated blue-colored complex X is formed. What is the change in oxidation state and the percentage of Cr in the complex X?
Q2. Consider a titration of potassium dichromate solution with acidified Mohr’s salt solution using diphenylamine as an indicator. What number of moles of Mohr’s salt is required per mole of dichromate?
Q3. Differentiate between oxidation and reduction.
Q4. Differentiate between oxidation number and oxidation state.
Q5. How do we find the oxidation number of an element?
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