Q1(h). Spectrophotometric chromium in a mineral

Answer in brief

Bring chromium into solution, convert it to Cr(VI), and develop the diphenylcarbazide colour for measurement near 540 nm.

Key points

• Obtain a representative sample and dissolve it by a suitable digestion or alkaline oxidative fusion if the mineral is refractory. Quantitatively transfer and dilute.
• For total chromium, oxidise all chromium to Cr(VI), then remove or destroy excess oxidant without reducing the analyte.
• In controlled acidic medium add 1,5-diphenylcarbazide. Redox reaction and complexation produce the red-violet Cr(III)–diphenylcarbazone species.
• Measure near 540 nm against a reagent blank and use standards treated identically.