Ogin × (E) Exam 3 Bonus Question ( x es.edu/d2l/le/content/234458/viewContent/26

Question

Ogin × (E) Exam 3 Bonus Question ( x es.edu/d2l/le/content/234458/viewContent/2610571/View You are working on a project to recycle nickel and cadmium from old nickel-cadmium batteries. The batteries are dissolved in aqueous nitric acid, producing a solution containing primarily Ni Cd, and Fe cations and associated anions (the iron comes from the casing). One idea is to concentrate the solution by evaporation using solar energy, and then add sodium hydroxide to neutralize the acid and cause precipitation of Ni(OH)2, Cd(OH)2, and Fe(OH)s. For simplicity, assume the concentration of each of the cations is 0.100 M before the sodium hydroxide is added. The pH increases as the sodium hydroxide is added. 1) Identify the compound that will precipitate first (you must either show your work, or fully explain your answer), and 2) determine the pH at that point. First compound to precipate:_ Compound K Ni(OH)2 2.8 x 1016 Cd(OH)2 Fe(OH) 6.3 x 10 pH when it precipitates: 1.2 x 10-14 × 10-38 Reflect in ePortfolia Download

Explanation / Answer

First compound to precipitate will be Fe(OH)2 as it has the lowest solubility product. On increasing pH i.e. concentration of OH- ions, as soon as the ionic product ([cation] x [anion]) will reach the solubility product, it will cause Fe(OH)3 to precipitate.

So, [Fe3+] =0.1M

Ksp = [Fe3+] x  [OH-]3

Therefore, [OH-] for precipitation = (Ksp/  [Fe3+])1/3

= (6.3 x 10-38 / 0.1)1/3 = 8.57 x 10-13 M

so, pOH = -log(8.57 x 10-13 ) = 12.07

Therefore pH = pkw -pOH= 14-12.07= 3.93

Related Questions

Navigate

• Browse (All)
• Browse O
• Subjects

---

---

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