5. Which of the following reactions is a redox reaction? (a) K2CrO4 + BaCl2 ? Ba

Question

5. Which of the following reactions is a redox reaction? (a) K2CrO4 + BaCl2 ? BaCrO4 + 2KCl (b) Pb22+ + 2Br- ? 2PbBr (c) Cu + S ? CuS

The answer sheet says just C, but shouldn't it be B and C since Lead seems to be gaining an electron in order to bond with Br (ie it is going from 2+ to just 1+)? Please explain why I am incorrect if I am.

5. Which of the following reactions is a redox reaction? (a) K2CrO4 + BaCl2 BaCro, + 2KCI (b) Pb22+ + 2Br-, 2PbBr (c) Cu + S CuS [A] a only [B] b only C] c only [D] a and c E] b and c

Explanation / Answer

look at the oxidation state of all the species present in bpth side

(a) K2CrO4 + BaCl2 BaCrO4 + 2KCl

reactant side K = +1, Cr = +6 , Ba = 2+ , Cl = -1, product side K = +1, Cr = +6 , Ba = 2+ , Cl = -1, all are same nothing is oxidised and reduced, so it is not redox reaction.

(b) Pb22+ + 2Br- 2PbBr

reactant side Pb = 1+ , Cl = -1, product side Pb = 1+ , Cl = -1, all are same nothing is oxidised and reduced, so it is not redox reaction.

(c) Cu + S CuS

reactant side Cu = 0, S=0 product side Cu = +2, S= -2 so Cu is oxidised and S is reduced, so it is redox reaction.

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