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Oxidising Reagent and Reducing Reagent

Which of the ...

Question

Which of the following statements is/are correct about the reaction?
$H_{2} S O_{4} + C u_{3} P + C r_{2} O_{7}^{2 -} \to C u S O_{4} + H_{3} P O_{4} + 2 C r^{3 +}$

The number of moles of

C r_{2} O_{7}^{2 -}

required to oxidise

6

mol of

C u_{3} P

C u S O_{4}

and

H_{3} P O_{4}

11

mol

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The number of moles of

H_{2} S O_{4}

used in the reaction is

62

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The number of moles of

C r_{2} (S O_{4})_{3}

formed in the reaction is

11

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The number of moles of

K_{2} S O_{4}

formed in the reaction is

11

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Solution

The correct options are
A The number of moles of $C r_{2} O_{7}^{2 -}$ required to oxidise $6$ mol of $C u_{3} P$ to $C u S O_{4}$ and $H_{3} P O_{4}$ is $11$ mol
B The number of moles of $H_{2} S O_{4}$ used in the reaction is $62$
C The number of moles of $C r_{2} (S O_{4})_{3}$ formed in the reaction is $11$
D The number of moles of $K_{2} S O_{4}$ formed in the reaction is $11$
i. In $(+ \times 3 C u_{3} P^{- 3})$ ,
$C u_{3}^{1 +} \to 3 C u^{2 +} + 3 e^{-}$ (oxidation)
$P^{3 -} x = - 3 \to H_{3} P O_{4} 3 + x - 8 = 0 x = 5 + 8 e^{-}$ (oxidation)
___________________________________________
$4 H_{2} O + C u_{3} P \to 3 C u^{2 +} + H_{3} P O_{4} + 11 e^{-} + 5 H^{⨁}$ ......(i)
___________________________________________
Reduction:
$C r_{2} O_{7}^{2 -} + 6 e^{-} + 14 H^{⨁} \to 2 C r^{3 +} + 7 H_{2} O$ ...(ii)
Multiply equation $(i)$ by $6$ and equation (ii) by $11$ , net redox equation is given below:
$6 C u_{3} P 6 m o l + 11 C r_{2} O_{7}^{2 -} 11 m o l + 124 H^{⨁}$
$↓$
$18 C u^{2 +} + 6 H_{3} P O_{4} + 22 C r^{3 +} + 53 H_{2} O$
ii. Number of moles of $H_{2} S O_{4}$ used $= 62 H_{2} S O_{4}$ $(= 124 H^{⨁} = 62 S O_{4}^{2 -})$

Number of moles of $C u S O_{4}$ formed $= 18 C u S O_{4}$ $(= 18 S O_{4}^{2 -})$

Number of moles of $C r_{2} (S O_{4})_{3}$ formed $= 11 C r_{2} (S O_{4})_{3}$ $(= 33 S O_{4}^{2 -})$
Total number of $S O_{4}^{2 -}$ ion in reactant $= 62$
Total number of $S O_{4}^{2 -}$ ion in product $= 18 + 33 = 51$
Rest $11$ mol of $S O_{4}^{2 -}$ ion in the reactant react with $11 / 2$ mol of $K^{⨁}$ ion to give $11$ mol of $K_{2} S O_{4}$ .
Net redox reaction is as follows:
$6 C u_{3} P + 11 K_{2} C r_{2} O_{7} + 62 H_{2} S O_{4} \to 18 C u S O_{4} + 6 H_{3} P O_{4} + 53 H_{2} O + 11 C r_{2} (S O_{4})_{3} + 11 K_{2} S O_{4}$
Hence, options A,B,C & D are correct.

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