The concentration of copper in the solution is
[tex]5.1 \times 10^{18} \: M.[/tex]
The volume of the solution = 1.00 L
[tex]Moles \: of \:Cu(NO_{3}) _{2} = 2.50 \times 10 {}^{ - 4} [/tex]
[tex]Moles \: of \: Ethylenediamine = 1.20 \times 10.3[/tex]
[tex]k _{f} = 1.00 \times 10^{20} [/tex]
Overall balanced equation of reaction is,
[tex]Cu^{2 + }(aq) \: + 2en \: (aq)→ Cu(en) ^{2 + }_{2}(aq)[/tex]
[tex]Moles \: of \:Cu(NO_{3}) _{2} =0.00025 \: mol[/tex]
Mole ratio for,
[tex]Moles \: of\:Cu(NO_{3}) _{2}: en[/tex]
[tex]2: 1[/tex]
[tex]Moles \: of \: en = 0.000250 \times 2[/tex]
[tex] = 0.00050 \: moles[/tex]
Remained moles of en are= (0.00120-0.000500)
[tex] = 0.000700 \: moles[/tex]
The concentration of copper in the solution is,
[tex]k_{f} = \frac{Cu(en)^{2 + }_{2} }{Cu^{2+}en^{2} }[/tex]
[tex]1.00 \times 10 ^{20} = \frac{0.000250}{(Cu )^{2 +} \times (0.000700)^{2 + } }[/tex]
[tex] = 5.1 \times 10^{18} \: M.[/tex]
Therefore, the concentration of copper in the solution is
[tex]5.1 \times 10^{18} \: M.[/tex]
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