Because barium chloride, sodium hydroxide and sodium carbonate are added to crude salt, the filtrate is filtered to obtain a mixture of sodium chloride, sodium hydroxide and sodium carbonate, hydrochloric acid is added to remove excess sodium hydroxide and sodium carbonate, and then sodium chloride crystals are obtained by evaporation and excess hydrochloric acid solution is removed, because the solute in hydrochloric acid solution is hydrogen chloride gas.

Removal method:

Dissolution: ① Take a proper amount of crude salt (about 3 ~ 4 g) from the medicine spoon in a beaker (no spillage, wipe the medicine spoon after use), put the bottle stopper upside down, cover the bottle stopper after taking it, put it back in its original place, and label it to the operator. (2) pour about 10 mL of water into the beaker (the label is directed to the palm of your hand, and there is no dripping, and the liquid quantity error is not big), put the bottle stopper upside down, take it out, cover the bottle stopper, put it back in its original place, and label it to the operator; Stir with a glass rod (don't make a continuous collision sound), rinse the glass rod and put it back.

Filtration: ① Making a filter: Fold a round filter paper twice, open it in layers one and three, put it into the funnel, press your fingers on the three layers of filter paper, use a rubber dropper to absorb water and moisten the filter paper, so that the filter paper is close to the inner wall of the funnel, lightly press the filter paper with a glass rod to drive out bubbles, and put the made filter on the iron ring of the iron stand.

(2) filtration: the end of the glass rod is lightly leaned against the third layer of the filter paper, the longer part of the nozzle at the lower end of the funnel is close to the inner wall of the beaker, and the beaker mouth is close to the glass rod, so that the liquid flows into the filter along the glass rod, and the liquid level is lower than the edge of the filter paper. Filter to get about 1 mL filtrate, put the residue in the filter into the dirt cup, rinse the glass rod and put it back.

Evaporation: take part of the filtrate (0.5 ~1ml is enough), pour it into an evaporating dish, put it on the iron ring of the iron frame, preheat it first, and then heat it with the external flame of alcohol lamp. Stir the evaporated solution continuously with a glass rod. When more solids appear in the evaporating dish, stop heating, turn off the alcohol lamp, move the evaporating dish to the asbestos net with crucible pliers for cooling, rinse the glass rod and put it back.