Dissolve 50 g of sodium bisulfite in 50 mL of water, stir vigorously. Then put the beaker into an ice bath, cool down to 20°C and add 19 g of very fine zinc dust, stir vigorously. Add 10 mL of water and stir vigorously, filter and wash with 10 mL of water twice, don’t allow air to flow through it, sodium dithionite is air sensitive. The impure solution can be used immediately. Then pour the mixture to 75 mL of dry ethanol, put to a freezer for to precipitate the dithionite, filter and wash with 15 mL of ethanol, do not allow much of air to flow through it. Dry in a vacuum desiccator and store under inert gas.
2 NaHSO3 + Zn = Na2S2O4 + Zn(OH)2
The zinc was added over vigorous stirring
Some water was added and the mixture loosened up
Filtration with washing
The crude sodium dithionite solution
Precipitating the sodium dithionite with anhydrous ethanol
Pure sodium dithionite