The best results are obtained by
precipitating from homogeneous solution utilising the homogeneous generation of
chromate ion produced by slow oxidation of chromium (III) by bromate at 90-95
°C in the presence of an acetate buffer.
Use a sample solution containing 0.1-0.2g lead. Neutralise the solution by adding sodium hydroxide until a precipitate just begins to form. Add 10 mL acetate buffer solution [6M in acetic acid and 0.6M in sodium acetate], 10 mL 2.5% chromium nitrate solution, and 10 mL 2% potassium bromate solution. Heat to 90-95 °C. After generation of chromate and precipitation are complete (about 45 minutes) as shown by a clear supernatant liquid, cool, filter through a weighed sintered-glass or porcelain filtering crucible, wash with a little 1 per cent nitric acid, and dry at 120 °C. Weigh as PbCrO4.