Preparation of Hypophosphorous Acid

Preparation of Hypophosphorous Acid. (Perform the experiment in a fume cupboard ) Assemble an apparatus as shown in Fig. 98. Prepare a suspension of 12 g of barium hydroxide in 150 ml of water 

Pass carbon dioxide through the reaction mixture during 15 min (connect a Kipp gas generator to tube 4). Filter the precipitate (what is its composition ) on a Biich-ner funnel and wash it with several portions of hot water (50-60°C). 

Evaporate the filtrate together with the washing water in a porcelain bowl in a water bath up to one-third of the initial volume, again filter the solution through a smooth filter, and once more evaporate it up to the appearance of a crystalline film (he careful, avoid overheating ). Add an equal volume of ethanol to the warm solution. 

Cool the mixture and separate the crystals by filtration. Write the equations of the reactions. 

Treat the unreacted white phosphorus deposit remaining on the walls of the reaction flask with bromine water. 

---

Fig. 197. Evaporation apparatus for the preparation of hypophosphoric acid, a) Drain b) vaporizer (actually five heating tubes instead of the three shown) h) heating medium h) cooling liquid 1) air intake s, ) ground-glass ball and socket joints y) vacuum connection.

---