Question

In: Chemistry

Be sure to answer all parts. In the presence of aqueous ammonia, cobalt(III) forms the complex...

Be sure to answer all parts.

In the presence of aqueous ammonia, cobalt(III) forms the complex ion Co(NH₃)₆³⁺. Determine the molar concentration of free cobalt(III) ion in solution when 0.200 mole of Co(NO₃)₃ is dissolved in a liter of 2.50 M aqueous ammonia.

__ x 10 __ M

Expert Solution

ans)

from above data that

The formation constants are very large. Since K_f is large, assume all the Co^{3+ i}s consumed and converted to complex ion, Co(NH₃)₆³⁺.

We can determine the concentration of Co³⁺ ions produced by the subsequent dissociation of the complex ion.

The formation constant 'K_f' for the complex ion, Co(NH₃)₆³⁺ is 5.0 10³¹

[NH₃] = 2.50 – 6 0.200 = 1.3

Co³⁺+ 6 NH₃Co(NH₃)₆³⁺

0 1.180 200

x +6x -x

x 1.3+ 6x 0.200–x

Since x will be small, 1.3 + 6x ≈ 1.3 and 0.200–x ≈ 0.200

K_f = 5.00 x 10³¹= [Co(NH₃)₆³⁺]/([Co³⁺][NH₃]^₆)

Rearranging the above equation,

[Co³⁺] = [Co(NH₃)₆³⁺]/(NH₃]^₆ Kf) = 0.200 /1.3⁶/5.00 x 10³¹ = 8.29x 10^-34

queen_honey_blossom answered 2 years ago

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