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Reduction Reactions

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  • Last Updated : 01 May, 2022

Aldehydes, ketones, and carboxylic acids are carbonyl compounds with a double bond between carbon and oxygen. These organic molecules are crucial in organic chemistry and have numerous industrial applications.

What is a Reduction Reaction?

According to the classical or older understanding, the reduction is a process that involves the addition of hydrogen or any other electropositive element, or the removal of oxygen or any other electronegative element.

Reduction is described as the process by which an atom or ion obtains one or more electrons, according to the electronic notion.

Example of Reduction Reaction

  • The H+ ions, with an oxidation number of +1, are reduced to H2, with an oxidation number of 0, in the reaction:

Zn(s) + 2H+(aq) → Zn2+(aq) + H2(g)

  • The interaction of copper oxide with magnesium to produce copper and magnesium oxide is another basic example:

CuO + Mg → Cu + MgO

  • Iron rusting is a two-step process including oxidation and reduction. Iron is oxidized while oxygen is reduced. While the “oxygen” concept of oxidation and reduction makes it simple to see which species are oxidized and reduced, seeing electrons is more difficult. Rewriting the reaction as an ionic equation is one approach to achieve this. Ionic compounds are copper(II) oxide and magnesium oxide, however, metals are not:

Cu2+ + Mg → Cu + Mg2+

To create copper, the copper ion gains electrons and undergoes reduction. To generate the 2+ cation, magnesium undergoes oxidation by losing electrons. You may also think of it as magnesium contributing electrons to copper(II) ions, reducing them. Magnesium is a natural reducer. Copper(II) ions extract electrons from magnesium to generate magnesium ions in the meanwhile. The oxidizing agent is copper(II) ions.

  • Another example is the reaction that extracts iron from iron ore:

Fe2O3 + 3CO → 2Fe + 3CO2

Carbon monoxide is oxidized (gains oxygen) to generate carbon dioxide, whereas iron oxide is reduced (loses oxygen) to form iron. The oxidizing agent, in this case, is iron(III) oxide, which provides oxygen to another molecule. The reducing agent, carbon monoxide, eliminates oxygen from a chemical species.

Important Reduction reactions 

  • Addition of hydrogen:

N2 + 3H2 → 2NH3         (Reduction of nitrogen)

  • Addition of electropositive element:

Fe + S → FeS       (Reduction of mercuric chloride)

  • Removal of oxygen:

ZnO  + C  → Zn  + CO   (Reduction of zinc oxide)

  • Removal of electronegative element:

@FeCl3 + H2 → 2FeCl2 + 2HCl    (Reduction of ferric chloride)

Reducing Agents

The substance that loses electrons and is thereby oxidized to a higher valency state is called a reducing agent.

Important Reducing Agents

  • All metals, such as Na, Zn, Fe, and Al
  • A few non-metals, such as carbon, hydrogen, sulphur, and phosphorus
  • HCl, HBr, HI, and H2S are examples of hydracids.
  • There aren’t many compounds with an element in the lower oxidation state. FeCl2, FeSo4, SnCl2, and Hg2Cl2 are other examples.
  • NaH, LiH, CaH2 and other metallic hydrides
  • HCOOH is an organic chemical.

In the presence of water, lithium is the most powerful reducing agent, but in the absence of water, Cesium is the most powerful reducing agent. H2O2, SO2, H2SO3, HNO2, NaNO2, and other oxidising and reducing agents are H2O2, SO2, H2SO3, HNO2, and NaNO2.

Sample Questions

Question 1: What is the classical idea of reduction reactions?

Answer

The reduction process of ferric chloride comprises 2FeCl3 + H2 → 2FeCl2 + 2HCl, which is a standard reduction reaction. ZnO + C → Zn + CO is used to remove oxygen. Zinc oxide is reduced in this way. SnCl2 + 2HgCl2 → SnCl4 + Hg2Cl2 is the electropositive element addition. Mercuric chloride is reduced in this way. The formula for hydrogen addition is N2 + 3H → 2NH3.

Question 2: Justify that the following reactions are redox reactions: (3 Marks)

(a) CuO(s) + H2(g) → Cu(s) + H2O(g)

(b) Fe2O3(s) +3CO(g) → 2Fe(s) + 3CO2(g)

(c) 4BCl3(g) +3LiAlH4(s) → 2B2H6(g) + 3LiCl(s) + 3AlCl3(s)

Answer:

(a) CuO(s) + H2(g) → Cu(s) + H2O(g)

Here,CuO is reduced to Cu by removing O, whereas H2O is oxidised by adding O to H2 to generate H2O.

Cu’s oxidation number falls from + 2 in CuO to 0 in Cu, while H’s rises from 0 in H2 to +1 in H2O. CuO is therefore reduced to Cu, whereas H2 is oxidised to H2O. As a result, it’s a redox reaction.

(b) Fe2O3(s) +3CO(g) → 2Fe(s) + 3CO2(g)

The oxidation number of Fe in Fe2O3 reduces from +3 to 0 in this reaction, whereas the oxidation number of C increases from +2 in CO to +4 in CO2 .Oxygen is also taken out of Fe2O3 and added to CO. As a result, Fe2O3 is reduced and CO is oxidised. As a result, we get a redox reaction.

(c) 4BCl3(g) +3LiAlH4(s) → 2B2H6(g) + 3LiCl(s) + 3AlCl3(s)

The oxidation number of B reduces from +3 in BrCl3 to -3 in B2H6, whereas H grows from -1 in LiAlH4 to +1 in B2H6 in this reaction. BCl3 is therefore reduced, whereas LiAlH4 is oxidised. H is also taken out of LiAlH4 and added to BCl3. As a result, BCl3 is reduced and LiAlH4 is oxidised. As a result, it’s a redox reaction.

Each K atom loses an electron to generate K+, but each F2 atom gains two electrons to form two F ions. As a result, K is oxidised and F2 is decreased. As a result, it’s a redox reaction.

Question 3: What is Reduction half equation?

Answer:

Only the reduction portion of a redox reaction is shown in this equation, which is balanced in terms of both atoms and charge. The needed number of electrons are added to the left hand side of the equation to establish charge balance.

Question 4: XNa2HAsO3 +YNaBrO3+ZHCl → NaBr + H3AsO4 + NaCl

Find the values of X, Y, and Z in the above redox reaction respectively :

Answer:

The balanced equation is given below.

3Na2HAsO3 + NaBrO3 + 6HCl → NaBr + 3H3AsO4 + 6NaCl

The value of X, Y and Z are 3, 1 and 6 respectively.

Question 5: How many electrons are involved in the following redox reaction?

Cr2O72- + Fe2+ + C2O42- → Cr3+ + Fe3+ + CO2 (Unbalanced)

Answer:

Any chemical process in which the oxidation number of a molecule, atom, or ion changes by gaining or losing an electron is known as a redox reaction. In the oxidised and reduced process, chromium and iron are involved. In this redox process, there are a total of 6 electrons involved.

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