A few words about chemistry testing in junior high school will help you understand

In order to accurately determine that the precipitate generated is barium sulfate, the factors that cause silver chloride to form precipitate must be removed first--- so hydrochloric acid is added to check whether there are silver ions, ag+cl-agcl (precipitation).

Nitric acid is added to avoid the effects of other precipitations. CaSO4 (poorly soluble) + HNO3 - Ca(NO3)2 + H2SO4

and caCO3+HNO3--CANO3+HCO3

Barium chloride is then added to determine the presence of sulfate ions in the solution. BA+SO4--BASO4 (precipitate).

The precipitation of CaCO3 in water (2) excludes it CaCO3+Hno3--Ca(NO3)2+H2CO3 and silver ions can be determined to be - just the reaction of chloride ions with silver ions!

1) When testing whether the solution contains SO42-, the interference of dilute hydrochloric acid ag should be added first, and then the BACL2 solution should be added or the dilute nitric acid should be added first, and then the BA(NO3)2 solution should be added.

If there are silver ions that will generate silver chloride precipitate, adding hydrochloric acid can eliminate this interference if there is no precipitation generation, first add dilute nitric acid to exclude barium sulfite precipitation, if there is SO32- added acid, it will react 2) When testing whether the solution contains Cl-, dilute hydrochloric acid should be added to eliminate the interference of CO32-, and then add Agno3 solution. "

Dilute hydrochloric acid was added to eliminate the interference of CO32-, and then Agno3 solution was added. "This practice is not right, the addition of hydrochloric acid introduces chloride ions, and the addition of silver nitrate has a white precipitate, whether it is the original or produced by adding hydrochloric acid, it is impossible to judge. Nitric acid should be applied.

1.If there are silver ions that will form a silver chloride precipitate, the addition of hydrochloric acid can rule out this interference if no precipitate is formed.

Dilute nitric acid is added first to exclude barium sulfite precipitation, and if there is SO32- added acid, it will react away.

2.Hydrochloric acid is added to exclude the interference of silver-white precipitate of carbonate.

If there is CO32- it will react with acid.

1.Dilute nitric acid is added first, and then BA(NO3)2 solution is added, because Ag2SO4 is slightly soluble in solution, and will soon decompose into Ag2O white precipitate.

CO32 = CO2 + H2O, excluding CO32- interference, if added later, AG2CO3 is generated, white, and interference.

Simple. To test for sulfate ions, barium chloride is added directly, and the resulting white precipitate may be silver chloride.

ag+ +cl- =agcl

Silver carbonate is also precipitated.

1) Colorless transparent solution, no copper chloride, potassium carbonate and magnesium chloride at least one.

2) No magnesium chloride.

3) Add barium nitrate. There is potassium carbonate and no potassium sulfate. k2co3+ba(no3)2=2kno3+baco3↓，baco3+2hno3==ba(no3)2+h2o+co2↑

There is no drawback: copper chloride, magnesium chloride, potassium sulfate.

There must be: potassium carbonate.

There may be: potassium chloride.

Add nitric acidified silver nitrate solution to the obtained solution (1), if the wild fruit produces a white precipitate, it means that there is potassium chloride, otherwise, there is no potassium chloride.

Colorless, there must be no copper chloride, and the copper ions are blue.

There is no obvious phenomenon when sodium hydroxide is added, indicating that there is no magnesium chloride.

3 of the title is wrong, quietly pure will not be to add barium sulfate but to add barium nitrate, after filtration precipitation should also be dilute nitric acid, after the title is modified, it should be explained that there is a precipitation dissolved in nitric acid, there must be potassium carbonate in the powder, no potassium sulfate.

Therefore, there must be none: copper chloride, magnesium chloride, potassium sulfate.

There must be: potassium carbonate.

There may be: potassium chloride.

The way to verify potassium chloride is to take a little solution of (1), add excess barium nitrate precipitate to completely start the chain, take a small amount of clear liquid and drop it into silver nitrate, and call if there is a precipitation to indicate that there is potassium chloride.

Or go to a little 1 solution, add excess nitric acid, drop in silver nitrate, and there is a precipitate to produce potassium chloride.

There is a problem with your problem "(3) Take a little of the solution obtained by (1) and add an appropriate amount of barium sulfate to appear white precipitate", barium sulfate imitation itself is a precipitation, and it is sulfuric acid that is not prepared for a slippery posture.

Preliminary judgment. The original powder.

There must be: copper chloride, magnesium chloride, potassium sulfate There must be: potassium carbonate

There may be: potassium chloride.

Case-by-case analysis:

Identification of substances.

Hydrogen, oxygen, carbon dioxide, carbon monoxide, methane Properties of each gas:

Hydrogen is flammable, and the only product of combustion is water; Oxygen can rekindle the sparkled sticks and make the burning sticks burn more vigorously.

CO is flammable, the product of combustion is only carbon dioxide, methane is flammable, and the product of combustion is both water and carbon dioxide.

Carbon dioxide extinguishes the burning sticks; It can make the clarified lime water turbid.

Steps to identify the five gases:

Use burning sticks of wood first: to make the burning sticks burn more vigorously is oxygen; It is carbon dioxide to extinguish the burning sticks;

The gases that can be burned are hydrogen, methane, carbon monoxide.

The second step is to test the products of combustion of flammable gases hydrogen, methane and carbon monoxide: cover the flame with a dry beaker, hydrogen and methane are not generated, and carbon monoxide is generated without anhydrous; The gas produced after combustion passes through the clarified lime water, which can make the lime water turbid, methane and carbon monoxide.

Acid (identification H) method 1: add purple litmus test solution to turn red is the acid solution;

Method. 2. Add active metals such as Mg, Fe, and Zn to release hydrogen.

Alkali solution (identification OH) method 1: add purple litmus test solution to turn blue, add colorless phenolphthalein test solution to turn red is alkali.

Method 2: Add iron sulfate solution to generate reddish-brown precipitate; The addition of copper sulfate solution with blue precipitate is alkali.

Note: The above methods can only identify soluble bases (potassium hydroxide, calcium hydroxide, sodium hydroxide, barium hydroxide, and ammonia).

Method of identifying carbonate: add hydrochloric acid, there is a colorless gas that can make the clarified lime water turbid.

CO3 2) reaction principle: carbonate acid salt H2 o CO2

Identification of sulfuric acid and sulfate: add barium chloride (or barium nitrate) solution dropwise to the solution, and then add dilute nitric acid, there is insoluble SO4 2) in the white precipitate of dilute nitric acid BASO4 generated.

Reaction principle: sulfuric acid or sulfate BaCl2 (or Ba(NO3)2, Ba(OH)2) BaSO4

Identification of hydrochloric acid and chloride (chloride ion, Cl).

Add silver nitrate solution and dilute nitric acid dropwise to the solution, and there is a white precipitate AGCL that is insoluble in dilute nitric acid

Reaction principle: MCLx XAGNO3 m(NO3)X XAGCL

Copper salts: copper sulfate, copper chloride, copper nitrate, their solutions are blue.

It undergoes a displacement reaction with the metal elements in front of the copper, and a red metal copper is formed.

fe ＋ cuso4 ＝feso4 ＋ cu zn＋ cucl2 ＝zncl2 ＋ cu

It reacts with the alkali solution to form a blue precipitate Cu(OH)2 CuSO4 2NaOH Cu(OH)2 Na2 SO4

Iron salts: ferric sulfate, ferric chloride, ferric nitrate, their solutions are yellow and react with alkali solution to form reddish-brown precipitate Fe(OH)3

fe2 （so4 ）3 ＋6naoh ＝2fe(oh)3 ↓＋3na2 so4

Ideas:1Smell and look.

2.Acid-base grouping.

3.Break them one by one.

The information of "Identification and Identification of Chemical Substances in Junior High School" has been uploaded, with methods and topic explanations; Please check it in time, and if it's good, add 50 points!