A few questions about ion coexistence, how to do this kind of problem?

1. The following groups of ions can coexist in large quantities in aqueous solution (a).

a）na+、ba2+、oh-、alo2- （b）h+、na+、cl-、so32-

c）h+、na+、hpo42-、no3- （d）k+、ca2+、clo-、

Solution: +SO32- = H2O + SO2

NO3- = HNO3, oxidizing + strongly acidic, HPO42- is oxidized.

SO42- =CaSO4 microlytic precipitate.

2..The following groups of ions can coexist in large quantities in aqueous solution (c).

a）al3+、so42-、hco3-、no3- （b）nh4+、cl-、sio32-、so42-

c）nh4+、no3-、ch3coo-、hco3- （d）fe3+、cl-、hco3-、no3-

Solution and HCO3- cannot coexist, and mutual hydrolysis will occur. Al(OH)3 precipitate + CO2 gas is then generated.

and SiO32- cannot coexist, and mutual hydrolysis will also occur. Then NH3 gas + H2SiO3 precipitate.

and HCO3- cannot coexist, and again there is a mutual promotion of hydrolysis. Fe(OH)3 precipitate + CO2 gas is then generated.

This question is obviously a ...... of double hydrolysis

3. The following groups of ions cannot coexist in large quantities in aqueous solution (BC).

a）na+、mg2+、no3-、i- （b）h+、fe2+、no3-、cl-

c）na+、k+、clo-、s2- （d）h+、fe2+、so42-、i-

Solution: +NO3- = HNO3 has strong oxidizing properties and can oxidize Fe2+ to Fe3+

It is oxidizing, and S2- oxidizes to S.

4. Among the following groups of ions, a large number of ions can coexist in the solution of [H+]=10-13mol L-1, and the gas and precipitation will be produced during the addition of NaHSO4 solution (C).

a）na+、no3-、alo2-、cl- （b）na+、k+、no3-、sio32-

c）k+、cl-、alo2-、co32- （d）na+、mg2+、hco3-、cl-

Solution: H+]=1 10-13mol L-1, that is, pH=13, obviously alkaline.

OH-=mg(OH)2 precipitate, exclude.

When the amount of NaHSO4 added is sufficient, the solution becomes acidic.

Outcome. Precipitation in acidic environments.

2- Acidic environment generates silicic acid precipitate.

c.Acidic environment CO3 2- becomes CO2 gas, and ALO2- such as a precipitate. In this way, it fits the topic. Above.

Sulfurous acid weak.

c Phosphite weak acid.

d Calcium sulfate precipitation.

Medium ALO2- and HCO3- cannot coexist.

Fe2+, NO3- and HSO3- in B and C cannot coexist.

Fe3+ and SCN- in C

Can't coexist. Pick D

The redox reaction of S2O32- occurs under acidic conditions.

In B, Al3+ and HCO3- are bihydrolyzed Al3+H2OAL(OH)3

h+hco3-

h2oh2co3

HSO3- in OH-C

Does not coexist with H+.

Therefore, magnesium ions are selected not to coexist with hydroxide ions.

Bicarbonate does not coexist with hydrogen ions in c.

d nitric acid oxidizes ferrous ions. Pick B

1b hydrogen ions and sulfite ions can react to form water and sulfur dioxide.

1c hydrogen ions and hydrogen phosphate ions can react to form dihydrogen phosphate ions or phosphoric acid.

1d calcium ions and sulfate ions can react to form calcium sulfate, which is slightly soluble.

2A aluminum ions and bicarbonate ions can be double hydrolyzed to form aluminum hydroxide and carbon dioxide.

2b ammonium ions and silicate ions can be double hydrolyzed to generate ammonia and silicic acid (precipitation) 2d iron ions and bicarbonate ions can be double hydrolyzed to generate iron hydroxide and carbon dioxide.

3b hydrogen ions and nitrate together are oxidizing, ferrous ions are reducing, and the reaction produces ferric ions, nitric oxide and water.

3C hypochlorite ions are oxidizing and sulfur ions are reducing, and the reaction produces chloride ions and sulfur.

4. After adding sodium bisulfate (acidic), A and B have precipitation, which are aluminum hydroxide and aluminic acid, respectively, D has gas, which is carbon dioxide, and C has both precipitation and gas, which is aluminum hydroxide and carbon dioxide.

Whether ions can coexist in large quantities in solution involves comprehensive knowledge of the properties of ions and the acidity and alkalinity of the solution. Anything that can cause a significant change in the concentration of relevant ions in the solution due to the reaction cannot coexist in large quantities. For example, insoluble, difficult-to-ionize, gaseous substances may be converted into other kinds of ions (including oxidation-reduction reactions).

Generally, the following aspects can be considered.

1 Weak base cations are only found in more acidic solutions. For example, Fe3+, Al3+, ZN2+, Cu2+, NH4+, Ag+, etc. are not compatible with OH-.

Massive coexistence. 2 Weak acid anions are only found in alkaline solutions. For example, CH3COO-, F-, CO32-, SO32-, S2-, PO43-, and AlO2- are all associated with H+

It is not possible to coexist in large quantities.

3. The acid anion of weak acid cannot coexist in large quantities in a solution with strong acidity or alkaline. They are weak when exposed to strong acids (H+).

acid molecules; When encountering a strong alkali (oh-), positive salt and water are generated. Such as: HSO3-, HCO3-, HS-, H2PO4-, HPO42-, etc.

4 If anions and cations can combine with each other to form insoluble or slightly soluble salts, they cannot coexist in large quantities. Such as: Ba2+, Ca2+ and CO32-,

SO32-, PO43-, SO42-, etc.; ag+ and cl-, br-, i-, etc.; Ca2+ with F-, C2O42-, etc.

5 If the anion and cation undergo double hydrolysis reaction, they cannot coexist in large quantities.

Weak electrolytes can be generated.

Precipitated gases cannot coexist.

No reactions: metathesis reaction, redox reaction, complexation reaction, double hydrolysis reaction;

In fact, this kind of question is to consider whether the ions in the stem or option will react with each other.

Sometimes the stem will remind you of the acidity and alkalinity of the solution, but it's still the same, so you add hydrogen ions or hydroxide ions to each option.

As for the reactions to the regular test, those are still the types. Some are redox reactions, as for whether the redox reaction occurs, you can refer to the redox properties of each ion in an acidic environment or alkaline environment, and you can refer to the element activity order table. In addition, the reaction that often occurs in solution is the metathesis reaction.

Ions cannot coexist in large quantities, nothing more than the formation of weak electrolytes, gases, insoluble substances, etc. This is where you need to react with each other.

Judging the activity of the elements according to the periodic table, plus the stability of the products of anion and ionic bonding, and paying attention to the conditions for the presence of ions (such as whether there is water·· ）

Option A analysis: It can react with NaOH to produce a gas that can make the wet red litmus test paper turn blue, indicating that there is NH4+ in the original solution, and the reaction with FeCl3 solution to form egg yolk precipitate means that there is S2-(2Fe3+ +S2-====2Fe2+ +S in the original solution), so B is incorrect, because hypochlorite has strong oxidizing property and will oxidize sulfur ions. C error, 2H+ +S2-===H2S, D error, 2AG+ +S2-===AG2S

The acid ions, which can produce acid gases, only have CO3 in the above answer, so choose A

A solution reacts with NaOH to form a gas that turns wet red litmus paper blue, which contains NH4+

It can also react with FeCl3 solution to form egg yolk precipitate, which has S2-S2- reducibility, does not coexist with Clo-, H+ +NO3-, NH4+AG++OH- will produce silver ammonium, and will not produce NH3

To choose D, we must first clarify a point of view: those that will react with each other cannot be in the same factory, and the reasoning can be obtained:

It does not coexist with OH-, so it cannot be in the same factory.

It does not coexist with CU2+, so it cannot be in the same plant.

So if a factory has it.

H+, so there is factory B.

OH- due to the fact that OH- and Cu2+ do not coexist.

So Cu2+ is in plant A together with H+, so H+ and Cu2+ are added from the same plant: it's nitric acid, but nitric acid is a solution, no water, precipitation, gas survives! I can coexist 2The conditions for coexistence are the absence of water, gas, and precipitation.

3.Because only anions and cations have a solution will be stable and electrically neutral! If there is charge, agglomeration will occur (I don't seem to talk about it in junior high school), just remember that electricity is neutral!

If it is from the same factory, it is inevitably impossible to react, so the two options of AB are excluded.

If it's c, then there must be hydrogen ions in the other plant, so the hydroxide reacts regardless of where it is generated, so c is excluded, and the answer is d

Analysis: If factory A has H, then there is no OH, that is, factory B has OH. Cu2+ cannot be in factory B, so it is in factory A.

Factory A now has H, Cu2+, and lacks anions, so there is NO3. Plant B must also have cations, so there must be K, a total of three ions, so there is NO3.

That is, factory A: H, Cu2+, NO3

Factory B: OH, NO3, K

For this question, D should be selected.

The solution is not charged, so there must be both anions and cations, and hydrogen ions cannot be together with hydroxides.

Hydroxide cannot be combined with hydrogen ions.

So choose D

Nitrate ions are combined with H+ in a solution of pH=1 to form nitric acid, which has strong oxidizing properties and can oxidize 2-valent iron to 3-valent iron.

Nima, too much in a typical. Can the solution that dissolves the aluminum sheet and produces hydrogen gas coexist: NO3+, Na+, Mg+ Would you do it?

You can use the review materials of this year's senior year to conduct thematic review, consolidate knowledge points, and carefully look at example questions and do typical questions. Hopefully, my advice will be helpful to you in your studies.

The premise that ions can coexist is that no chemical reaction occurs.

The question of ion coexistence, basically the question will be given:

1) What can not (can) coexist in large quantities under acidic conditions? (Whichever option is added, plus h+).

2) What is the one that cannot (can) coexist in large quantities under alkaline conditions? (Either option, plus oh-).

3) Which of the following ions cannot (can) coexist in large quantities?

To do this type of question, first look at what kind of question it is, and then look at whether each set of options can produce gases, precipitates and weak electrolytes (water) and whether redox reactions can occur.

One by one, see if there are any that do not coexist, and mark them to prevent confusion

Common test: ammonium-hydroxide, barium ion-sulfate, hydrogen ion-hydroxide, silver ion-chloride ion, carbonate-hydrogen ion, bicarbonate-hydrogen ion, iron ion-hydroxide, magnesium ion-hydroxide, aluminum ion-hydroxide (not excessive), copper ion-hydroxide, metal ions other than sodium ions, ammonium potassium ions, carbonate strongly oxidizing ions, strongly reducing ions.

Incomplete words remind me 、、、

These are the ones that cannot coexist.