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Redox Reactions

Multiple Choice Questions

71.

The reaction, 10FeSO₄ + 2KMnO₄ + 8H₂SO₄ → 2MnSO₄ + 5Fe(SO₄)₃ + K₂SO₄ + 8H₂O is an example of reaction of

disproportionation
intermolecular redox
intramolecular redox
None of these

72.
Standard electrode potential data are useful for understanding the suitability of an oxidant in a redox titration. Some half cell reactions and their standard potentials are given below
${MnO}_{4}^{-} (aq) + 8 H^{+} (aq) + 5 e^{-} \to {Mn}^{2 +} (aq) + 4 H_{2} O (l) : E^{°} = 1.51 V {Cr}_{2} O_{7}^{2 -} (aq) + 14 H^{+} + 6 e^{_} \to 2 {Cr}^{3 +} + 7 H_{2} O (l) : E^{°} = 1.38 V {Fe}^{3 +} (aq) + e^{-} \to {Fe}^{2 +} (aq); E^{°} = 0.77 V {Cl}_{2} (g) + 2 e^{-} \to 2 {Cl}^{-} (aq); E^{°} = 1.40 V$
Identify the incorrect statement regarding the quantitative estimation of gaseous Fe(NO₃)₂.

MnO $_{4}^{-}$ can be used in aqueous HCl

Cr₂O $_{7}^{2 -}$ can be used in aqueous HCl

MnO $_{4}^{-}$ can be used in aqueous H₂SO₄

Cr₂O $_{7}^{2 -}$ can be used in aqueous H₂SO₄

MnO $_{4}^{-}$ can be used in aqueous HCl

The reaction between MnO $_{4}^{-}$ and HCl may be represented as follows:

${MnO}_{4}^{-} (aq) + 16 H^{+} + 10 {Cl}^{-} \to 2 {Mn}^{2 +} (aq) + 8 H_{2} O (l) + 5 {Cl}_{2} (g)$

Thus, on the basis of this reaction following electrochemical cell will be represented

PtCl₂(g)(1atm)| Cl^-(aq)|| MnO $_{4}^{-}$ (aq) | Mn²⁺ (aq)

$Since, E_{cell}^{°} = E_{cathode}^{°} - E_{anode}^{°} From given data E_{cell}^{°} = 1.51 - 1.40 = 0.11 V$

E°_cell is positive, hence ΔG° is negative. Thus, above cell reaction is feasible but MnO $_{4}^{-}$ ion can oxidise, Fe²⁺ to Fe³⁺ and Cl^- to Cl₂ aqueous medium alo. Therefore, for quantitative estimation of aqueous Fe(NO₃)₂, it is not a suitable reagents.

73.

Oxidation number of chlorine atom in Ca(OCl)Cl is

-1
+1, -1
0
-1, 0

74.

The $E_{M^{2 +} / M^{2 +}}^{°}$ value for Cr, Mn, Fe and Co are -0.41, +0.77 and +1.97 V respectively. For which one of these metals the change in oxidation state from +2 to +3 is easiest?

75.

The oxidation numbers of phosphorus in Ba(H₂PO₂) and xenon in Na₄XeO₆ respectively are

+3 and +4
+2 and +6
+1 and +8
-1 and -6

76.

Balance the following equation by chossing the correct options:

xKNO₃ + yC₁₂H₂₂O₁₁ → pN₂ + qCO₂ + rH₂O + sK₂CO₃

x y p q r s

36 55 24 24 5 48
x y p q r s

48 5 24 36 55 24
x y p q r s

24 24 55 48 5
x y p q r s

24 48 36 24 5 55