13. In the balanced chemical equation, c Mno4\" (ag which takes place in acidic

Question

13. In the balanced chemical equation, c Mno4" (ag which takes place in acidic aqueous solution, the ratio of coefficients ba to 3 significant figures is (a) 2.50 (b) 1.60 (c) 2.00 (d) 8.00 (e) 3.200 14. Based upon the standard reduction potentials below, which of the following statements are correct? E 2.92 V K (ag) K(s) t e Als (ag) t 3e Al(s) 1.66 V Cr (ag) 3e E -0.73 V Cr(s) Ag (ag) EG 0.80 V Ag(s) t e Aus (ag) 3e Au(s) +1.50 V (0 Ag is a better reducing agent than Cr (i) Al is a better reducing agent than Cr. (iii) Au is a better oxidizing agent than K Civ) Kwis a better oxidizing agent than Ag (a)iand iii (b) i and iv (c) iii and iv (d) ii and iv (e) ii and iii

Explanation / Answer

13.

MnO4- + 8H+ + 5e = Mn2+   + 4H2O           |x2|

Pb2+ + 2e = Pb4+                                              |x5|

5Pb2+ + 16H+ 2MnO4-    == >5Pb4+ + 2Mn2+   + 8H2O

16/5 = 3.2

14.

In the Standard Reduction Potentials Table:

-the strength of the oxidising agents increases if the potential value is more positive (same sense)

-the strength of the reducing agents decreases if the potential is more negative (opposite sense)

In the proposed series:

-K is the best/strongest reducing agent (look to the reduced form of the half cells)

-Au3+ is the best/strongest oxidising agent (look to the oxidised form of the half cells)

By applying these rules:

i.false . The half cell of Cr has a more negative potential, then Cr is stronger than Ag as reducting agent.

ii.True.   -1.66V is more negative than -0.73V

iii.True.   Au3+ is in the half cell with the highest (positive) potential.

iv.False. The half cell of K+ has a much lower potential.

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