Zinc Oxide

Zinc Oxide USP



Identification A: When strongly heated.it assumes a yellow colour that disappears on cooling.
B : A solution of it in a slight excess of 3 N hydrochloric acid responds to the test of zinc
Alkalinity Mix 1.0 g with 10 ml of hot water, add 2 drops of phenolphthalein TS, and filter:.If a red colour is produced not more than 0.3 ml of 0.1 N hydrochloric acid is require to discharge it.
Loss On Ignition Weigh accurately about 2 g and ignite at 500 C,to constant weight :it loses not more than 1.0 % of its weight.
Carbonate and Colour Of Solution Mix 2.0 gm to 10 ml of water 30 ml of 2 N sulphuric acid, and heat on steam bath with constant stirring: no effervescence occurs and the resulting solution is clear and colourless.
Arsenic Dissolve 2 g in 15 ml of brominated hydrochloric acid AsT and 45 ml of water and remove the excess of bromine with a few drops of stannous chloride solution AsT The resultant solution complies with the limit test for arsenic Appendix 3.9 (6 ppm)
Lead Add 2g to 20 ml water stir well, add 5 ml of glacial acetic acid and warm on a steam bath until solution is effected the addition of 5 drops of potassium chromate TS produces no turbidity or precipate.
Iron and other heavy metals Cooled 5 ml portions of the solution obtained in the test for carbonate and colour of solution yield white precipitates with potassium ferrocyanide TS and with sodium sulphide Ts.
Assay Dissolve 1.5 g of freshly ignited Zinc Oxide accurately weighed, and 2.5 g of ammonium chloride in 50 ml of 1 N sulphuric acid VS with the aid of gentle heat if necessary when solution is complete,add methyl orange TS.and titrate the excess sulphuric acid with 1 N sodium hydroxide Vs each ml of 1 N sulphuric acid equivalent to 40 .69 mg of ZnO.
(Zinc Oxide contents not less than 99.0 % and not more than 100.5 %)