Preparation and Analysis of Zinc Dithionite

Weigh out 2 g purest zinc dust into a 100 cm conical flask and add 10 cm equivolume of water and ethanol or 10 cm ethanol. Place in the fiime cupboard and pass a slow stream of sulphur dioxide until the zinc dissolves and crystals of the dithionite forms. Cool and quickly filter the product under suction. Wash with a small volume of ethanol and dry by continued suction. Weigh your product and calculate the % yield. 

Dithionites reduce diammine silver nitrate to silver, which is dissolved in nitric acid and the solution titrated against standardised thiocyanate solution. 

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