Write the Nernst equation and emf of the following cells at 298 K: (i) Mg(s) | Mg2+(0.001M) || Cu2+(0.0001 M) | Cu(s) (ii) Fe(s) | Fe2+(0.001M) || H+(1M)|H2(g)(1bar) | Pt(s) (iii) Sn(s) | Sn2+(0.050 M) || H+(0.020 M) | H2(g) (1 bar) | Pt(s) (iv) Pt(s) | Br2(l) | Br−(0.010 M) || H+(0.030 M) | H2(g) (1 bar) | Pt(s).
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Answer:
(i) E o =0.34−(−2.37)=2.71 V
E=E 0 − n0.059
log [Cu 2+ ]
[Mg 2+ ]
E=2.71−
2
0.059
log
(0.0001)
0.001
E=2.6805 V
(ii) E
o
=0−(−0.44)=0.44 V
E=E 0 − n0.059
log
[H + ] 2
[Fe 2+ ]
E=0.44−
2
0.059
log
(1)
2
0.001
E=0.5285 V
(iii) E
o
=0−(−0.14)=0.14 V
E=E 0 − n0.059
log
[H + ] 2
[Sn 2+ ]
E=0.14− 20.059
log
(0.020) 2
0.050
E=0.08 V
(iv) E
o
=0−1.08=−1.08 V
E=E
0
−
2
0.059
log
[Br
−
]
2
[H
+
]
2
1
E=−1.08−
2
0.059
log
(0.01)
2
(0.030)
2
1
E=−1.288 V
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