In chemistry, what to do about the removal of impurities

Abide by the Four Principles:

Do not introduce new impurities, do not reduce the substances to be purified, the reaction should be simple, and the substances to be purified should be easy to restore to the original state.

For impurities, first consider whether the reaction between the impurities and the added substances will cause interference of other substances, or whether the added substances will cause new impurities to interfere, and then how to greatly eliminate the impurities, such as filtration, distillation, and separation of impurities from the substance.

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Problem description: The following substances contain a small amount of impurities, please fill in the appropriate reagent on the horizontal line to remove the impurities.

Substances of impurities should be added to the reagent (or heated).

1) FeCl3 solution (FeCl2).

2) FeCl2 solution (FeCl3, CuCl2) 3) FeSo4 solution (CuSo4).

4)fe2o3 (al2o3) _

5)fe2o3 (fe(oh)3) _

6) Fe(OH)3 (Al(OH)3) Note: Only reagent needs to be filled...

Analysis: (1) FeCl3 solution (FeCl2) —Cl2 (2) FeCl2 solution (FeCl3, CuCl2) —Fe, and then filtered.

3) Feso4 solution (CuSO4) —Fe(4)Fe2O3 (Al2O3) —NaOH, and then filtered.

5) Fe2O3 (Fe(OH)3) — Heating.

6) Fe(OH)3 (Al(OH)3) – NaOH, filtration.

The added reagent only reacts with impurities and not with the original.

No new impurities can be introduced after the reaction.

Return to the original state after the reaction.

The operation method is simple and easy.

Removal of impurities: 1 to see whether the agent to remove impurities reacts with impurities, 2 the selected agent does not react with other substances (some except, such as magnesium chloride and aluminum chloride, such as aluminum chloride (sodium hydroxide, both must react with it, but finally in the addition of hydrochloric acid, magnesium hydroxide can be turned into magnesium chloride). 3. Flexible selection of methods (physical methods can also be used: magnets, iron removal, etc.).

Preferential physical methods, some are magnetic and can be sucked out, some are insoluble, but dissolved and filtered...The chemical method is through chemical reactions....In short, in the simplest and most operable way!

The commonly used chemical impurity removal methods are as follows:

1. Precipitation method: the impurities in the mixture are reacted with appropriate reagents to generate precipitate and removed by filtration. For example, sodium chloride plus an appropriate amount of calcium chloride and then filtration can remove impurities.

2. Gas method: the impurities in the mixture are reacted with appropriate reagents to become gas and removed. For example, sodium chloride and sufficient hydrochloric acid can remove impurities.

3. Substitution method: the impurities in the mixture and the appropriate amount of reagent are removed by substitution reaction. Such as:

Zinc sulfate solid contains a small amount of copper sulfate impurities, after the mixture is dissolved, an appropriate amount of zinc powder is added, and then filtered to remove the replaced copper, and the copper sulfate solid is obtained by evaporating the filtrate.

4. Absorption method: This method can be used when the impurities in two or more mixed gases are absorbed by a certain solvent or solution, and the gas to be purified cannot be absorbed. For example, when carbon dioxide contains sulfur dioxide, the mixed gas can be passed through a saturated sodium bicarbonate solution.

5. Heating method: The impurities in the mixture are converted into other substances by heating to be removed. Such as:

Calcium oxide contains calcium carbonate, which can be decomposed into calcium oxide and carbon dioxide at high temperature by high-temperature combustion, and carbon dioxide diffuses into the air to remove impurities.

When answering questions such as removing impurities, we should pay attention to three principles; Three essentials; Six commonly used chemical methods. Three principles: do not introduce new impurities; does not reduce the mass of the purified substance; Impurities are easy to separate.

Three essentials: according to the difference in physical properties or chemical properties; determine the method of removing impurities; Select the appropriate reagent. Physical Methods:

1.Filtration method: used to remove soluble and insoluble substances Common insoluble precipitates in water are:

AGCL, PBSO4, BaSO4, most carbonates, hydroxides such as Cu(OH)2, Fe(OH)3, Al(OH)3, and MNO2. (The salts formed by potassium, sodium and ammonium are soluble) Example: KCl (AGCL):

Na2SO4 (BaSO4): NaCl(MNO2): 2

The solubility of most solid substances increases with increasing temperature, and the curve is"Steep ascent type", such as kno3 The solubility of a few solid substances is very little affected by humidity and the curve is"Gently ascending", such as the solubility of NaCl very few solid substances decreases with increasing humidity, and the curve is"Descending type", Ca(OH)2Example: The following mixtures are suitable for crystallization separation by a nano3 、na2co3 b.

nano3 、nacl ( c. naoh 、mg(oh)2 d. nacl 、baso4 3.

Magnet attraction: Separation of magnetic and non-magnetic: Example:

1) Iron powder and sulfur powder, etc.