Water-soluble toxic chromium compounds are waste products of electroplating operations, but the chromium can be precipitated as Cr(OH)₃ to remediate the water. How much 1.0 M NaOH solution is needed to remove the chromium from 100 L of a solution that is 0.001 M in Cr³⁺?

Question

Quizplus · Accepted Answer

The chromium is present as Cr^3+ in the solution. The reaction to form Cr(OH)3 is: Cr^3+ + 3OH^- → Cr(OH)3. Each mole of Cr^3+ requires 3 moles of OH^- to precipitate as Cr(OH)3. The solution is 0.001 M in Cr^3+, so 100 L contains 0.1 moles of Cr^3+. Therefore, 0.3 moles of OH^- are needed. Since the NaOH solution is 1.0 M, 0.3 L (or 300 mL) of NaOH is required to provide the necessary OH^- ions.

Water-Soluble Toxic Chromium Compounds Are Waste Products of Electroplating Operations