First, coarse salt purification
1. On the scales, weigh 8g coarse salt into a small beaker, add 30ml of distilled water, stir with a glass rod and heated to dissolve. The solution to boiling under agitation was added dropwise 1mol · dm-3BaCl2 solution to precipitate completely (about 2ml), heating was continued so easy to grow BaSO4 particles precipitation and filtration. In order to test whether the precipitate completely, you can remove the beaker from asbestos medium until precipitation sedimentation, add 1-2 drops of BaCl2 supernatant solution was to observe whether there is cloudiness in the supernatant, if no turbidity, indicating SO42 - has completely precipitated. If you still clouding, we need to 71/92 BaCl2 solution until the supernatant after adding one drop of BaCl2, no longer produces clouding up. After precipitation was complete, heating was continued for five minutes, to precipitate particles grow and easy sedimentation, filtration ordinary funnel.
2. Add 1ml2mol · dm-3NaOH and 3ml 1mol · dm-3Na2CO3 solution filtrate heated to boiling. After precipitation sedimentation, the supernatant was dropped in 1mol · dm-3Na2CO3 solution to precipitate no longer so far, with ordinary filtration funnel.
3. Also in the filtrate was added dropwise 2mol · dm-3HCl, with a glass rod and the filtrate was pH paper test, up until the solution was slightly acidic (pH≈6).
4. The solution was poured into an evaporating dish, heat over low heat evaporation, concentrated to a thick gruel-like solution so far, but must not be the solution was evaporated to dryness.
5. After cooling, filtered with a Buchner funnel, try to crystallize drained. The crystals were transferred to an evaporating dish, asbestos medium low heat heating.
6. weighed out the quality of products, and calculate the percentage yield.
Second, the product purity test: Take a small amount (approximately 1g) salt before purification and after purification. Respectively, 5ml dissolved in distilled water, and then filled in each of three test tubes, consisting of three groups, the control test their purity.
1.SO42- test: in the first group of the solution were added 2 drops of 1mol · dm-3BaCl2 solution compared sedimentation resulting in purified salt solution should be no precipitate.
2.Ca2 + test: In the second set of solutions, each 2 drops of 0.5mol · dm-3 ammonium oxalate (NH4) 2C2O4 solution, purified salt solution should be no white precipitate insoluble calcium oxalate CaC2O4.
3.Mg2 + test: In the third set of solutions, each adding 2-3 drops of 1mol · dm-3NaOH solution, and the solution was made alkaline (with a pH paper test) and then adding 2-3 drops of each "magnesium reagent" in purified salt solution should be no sky-blue precipitate.
Magnesium reagent is an organic dye which is yellow in an acidic solution, red or purple in alkaline solution, but was Mg (OH) 2 precipitation after adsorption, the sky was blue, it can be used to verify the presence of Mg2 + .