1.Weigh the remaining crude salt on a balance and calculate approximately how many grams of crude salt are dissolved in 10 ml of water.
2. Add excess BaCl2 (to remove sulfate ions) BaCl2+Na2SO4==BaSO4↓+2NaCl
3. Add excess NaOH (to remove magnesium ions) MgCl2+2NaOH==Mg(OH)2↓+2NaCl
4. Add excess Na2CO3 (to remove calcium and Barium ions in BaCl2) Na2CO3+CaCl2==CaCO3↓+2NaCl
5. Na2CO3+BaCl2==BaCO3↓+2NaCl
6 Filter.
7. Evaporate and crystallize.
Apparatus for purification of crude salt:
Pallet balance (with weights), measuring cylinder, beaker, glass rod, medicine spoon, funnel, filter paper, iron stand (with iron ring), evaporating dish, alcohol lamp, crucible tongs, rubber-tipped burette, mortar and pestle, matches, a number of the same small pieces of paper.
Precautions for the purification of crude salt:
Fold the filter paper with a glass rod dipped in water to moisten the inner wall of the funnel and make the filter paper lower than the upper edge of the funnel mouth, the solution level is lower than the filter paper along the mouth of the beaker to pour the liquid to be close to the glass rod, the end of the glass rod is close to the side of the three layers of filter paper, the end of the funnel is close to the inside of the beaker of filtration solution. Pour the liquid slowly, and when there is no water in the filter paper, carefully observe what remains on the filter paper and the color of the filtrate. If the filtrate is still cloudy, it should be filtered again.
If the filtrate is still cloudy after two filtrations, the device should be checked and the cause analyzed. For example, the filter paper is torn, the liquid level in the funnel is higher than the edge of the filter paper during filtration, and the apparatus is not clean. After finding out the reason, to reopen the operation.
When filtering, pay attention to one stick, two low and three lean.
①"A stick" refers to the angle of folding the filter paper to match the funnel wall caliber, so that the wet filter paper close to the funnel wall without bubbles, because if there are bubbles will affect the filtration speed.
② "two low" refers to the edge of the filter paper to be slightly lower than the edge of the funnel, the second is the entire filtration process, but also always note that the liquid surface of the filtrate is lower than the edge of the filter paper. This can prevent impurities unfiltered and flow directly into the beaker, so that the unfiltered liquid and filtrate mixed together, and make the filtrate turbid, did not achieve the purpose of filtration.
③ "three against" one means that the liquid to be filtered when poured into the funnel, beaker beakers of liquid to be filtered beaker mouth to lean on the tilt of the glass rod (glass rod diversion), to prevent splashing and liquid to be filtered to break through the filter paper; the second refers to the lower end of the glass rod should be gently leaning against the three layers of filter paper in order to prevent breaking the filter paper (three layers of filter paper). One side is thicker than the other side of a layer of filter paper, three layers of filter paper side is not easy to break); Third, the neck of the funnel should be close to the receiver of filtrate acceptor wall, in order to prevent the liquid from splashing out.