Chemistry problems in junior high school. About the test ions.

First of all, you need to figure out what ions and what ions you want to test. Then the factors that have an influence on each other should be eliminated first.

For example, to test cl-. The first thing to do is to rule out the influence of other ions. To add dilute nitric acidification first, then add silver nitrate.

To test Ba2+, dilute hydrochloric acid should be added to exclude the influence of other ions, and then dilute sulfuric acid or soluble sulfate should be added.

No matter what ions are tested, they must be. First of all, we must rule out other influencing factors before testing.

It must be noted that: To form those precipitations that are more common to everyone. For example, barium carbonate is also a precipitate.

However, the general way to test carbonate is not to add Ba2+ to test. Instead, dilute hydrochloric acid is added. It produces colorless and odorless gas that can make clarified lime water turbid.

Method 1: Take two solutions with two test tubes, and then add dilute hydrochloric acid, the sodium carbonate solution produced by gas is the sodium chloride solution, and the sodium chloride solution is not the phenomenon.

Method 2: Take two solutions with two test tubes, and then add silver nitrate solution and dilute nitric acid, there is a white precipitate to produce sodium chloride solution, and no precipitate to produce sodium carbonate solution.

Or barium is an example, it can precipitate with carbonate and sulfate, but barium carbonate is insoluble in water but soluble in acid, so it should be tested with dilute nitric acid. Similarly, silver and chlorate and carbonic acid are precipitated, so dilute hydrochloric acid should be used to test whether it is silver chloride.

You can't use silver nitrate as you say, both bottles have precipitation.

Hydrochloric acid is OK, and reacts with sodium carbonate, but not with salt water.

If silver chloride is generated, it is insoluble in dilute nitric acid.

I didn't understand your last question, sorry.

You just remember it directly: just test the silver nitrate acidified with nitric acid to test the CL ions, and if there is a white precipitate, it must be the CL ions.

1. Hydrogen ion (acid): add purple litmus test solution dropwise and add zinc grains.

2. Hydroxide ion (alkali): phenolphthalein test solution copper sulfate solution.

3. Carbonate ions: dilute hydrochloric acid is added, and the gas produced passes through the clarified lime water, and the clarified lime water becomes turbid, which is carbonate ions.

4. Chloride ions: add silver nitrate solution to produce white precipitate, and then add dilute nitric acid, if the precipitate is insoluble, it is chloride ions.

5. Sulfate ions: barium nitrate (or barium chloride) solution, producing white precipitate, and then adding dilute nitric acid, if the precipitate is insoluble, it is sulfate ion.

6. Ammonium ions: sodium hydroxide solution and heating, put the moistened red litmus test paper at the mouth of the test tube, the red litmus test paper turns blue, which is ammonium ion.

In general, the detection of ions can be divided into several categories of methods:

1. Indicator (used to judge acid, alkali).

2. Gas method (e.g. carbonate, etc.).

3. Precipitation method (such as chloride ions, sulfate ions, etc.).

Eh, the distinction between acid-base ions that you are learning in the third year of junior high school is whether they are acidic, alkaline or neutral, and we can use the corresponding indicators to distinguish them, such as phenolphthalein indicators, methyl orange indicators, or litmus indicators.

When it is an acidic ion: adding phenolphthalein is colorless, you can add methyl orange, and red means that it is an acidic salt. Add litmus indicator.

The color changes to red.

When it is an alkaline ion: adding phenolphthalein is red, and adding litmus is also blue.

Just add the indicator. Litmus is "acid red alkali blue".

Phenolphthalein is "acidic colorless alkali red".

Ion testing.

1. Hydrogen ions: add purple litmus test solution dropwise and add zinc grains.

2. Hydroxide ion: phenolphthalein test solution, copper sulfate solution.

3. Carbonate ions: dilute hydrochloric acid and clarified lime water.

4. Chloride ions: silver nitrate solution and dilute nitric acid, if white precipitate is produced, it is chloride ions 5. Sulfate ions: barium nitrate solution and dilute nitric acid First add dilute hydrochloric acid dropwise and then drop into barium chloride 6, ammonium ions:

Sodium hydroxide solution and heat, put the moist red litmus test paper on the mouth of the test tube 7, copper ions: add sodium hydroxide solution dropwise, if it produces blue precipitate, it is copper ion 8, iron ions: add sodium hydroxide solution dropwise, if it produces reddish-brown precipitate, it is iron ions, then you look at this.

A silver ion touching the carbonate should also be precipitated.

b barium meets carbonate is also a precipitate.

The generation of copper sulfate by CCU ions and hydroxide ions is a blue precipitate d sodium sulfite and sulfuric acid reaction with SO2

It is also a colorless gas.

So C should be chosen

c1.False, it may be CO32-, and the dropwise addition of silver nitrate solution will also produce a white precipitate2False, it may be CO32- or SO32-, and the dropwise addition of barium chloride solution will also produce a white precipitate3Correct, the base is only copper hydroxide blue.

4.Error, probably so32-, so2 is also colorless.

The first question: hydrochloric acid can also be used, there is gas to produce sodium carbonate, and there is no phenomenon of sodium chloride. This is simpler, this is actually the test of carbonate ions and chloride ions, because cations are sodium ions, so by testing anions can distinguish substances.

However, if only silver nitrate is used, it cannot be identified, because sodium chloride and sodium carbonate can react with silver nitrate to form a white precipitate, so with silver nitrate, we also need to add acid to the precipitate to see if the precipitate capacity is dissolved, the insoluble is silver chloride, and the dissolved is silver carbonate.

The second question: the general test of chloride ions is silver nitrate and hydrochloric acid, in junior high school we have two insoluble salts in acid, silver chloride and barium sulfate, but can and silver ions, barium ions to produce precipitation and carbonate ions, that is, barium carbonate and silver carbonate, such as the identification of sodium carbonate and sodium sulfate, if we choose to use barium nitrate identification, then both solutions can produce white precipitate (barium carbonate and barium sulfate) with barium nitrate, so it can not be identified, at this time, we add nitric acid to the precipitation respectively, It is barium carbonate that produces gas (which can also be said to be precipitated and dissolved), that is, the original solution is sodium carbonate, and what is insoluble is barium sulfate, that is, the original solution is sodium sulfate.

I hope it can help you, so if you don't understand, you can continue to ask.

When Cl+ is present in this solution.

Hydroxide ion test, first of all, from the acidity and alkalinity consideration, a solution is alkaline must have hydroxide ions, then the test method is to add some phenolphthalein test solution, if it turns red, it is alkaline, then contains hydroxide ions.

Other ions are also solved in the same way from his characteristics, and then hydrogen ions, then you first have to consider what characteristics it has, remember, it is the characteristics, if you want hydrogen ions can be oxidized into hydrogen, then this is not its characteristics, there are too many gases, this does not explain the problem, and you also prove that this gas can ignite with oxygen, generate water and do not produce other substances, which is too troublesome. The characteristic of hydrogen ions is that they are acidic, that is, all acidic solutions must have hydrogen ions. Knowing this feature, then it can be solved.

Take an appropriate amount of solution and drop it into the purple litmus test solution, if it turns red, it contains hydrogen ions, if it does not change or turns blue, there are no hydrogen ions (there must be hydroxide ions when it turns blue).

You can also look at the color and other aspects, for example, if you are asking about junior high school, then if I remember correctly, junior high school has such a few specific colored solutions, that is, some ion characteristics, for example, the solution is pale yellow, then there are iron ions; The solution is pale green, so there are ferrous ions; The blue color has copper ions.

Methods such as precipitation are generally not used unless it is expressly stated that there is a certain range within which precipitation is a characteristic. Or this precipitate is different from other precipitates and has properties, such as anhydrous copper sulfate (white precipitate) turns blue when exposed to water.

Cl-AgNO3+Hno3SO42-BaCl2+HClCO32-HCl, the gas is generated through the clarified lime water Fe3+ Naoh to produce a reddish-brown precipitate Cu2+ NaOH to produce a blue precipitate.

In the absence of ambiguity, the test ions should ensure that the phenomenon is obvious after the reaction, that is, the formation of precipitates, gases or ions with unique colors, and can also be detected with test strips.

Reaction that uses chromogenic reaction or precipitation.

Developing, precipitating, and generating gases.