Ask another chemistry question for junior high school students to identify a variety of substances w

1. If a reagent is used, select the characteristic ions to combine into a substance according to the anions and cations of the identified substance.

As in the example above, hydrogen ions can be found from the carbonate ions in sodium carbonate and sulfate ions from barium chloride.

In this way, sulfuric acid is combined. Samples were taken separately, dilute sulfuric acid was added, sodium carbonate appeared with bubbles, and barium chloride was generated by precipitation;

In the two reagents without phenomenon, samples were taken again, and sodium carbonate was added respectively, with hydrochloric acid and sodium chloride without phenomenon.

2. If you don't use reagents for identification, if there is a color, you can use it to test other substances separately, and then use the tested ones to test other substances in turn;

If the solution is colorless, it can only be used in pairs, and it can be identified according to the combination of phenomena.

Mixed in pairs, only white precipitate is BACL2 after mixing;

After mixing, only the gas produced is HCl;

After mixing, there is both gas and precipitate Na2CO3;

NaCl is non-symptomatic after mixing

Identification questions are a type of junior high school chemistry questions, and they do not use reagents to identify, in fact, they do not use other reagents to identify, but only use existing reagents to identify.

This kind of topic has two characteristics, one is that the phenomenon is different, first consider the physical phenomenon, such as color, smell, state, etc., which does not seem to be covered in this topic, and secondly, consider the phenomenon in chemical change, which mainly includes precipitation, gas, color and temperature changes. The characteristic of the two is that they need to be mixed with each other, and it is difficult to see all of them at once just by putting them on the table, so it is necessary to observe the phenomenon by mixing, and then reasonably deduce the substance according to the phenomenon.

This kind of question is generally not suitable for beginners, because it is necessary to connect with the characteristics of many ions, and it is mainly practiced in the second half of the third semester of junior high school.

1. First of all, find out the two reagents that will produce precipitation, namely Na2CO3 and BaCl2 to generate BaCO3 precipitation.

2. The other two reagents are used to react with the above precipitation (BaCO3 precipitation can react with HCl to form CO2, and the phenomenon is to produce bubbles).

HCl is first distinguished

3. After that, HCl is mixed with NaCl, Na2CO3, and BaCl2 respectively, and it is Na2CO3 that produces bubbles

Na2CO3 was then identified

4. After that, BACL2 is judged directly (reason check 1).

5. The last bottle of reagent is NaCl, and no reagent means no other reagents. You can identify them with several substance reactions to be identified.

The last point: If it is an experimental question, you must add the words "sampling separately".

Take a small amount of four drugs dissolved in water, mix them in pairs, and produce Na2CO3 solution with gas and precipitation at the same time, and react with Na2CO3 to form a precipitate of BaCl2 solution, Na2CO3 BaCl2 = 2NaCl BaCO3 (precipitation symbol).

The reaction with Na2CO3 to form a gas is a HCl solution, Na2CO3 2HCl=2NaCl CO2 (gas symbol) H2O

The rest is NaCl solution.

HCl here should refer to hydrochloric acid, 1, mixed in pairs, and the precipitate must be Na2CO3 and BaCl2 after mixing

2. Mixing in pairs, the gas produced after mixing must be Na2CO3 and HCl, therefore, after the mixing of two pairs, there is both gas and precipitation is Na2CO33, then the other that produces gas is HCl, and the other one that produces precipitation is BaCl2

HCl is a gas, do you mean an aqueous solution of several substances mentioned above. If it is an aqueous solution, take some of them from each other and mix them in pairs, which produce bubbles with HCl and Na2CO3, and produce precipitate with Na2CO3 and BACL2. This allows Na2CO3, BaCl2, HCl to be determined.

The one left is NACL.

No reagents means no other reagents. You can identify them with several substance reactions to be identified.

The equations for the reactions of these four substances are all written. There are 16 in total. Only the sodium carbonate is then dropped into other liquids to produce a gas precipitate at the same time.

So push it back: take one reagent and drop it into the other 3. If precipitation is generated and gas is generated.

Then the reagent of choice is sodium carbonate. Then the gas is formed by HClThe precipitated is bacl2

The rest is NACL, which is to write a chemical equation for each of them. Then, according to the peculiarities of the reaction of a substance with other substances, it is pushed backwards backwards.

Take the above liquids from each other for two and two reactions, one of which reacts with two other three liquids, there is a phenomenon when there is a bubble, there is a phenomenon when there is a white precipitate, then this liquid is Na2CO3, and then the known liquid Na2CO3 is used to react with the other three respectively, the bubble is HCl, the precipitate is BaCl2, there is no reaction of NaCl, there is a chemical equation in the book, the method is to reverse according to the characteristics of the reaction phenomenon.

The samples were added separately and mixed in pairs, and there was no phenomenon of NaCl, Na2CO3 with gas and precipitation, HCl with gas, and BaCl2 with precipitation

There are two kinds of phosphate rock powder, gray or brown, the main component is fluorine-apatite, containing 10-35% of total phosphorus (phosphorus pentoxide), of which 3-5% of phosphorus is soluble in weak acid, [phosphate rock powder in junior high school chemistry textbooks is [Ca3(PO4)2] can be absorbed and utilized by crops, and most other crops are difficult to directly absorb and utilize, which is insoluble phosphate fertilizer. After being applied to the soil, it mainly depends on the acidity in the soil, soil microorganisms, and the weak acid secreted by the roots of crops to be transformed, so that it can be absorbed and utilized by crops, and its fertilizer effect is very slow and long-lasting. Once applied, the fertilizer effect can be maintained for several years.

ab is right.

ammonium nitrate white. Soluble in water. Phosphate rock is powdery-gray or brown. Insoluble in water.

bAlcohol has a special smell, and the salt water has white crystals after evaporation.

a. Correct ammonium nitrate white soluble phosphate rock powder off-white partially soluble.

b Correct salt water is odorless and will have solids after evaporation.

B. Salt water and medical alcohol: 1. Smell the odor, 2. Evaporate and crystallize.

Alcohol has a peculiar odor, and salt water has a white solid after evaporation.

It is to choose NaOH dissolved in water and violently exothermic, NaCl dissolved in water is basically not exothermic, and CaCO3 is insoluble in water.

b.NaOH plus phenolphthalein turns red, and then NaCl red does not recede, and then excessive HCl red fades.

There is a precipitate with sodium carbonate, and the precipitate with HCl is dissolved; HCl plus sodium carbonate has gas.

Add hydrochloric acid to dissolve into a blue solution. Charcoal plus hydrochloric acid is insoluble, Fe3O4 plus hydrochloric acid is a yellow-green solution.

A you understand exactly right, no nonsense.

B NaOH, NaCl, HCL three solutions plus phenolphthalein test solution The color is red, white and white The solution that makes phenolphthalein turn red (NaOH) is slowly added to the other two drops of phenolphthalein, which directly turns red is NaCl, and it is HCl that turns red after adding a certain amount.

D Cuo, charcoal, Fe3O4 three powders plus hydrochloric acid one is a blue solution Cuo one is a yellow solution Fe3O4, and the other is a precipitate insoluble.

a. Sodium hydroxide is dissolved in water and exothermic, and calcium carbonate is insoluble in water.

b. First add three solutions with phenolphthalein, sodium hydroxide turns red, add the reddened sodium hydroxide dropwise to the other two solutions, the red disappears hydrochloric acid, and the rest is sodium chloride.

c. Unrealizable.

d. After adding hydrochloric acid, it is carbon that is insoluble, and copper ions in the copper chloride solution generated by copper oxide and hydrochloric acid are blue and can be distinguished.

1。First consider the color and smell (e.g. copper sulphate solution is blue, ammonia has a pungent odor)2. Then the solution resolved in 1 is added to other solutions to see if precipitate or bubbles are generated, so as to judge the composition of other solutions.

3。Repeat in 2 and continuously add the identified solution to the unidentified solution until all parts are identified.

The main thing is to remember the equations of the reactions of different solutions and the characteristics of the products, and then analyze them according to the actual situation. More practice will improve your proficiency.

Those who can see the color look at the color, and then exchange each other, different phenomena are different substances.

First of all, the color was observed, and the first one to be identified was the blue Cu(NO3)2 solution, and the rest was a colorless solution.

Cu(NO3)2 solution was added dropwise to a small remaining solution to produce a blue precipitate which was NaOH solution, so the second identified substance was NaOH solution;

Then the NaOH solution was divided into a little of the remaining three solutions, and the white precipitate produced was the MGSO4 solution, so the third identified substance was the MGSo4 solution;

Then the MgSO4 solution was put into a little of the remaining two solutions, and the white precipitate produced was the BA(NO3)2 solution, and the KNo3 solution was the KNO3 solution without obvious phenomenon

Therefore, the correct order to be identified is:

Therefore, choose B

A No, A can see that the copper sulfate is blue, but the other three can't be identified.

B Yes, ferric chloride is yellow, ferric chloride can identify sodium hydroxide, produce iron hydroxide precipitation, iron hydroxide can be added to the other two solutions, and one solution can be identified to dissolve iron hydroxide, that solution is hydrochloric acid, and the other is sodium chloride.

c No, you can only know which one is hydrochloric acid and calcium chloride, and you can't tell which is potassium carbonate and which is ammonia carbonate.

d does not react with each other at all, there is no phenomenon after mixing, and the observation is a colorless liquid, so it cannot be distinguished.

Therefore, the answer is B.

B Yes. Observe the color first, the yellow one is FeCl3, then pour the other three FeCl3, there is a reddish-brown precipitate is Naoh, and then pour the remaining two into the reddish-brown precipitate, the precipitate disappears is HCl, and the one that does not disappear is NaCl.

Pick D. The yellow one is FeCl3, and FeCl3 is added to the other three solutions, and the reddish-brown precipitate is NaOH, and then the other two solutions are added to the precipitate respectively, and the precipitate dissolves HCl, and the other is NaCl.

FeCl3+3NaOH=Fe(OH)3 +3NaClFe(OH)3+3HCl=FeCl3+3H2OABC could not be identified.

A, HCl, CuCl2, Nano3, Na2SO4 can only identify CuCl2B, BaCl2, Na2CO3, HCl, (NH4)2CO3 BaCl2 and carbonate all produce precipitation, and can be soluble in dilute hydrochloric acid.

C, FeCl3, HCL, NaCl, NaOH The yellow is FeCl3, and the addition produces a reddish-brown precipitate is NaOH, and the precipitate dissolves HCl, leaving NaCl

D, Na2CO3, Na2SO4, HCl, H2SO4 are indistinguishable between two acids.

Identification questions without other reagents, first look at the color, then consider mixing two by two, and then the identification test.

can be used as a known reagent. a.

CuCl2 solution is blue, but.

cucl2 with.

hcl、nano3、

na2so4

are not responsive, so they cannot be identified; c.

FeCl3 solution is yellow in color and is identified with it.

FeCl3 can be identified as a known reagent.

NaOH drops the remaining two bottles of solution into it.

FeCl3 and.

After the NAOH reaction, the tubes can be made to be generated.

fe(oh)

3 The precipitate dissolves is.

HCl, which does not dissolve. nacl

The answer is identified with NAOH.

Adding FeCl3 will cause colored precipitation (I forgot what color) and adding HCL will heat up, and you can feel it by touching the beaker.

There was no reaction to the addition of NaCl.

If the hydrochloric acid is added to the barium chloride, there will be a white precipitate, and there will be bubbles when added to the sodium carbonate, so as to identify the barium chloride, sodium carbonate and hydrochloric acid, and the ammonium carbonate has no obvious phenomenon.

C1 look at the color, FeCl32, add dropwise to the ferric chloride to identify and precipitate as sodium hydroxide 3 add the other two to the reflection reagent, the dissolved is hydrochloric acid 4, and the rest is the remainder.

Select C color yellow for ferric chloride, take three test tubes, add ferric chloride, and then add three other substances, the reddish-brown precipitate is sodium hydroxide.

Take two more test tubes, add iron hydroxide precipitate, and then add two other substances, so that the precipitate disappears is dilute hydrochloric acid, and the non-reaction is sodium chloride.

1 Answer choice c First of all, only the ferric chloride solution shows yellow, if it produces a reddish-brown precipitate with ferric chloride, it is a sodium hydroxide solution, and then add the remaining two solutions to the precipitate, if the precipitate dissolves hydrochloric acid, the other is sodium chloride.