1, first the crude salt dissolved in water, and then filtered (pay attention to a paste two low three rely);

2, and then add an excess of BaCl? solution, remove Na?SO4: BaCl? + Na?SO? = = = BaSO? ↓ + 2NaCl

3, and then add an excess of NaOH solution, remove MgCl?: MgCl? + 2NaOH. 2NaOH==Mg(OH)? ↓ + 2NaCl

4, and then add an excess of Na?CO? solution to remove CaCl? and BaCl? (two reaction equations): Na?CO? + CaCl? = = CaCO? ↓ + 2NaCl; Na?CO? + BaCl? = = BaCO? ↓ + 2NaCl

5, the last drop of hydrochloric acid to the precise no longer produce gas, remove NaOH and Na?CO? (you can use PH paper to test the pH, there are also two reaction equations): HCl + NaOH = = NaCl + H?O; 2HCl + Na?CO? = = 2NaCl + H?O + CO?↑

6, evaporation of the solution, the precipitation of NaCl crystals.

Crude salt contains insoluble impurities such as sediment, and soluble impurities such as Ca2+, Mg2+, SO?2-? etc. Insoluble impurities can be removed by filtration, while soluble impurities such as Ca2+, Mg2+, SO42- can be removed by adding BaCl?, NaOH and Na?CO? solution to produce precipitation, or by adding BaCO? solid and NaOH solution. The water is then evaporated to obtain a purer refined salt.

Expanded Information:

. p>Apparatus:

Pharmaceuticals: crude salt, distilled water, BaCl? solution, NaOH solution, Na?CO? solution, hydrochloric acid.

Equipment: tray 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, pestle and pestle, matches, and a number of small pieces of the same paper.

Filtering with one stick, two low, three lean.

①"A stick" refers to the angle of folding the filter paper and funnel wall caliber match, so that the wet filter paper close to the funnel wall without bubbles, because if there are bubbles will affect the filtration rate.

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 receiving the inner wall of the acceptor, in order to prevent the liquid from splashing out.

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