1、 Experiment purpose
1. The purification principle of potassium and sodium chloride was studied through precipitation reaction;
2. Practice the use of platform scale and electric heating jacket;
Master the basic operations of dissolution, decompression filtration, evaporation concentration, crystallization, drying, etc.
2、 Experimental principle
Crude table salt contains insoluble impurities (such as mud and sand) and soluble impurities (mainly Ca 2+ 、Mg 2+ 、K + And SO four 2- ）。 Insoluble impurities can be removed by dissolving and filtering. Soluble impurities can be removed by the following methods, and a slight excess of BaCl is added to the crude salt solution two Solution, SO four 2- Transformed into insoluble BaSO four Precipitation and removal.
Ba 2+ + SO four 2- = BaSO4 ↓
Filter the solution to remove BaSO four Precipitate, then add NaOH and Na two CO three Solution, due to the following reactions:
Mg 2+ + 2OH - = Mg(OH) two ↓
Ca 2+ + CO three 2- = CaCO three ↓
Ba 2+ + CO3 2- = BaCO three ↓
Impurity Mg in salt solution 2+ 、Ca 2+ And precipitation SO four 2- Excess Ba added at 2+ Will be correspondingly transformed into insoluble Mg (OH) two 、 CaCO three 、BaCO three Precipitation is removed by filtration.
