13) Cadmium was once used in rechargeable batteries, but has largely been discon

Question

13) Cadmium was once used in rechargeable batteries, but has largely been discontinued due to its toxicity. Ethylenediamine (en), NH2C2H&NH2;, is a strong ligand that reacts with cadmium to form the complex ion [Cd(en)3]2+, Kf=1.2 x i012. A 2.00 liter sample of water taken from a landfill has an aqueous cadmium ion concentration of 0.040 M. This sample is treated by adding 1.00 mole of ethylenediamine in attempt to reduce the concentration of cadmium. What is the concentration of Cd2 (aq) in the sample once the solution has reached equilibrium? (10 pty)

Explanation / Answer

The no. of moles of cadmium(II) ion in the landfill = 2 L * 0.04 mol/L = 0.08 mol

The no. of moles ethylenediamine (en) added = 1 mol

Let's say: The no. of moles of [Cd(en)3]2+ formed in the solution at equilibrium = x

i.e. The no. of moles of Cd(II) in the solution at equilibrium = 0.08-x

And the no. of moles of en in the solution at equilibrium = 1 - x/3

According to the definition of formation constat, Kf = [Cd(en)3]2+/[Cd(II)] * [en]3

i.e. 1.2*1012 = x/(0.08-x)(1 - x/3)

i.e. 1.2*1012 = 3x/(0.08-x)(3-x)

i.e. 1.2*1012 = 3x/(0.24-3.08x+x2)

i.e. 4*1011 x2 - 1.232*1012 x + 9.6*1010 = x

i.e. 4*1011 x2 - 1.232*1012 x + 9.6*1010 ~ 0

i.e. 40 x2 - 123.2 x + 9.6 = 0

i.e. x = 0.07999

Therefore, the equilibrium concentration of cadmium(II) in the solution at equilibrium = 0.08-0.07999 = 0.00001 M = 10-5 M

Related Questions

Navigate

• Browse (All)
• Browse 1
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.