Everyone, look at my coarse salt purification, right? Am I confused by the teacher?

The second step is best to add NaOH because magnesium carbonate is slightly soluble, and sodium carbonate may not precipitate completely. There is also no sodium sulfate, because I don't know when the reaction will be completed, it is very likely to introduce new impurities sulfate, and sodium carbonate can go out of barium chloride, so the correct step is to add sodium hydroxide to the point that it can no longer precipitate, and then add sodium carbonate to the point that it can no longer precipitate, and then the sodium carbonate will be excessive, and then the addition of hydrochloric acid can react the sodium carbonate, and then the hydrochloric acid can be heated and volatilized. And the hydrochloric acid in sodium chloride is not considered an impurity.

Remember, sodium sulfate should never be added.

First of all, if you follow your steps, the coarse salt will contain BA ions, so the third step should be advanced to the first step, and the first two steps should be moved to the back, of course, the added solution must be excessive, to ensure that the impurity ions are completely precipitated. As for the final addition of dilute hydrochloric acid (to pH 7), it is to neutralize the excess Na2CO3 added before it, so that the carbonate ions in the solution are removed.

If you add it in the wrong order, take the last one you add will introduce barium ions, because you can't control how much barium chloride you add, you should add bacl2 firstThen NaOH and finally Na2CO3, then add hydrochloric acid. To overdose.

You see, he won't introduce. Moreover, all the impurities will be removed, and finally hydrochloric acid will be added for neutralization.

No new ions are introduced because they are precipitated. Hydrochloric acid, I think it's assuming that the first two are added in excess, and I don't understand the third addition, so I suggest that the landlord ask the teacher to tell us.

There are four steps in total: dissolution, filtration, evaporation, and weighing.

Dissolution Experimental phenomenon: coarse salt solids are (gray) colored. The resulting liquid when added to water is (turbid). The remaining coarse salt is ()g

Conclusion: Coarse salt contains (sediment) and other impurities. Dissolve about 10 ml of coarse salt () g in water

Filtration Experimental Phenomenon: The filtrate is a (clear) liquid of (none) color, and the residue on the filter paper is (black).

Conclusion: The main component of the filtrate is sodium chloride solution.

The coarse salt (sediment) is insoluble in water and is left on the filter paper to be separated. Filtration can remove coarse brine (sediment).

Evaporation Experimental phenomenon: With heating, the evaporation dish.

the amount of medium fluid (decreased); When evaporation reaches a certain level, there is (solid) precipitation from the bottom of the evaporation dish. The solid obtained by evaporation is (white) colored.

Conclusion: If there is splashing of liquid or solid during the heating process, the cause is (uneven heating).The main component of the solid obtained is (sodium chloride).

Weighing Experimental phenomenon: The solid mass is () g

Conclusion: The yield of refined salt is ()%.

Experimental data is required for the unfilled part.

The purification of coarse salt is as follows:Purification of coarse salt means that salt is added.

The impurities contained in it are extracted to produce pure salt. The main reason is that coarse salt contains insoluble impurities such as sediment, mud, stupid mountains, and soluble impurities such as Ca, Mg, SO4, etc.

Throughout this process, the steps of crude salt purification are roughly through dissolution (preliminary separation of insoluble matter from table salt), filtration (complete removal of insoluble matter), evaporation (salt is separated from the solution to obtain salt) to obtain refined salt.

Phenomena in the purification process:Dissolve: The coarse salt solid is gray, and the liquid obtained when added to water is turbid.

Filtration: The filtrate is a colorless transparent liquid, and the residue on the filter paper is black.

Evaporation: With heating, evaporate the dish.

the amount of medium fluid (decreased); When evaporation reaches a certain level, there is (solid) precipitation from the bottom of the evaporation dish. The solid obtained by evaporation is (white) colored.

Insoluble impurities can be removed by filtration, Ca2+, Mg2+, SO42- in soluble impurities can be removed by adding BaCl2, NaOH and Na2CO3 solutions to generate precipitates, and BaCO3 solids and NaOH solutions can also be added. The water is then evaporated to obtain purer refined salts.

Purpose of the experiment. 1.Master the operation skills of dissolution, filtration, evaporation and other experiments.

2.Understand the chemistry of filtration to separate mixtures.

3.Experience the principle of filtration and its application in social practice such as life and production.

4.Refined salt is prepared.

Filtration considerations.

After folding the filter paper, moisten it with a glass rod dipped in water to make it close to the inner wall of the funnel and make the upper edge of the filter paper lower than the mouth of the funnel, the liquid level of the solution is lower than the upper edge of the filter paper, the mouth of the beaker for pouring the liquid should be close to the glass rod, the end of the glass rod is close to the side with three layers of filter paper, and the end of the funnel is close to the inner wall of the beaker containing the filtrate.

Pour the liquid slowly, and when there is no water in the filter paper, carefully observe the residue on the filter paper and the color of the filtrate. When the filtrate is still cloudy, it should be filtered again.

If the filtrate is still cloudy after two filtrations, the device should be inspected and the cause analyzed. For example, the filter paper is damaged, the liquid level in the funnel is higher than the edge of the filter paper during filtration, the instrument is not clean, etc. Once you've figured out the cause, it's time to do it again.

Coarse salt purification:

First, the coarse salt is dissolved in water, then filtered (note that one stick, two low, and three leaning), and then add excess BaCl2 solution to remove Na2SO4: BACL2+Na2SO4==BaSO4 +2NaCl

Then add excess NaOH solution and remove MgCl2: MgCl2+2NaOH ==Mg(OH)2+2NaCl

Then add excess Na2CO3 solution and remove CaCl2 and BaCl2 (two reaction equations): Na2CO3 + CaCl2==CaCO3 +2NaCl Na2CO3 + BaCl2==BaCO3 +2NaCl

Finally, an appropriate amount of hydrochloric acid is added dropwise until it no longer produces gas, and NaOH and Na2CO3 are removed (pH test paper can be used to detect pH level, and there are also two reaction equations): HCl+NaOH==NaCl+H2O

2hcl+na2co3==2nacl+h2o+co2↑

The solution is evaporated and NaCl crystals are precipitated.

Method of coarse salt purification: imitation.

1. Dissolve: Weigh about 4g of coarse salt and add it to a beaker containing about 12ml of water, stir with a glass rod while adding until the coarse salt is no longer dissolved, the solid salt gradually dissolves and decreases, and the salt water is slightly turbid.

2. Filtration: pour the liquid in the beaker into the filter along the glass rod, the liquid level in the filter can not exceed the edge of the filter paper, if the filtrate is turbid, filter it again, the insoluble matter remains on the filter paper, and the liquid seeps into the filter paper and flows into another beaker along the funnel neck.

3. Evaporation: Pour the filtrate into the evaporation dish, then heat it with an alcohol lamp, and constantly stir the solution with a glass rod at the same time, and stop heating when there are more solids. Moisture dust or evaporation, gradually precipitating solids.

The purity is small: the amount of water poured is insufficient when dissolved, and the sodium chloride is only partially dissolved; Liquid spills when dissolved; Failure to drain with glass rods during filtration leads to liquid spillage; When filtering, the beaker is removed without waiting for all the filtrate to flow into the beaker; Heating stops when evaporation dries; When evaporating, the glass rod is not stirred, and the local overheating causes the droplets to splash.

The purity is large: when weighing the quality of coarse salt, "left code right thing"; When dissolving, salt water is used instead of distilled water; During filtration, the filter paper leaked, and some of the sediment entered the beaker.

Insoluble impurities can be removed by filtration, Ca2+, Mg2+, SO42- in soluble impurities can be removed by adding BaCl2, NaOH and Na2CO3 solutions to generate precipitates, and BaCO3 solids and NaOH solutions can also be added to remove them. The water is then evaporated to obtain purer refined salts.

Purpose of the experiment. 1.Master the operation skills of dissolution, filtration, evaporation and other experiments.

2.Understand the chemistry of filtration to separate mixtures.

3.Experience the principle of filtration and its application in social practice such as life and production.

4.Refined salt is prepared.