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61.
Show that oxidation cannot occur without reduction.
Or
Show that oxidation and reduction go side by side.

In a chemical reaction, the species which loses electrons is said to be oxidised and the species which gains electrons is said to be reduced. Since there is no net loss or gain of electrons in a chemical reaction, it means that a substance can gain electron only if another substance that can lose electron is also present in the system. Similarly, a substance can lose electrons only if another substance which can gain electrons is also present in the system. This means oxidation can take place only if reduction also takes place simultaneously and vice versa. In other words, oxidation-reduction reactions are electron transfer processes and always occur side by side. Such reactions in which oxidation and reduction take place simultaneously are called oxidation-reduction or simply redox reactions. For example, consider the following reaction:

This reaction consists of two distinct simultaneous processes which take place in such a way that

No. of electrons lost = No. of electrons gained
(i) Oxidation half-reaction:

Here each atom of zinc loses two electrons and thus gets oxidised to Zn²⁺ ions.
(ii) Reduction half-reaction:

Thus, a redox reaction may also be defined as a reaction in which electrons are transferred from one reactant to the other.

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62. In the following reactions:

space space left parenthesis straight i right parenthesis space straight H subscript 2 straight O space plus space 2 FeCl subscript 3 space space space space space rightwards arrow space space space space 2 FeCl subscript 2 space plus space 2 HCl space plus space straight S space space left parenthesis ii right parenthesis space 2 Al space plus space Fe subscript 2 straight O subscript 3 space space rightwards arrow space space space Al subscript 2 straight O subscript 3 space plus space 2 Fe

which is oxidised to what and which is reduced to what? Also, mention the oxidising and reducing agent.

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Short Answer Type

63.

Identify the oxidant and the reductant in the following reactions:
$left parenthesis straight i right parenthesis space Zn left parenthesis straight s right parenthesis space plus space 1 half straight O subscript 2 left parenthesis straight g right parenthesis space space rightwards arrow space space ZnO left parenthesis straight s right parenthesis left parenthesis ii right parenthesis space Zn left parenthesis straight s right parenthesis space plus space 2 straight H to the power of plus left parenthesis aq right parenthesis space space rightwards arrow space space Zn to the power of 2 plus end exponent left parenthesis aq right parenthesis space plus space straight H subscript 2 left parenthesis straight g right parenthesis$

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64. In the reactions given below, identify the species undergoing oxidation and reduction:

left parenthesis straight i right parenthesis space straight H subscript 2 straight S left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis space space rightwards arrow space space space 2 HCl space left parenthesis straight g right parenthesis space plus space space straight S left parenthesis straight s right parenthesis left parenthesis ii right parenthesis space 3 Fe subscript 3 straight O subscript 4 left parenthesis straight s right parenthesis space plus space 8 Al space left parenthesis straight s right parenthesis space rightwards arrow space space space 9 space Fe left parenthesis straight s right parenthesis space plus space 4 Al subscript 2 straight O subscript 3 left parenthesis straight s right parenthesis left parenthesis iii right parenthesis space 2 Na left parenthesis straight s right parenthesis space plus space straight H subscript 2 left parenthesis straight g right parenthesis space rightwards arrow space space 2 NaH left parenthesis straight s right parenthesis

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65. Using Stock notation, represent the following compounds : HAuCl₄, Tl₂O,FeO, Fe₂O₃, CuI, CuO, MnO and MnO₂?

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66.

How will you classify the redox reactions?

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Long Answer Type

67.

What are the changes which take place when a redox reaction is carried in a beaker? Explain with the help of a suitable example.
Or
Explain the redox reaction

$Zn space plus space CuSO subscript 4 space space rightwards arrow space space ZnSO subscript 4 space plus space Cu$
occurring in a beaker.

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68.

What do you mean by redox reactions in aqueous solutions? Give examples.

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Short Answer Type

69.

Write the half reactions for each of the following redox reactions:
$left parenthesis straight a right parenthesis space 2 Fe to the power of 3 plus end exponent left parenthesis aq right parenthesis space plus space 2 straight I to the power of minus left parenthesis aq right parenthesis space space rightwards arrow space space straight I subscript 2 left parenthesis straight s right parenthesis space plus space 2 Fe to the power of 2 plus end exponent left parenthesis aq right parenthesis left parenthesis straight b right parenthesis space Sn to the power of 2 plus end exponent left parenthesis aq right parenthesis space plus space 2 Hg to the power of 2 plus end exponent left parenthesis aq right parenthesis space rightwards arrow space space Sn to the power of 4 plus end exponent left parenthesis aq right parenthesis space plus space 2 straight H to the power of plus left parenthesis aq right parenthesis$

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Long Answer Type

70. In the following reactions:

1. space 2 Na left parenthesis straight s right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis space space space rightwards arrow space space space 2 NaCl left parenthesis straight s right parenthesis 2. space Mg left parenthesis straight s right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis space space rightwards arrow space space MgCl subscript 2 left parenthesis straight s right parenthesis 3. space Zn left parenthesis straight s right parenthesis space plus space 2 straight H to the power of plus left parenthesis aq right parenthesis space space rightwards arrow space space Zn to the power of 2 plus end exponent left parenthesis aq right parenthesis space plus space straight H subscript 2 left parenthesis straight g right parenthesis

Mention:
(i) Which reactant is oxidised? To what?
(ii) Which reactant is an oxidising agent?
(iii) Which reactant is reduced?
(iv) Which reactant is reducing agent?

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