Chem1612 2014-N-12 Worksheet With Answers - The University Of Sydney - 2014 Page 3

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CHEM1612
2014-N-13
November 2014
2+
What is [Cd
] when E
reaches 0.015 V?
cell
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)(������  ��)
��+
[����
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E
= (0.04 V) –
= +0.015 V
cell
��+
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(��  ×  ����������  ��  ������
)
[����
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so:
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[����
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= 7.0
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2+
If the change from the initial concentrations is x, [Cd
(aq)] = (0.200 – x) M and
2+
[Fe
(aq)] = (0.800 + x) M:
��.������  –  ��
= 7.0
x = -0.075 M
��.������!��
2+
So that [Cd
(aq)] = (0.200 - 0.075) M = 0.125 M.
Answer: 0.125 M
What are the equilibrium concentrations of both ions?
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Using E° =
lnK = 0.04 V gives K = 22.5
����
so:
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[����
���� ]
= 22.5
��!
[����
���� ]
2+
If the change from the initial concentrations is x, [Cd
(aq)] = (0.200 – x) M and
2+
[Fe
(aq)] = (0.800 + x) M:
��.������  –  ��
= 22.5
x = 0.158 M
��.������!��
2+
2+
So that [Cd
(aq)] = (0.200 – 0.158) M = 0.042 M and [Fe
(aq)] = (0.800 + 0.158)
M = 0.958 M
2+
2+
[Cd
] = 0.042 M
[Fe
] = 0.958 M

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