Is there an easy way to tell if ions or substances can coexist in large quantities in water?

Ion Coexistence To determine the problem of ion coexistence, you should first look at the prerequisites of the test questions, such as "in a strong acidic solution......"...... in a colorless transparent solution"...... in a solution of C(H+):1 10-13Mo1 L-1 ionized by water"...... due to redox reactionsAnd so on, and then analyze the interaction between the ions.

Whether a variety of ions can coexist in the same solution in large quantities can be summed up in one sentence: one color, two sexes, three specials, and four reactions. 1 One color.

i.e. the color of the solution. If the colorless solution is confined, non-ferrous ions such as Cu2+, Fe3+, Fe2+, and Mno4 cannot exist. 2 Two sexes.

That is, the acidity and alkalinity of the solution.

In strong acidic solutions, OH- and weak acid anions (such as CO32—, SO32—, S2, CH3COO, etc.) cannot exist in large quantities;

In strong alkaline solution, H+ and weak alkaline cations (such as NH4+, Al3+, Mg2+, Fe3+, etc.) cannot exist in large quantities;

Acidic weak acid ions (such as HCO3—, HSO3—, HS, H2PO4, etc.) cannot exist in large quantities in strongly acidic or alkaline solutions.

3 Sante. Refers to three special cases.

A1O2 – and HCO3 – cannot coexist in large quantities: A1O2—+HCO3—+H2O=A1(OH)3 +CO2

The "NO3—+H+" combination has strong oxidizing property and can react with S2-, Fe2+, I—, etc., while this combination is often hidden and not easy to be detected.

In the combination of NH4+ and CH3COO, CO32—, Mg2+ and HCO3—etc., although both ions can be hydrolyzed and the hydrolysis promotes each other, the total degree of hydrolysis is still very small, and they can coexist in large quantities in solution (heating is different).

4 Four reactions. Refers to the four types of reactions that can usually occur between ions, and ions that can react with each other obviously cannot coexist in large quantities.

Metathesis reactions, such as Ba2+ and SO42—, NH4+ and OH, H+ and CH3COO, etc.;

Redox reactions, such as Fe3+ and I—, No3—(H+) and Fe2+, Mno4, (H+) and Br, H10 and S2O32—etc.;

Double hydrolysis reactions, such as A13+ and CO32, Al3+ and AlO2, etc.;

Complexation reactions, such as Fe3+ and SCN—etc.

The main basis is whether there will be a chemical reaction to produce precipitation, water, gas or redox reactions.

1. In a strong acidic solution, there can be a large number of weak acid ions: such as carbonate (CO32), bicarbonate (HCO3), sulfide ion (S2), hydride ion (HS), sulfite ion (SO32), silicate ion (SiO32), metaaluminate ion (ALO2), fluoride ion (F), etc., nor can there be a large number of hydroxide (OH).

2. In a strong alkaline solution, there can be no weak alkali metal ions in large quantities. For example, magnesium ions (Mg2+), ferrous ions (Fe2+), aluminum ions (Al3+), copper ions (Cu2+) and ammonium ions (NH4+), etc., can not exist in large quantities of hydrogen ions (H+) and acid root ions

HCO3, HSO3, HS, H2PO4, etc.

Substances that are difficult to ionize are generated

If some ions in the solution are bound to substances that are difficult to ionize, then these ions in the solution cannot coexist in large quantities.

Common ions that are prone to ionization are as follows:

1) H+ cannot coexist with OH-, Clo-, CH3CoO-, F-, S2-, HCO3-, CO32-, HSO3-, HS-, S2-, H2PO4-, HPO42-, PO43-, F-, HSIO3-, SiO32-.

2) OH- cannot coexist in large quantities with H+, Cu2+, Fe2+, Fe3+, Mg2+, Al3+, HCO3-, HS-, H2PO4-, HPO42-, and HSIO3- due to the formation of weak alkali and water.

Ions in solution cannot react to form water, gas, precipitate.

1.In a strongly acidic solution, weak acid ions cannot be present in large quantities.

2.In a strong alkaline solution, there should be no weak alkali metal ions in large quantities.

3.Ions that can undergo redox reactions cannot coexist.

First of all, you should remember that all the precipitates, weak ionizers and gas-producing substances cannot coexist in aqueous solution, and strong oxidizing substances and reducing substances cannot coexist, once nitrate ions and H ions meet in aqueous solution, just like when there is strong oxidizing nitric acid, it cannot coexist with reducing ions, such as ferrous ions and sulfur ions. If you can't see the lack of accumulation, just ask the teacher more questions.

First of all, it is necessary to see what the solution shows, and then judge according to the ionic properties.

The method of judging a large number of coexisting ions is as follows:1. Look at the additional conditions, such as the color of the solution, if it is a colorless solution, then the colored ions such as Mno4, Fe3, Cu2, Fe2 and so on cannot exist in large quantities; acidity and alkalinity of the solution; the presence of specific ions or molecules, etc.

Second, look at the reaction - whether the given ions can react with each other. Memorize several situations in which ionic reactions cannot coexist in large quantities.

Redox reaction: Fe3 can oxidize S2-, I, etc.; Mno4 and CLO have strong oxidation under acidic, alkaline and neutral conditions, and can oxidize I, Fe2, SO32, etc. Double hydrolysis of salts:

Al3 is completely hydrolyzed with AlO2, HCO3, CO32, S2-, HS, etc.; Fe3 is hydrolyzed with ALO2, HCO3, CO32, etc., and cannot coexist in large quantities.

3. "5 points" special reminder.

1. Clear solution does not mean colorless.

2. The solution containing a large amount of Fe3 is implicitly an acidic solution and has strong oxidation.

3. The solution containing a large amount of NO3 has strong oxidation under implicit acidic conditions.

4. A solution containing a large amount of ALO2 is implicitly an alkaline solution.

5. Ions that can undergo double hydrolysis reaction may also coexist in large quantities.

Methods for judging ion coexistence:

The so-called whether several ions can coexist in the same solution means that there is no reaction between the ions, and to solve this kind of problem, we must pay attention to the prerequisites in the title, which are summarized as follows:

1) Look at the question of the question, such as "can coexist in large quantities", "cannot coexist in large quantities", or "may coexist in large quantities", etc.

2) Clarify the qualifications of the question, such as:

If the color of the solution is limited, if the problem is colorless and transparent, there must be no Fe2+ (light green), Fe3+ (brownish-yellow), Cu2+ (blue), Mno4 (purple) and other ions; Also note that "transparent" is not "colorless".

Limit the acidity and alkalinity of the solution, a"In a strongly acidic (or pH 1) solution", that is, it contains a large amount of H+, H+ should be taken into account, and neither OH nor weak acid ions can coexist in large quantities.

b."In a strong alkaline (or pH 14) solution", that is, it contains a large amount of OH, OH should be taken into account, and H+ and weak alkali cations cannot coexist in large quantities.

c."In a solution ionized from water to C(H+) 1 10 10 mol l, or in a solution ionized from water to C(OH) 1 10 10 mol l", that is, a group of ions that can coexist in large quantities under acidic or alkaline conditions;

d."In a solution that reacts with Al to produce H2", in fact, in a solution under acidic or alkaline conditions (except nitric acid);

e."Solutions that can dissolve Al2O3 or Al(OH)3" are solutions that contain a large amount of H+ or Oh, in fact, in solutions under strong acid or alkaline conditions;

f."In neutral solution", ions that cannot exist in large quantities in neutral solutions, such as weak basic cations such as Al3+, Fe3+, Cu2+, etc., are essentially acidic, and they cannot exist in large quantities in neutral solutions; Weak acid anions such as clo, CO32, and PO43 are essentially to make the solution alkaline, and they cannot exist in large quantities in neutral solutions.

Define the type of reaction.

...... due to redox reactionsThat is, only the redox reactions between ions are considered;

Limit the ions already present in the solution.

If "Fe3+ and Cl are already present in the solution", then OH, SCN, and Ag+ ions cannot coexist in large quantities.

1) Cannot coexist in large quantities due to the formation of gases, such as H+ and <>

s 2－ 、hco<>

hso<>

HS and so on cannot coexist in large quantities

2) Cannot coexist in large quantities due to the formation of precipitates, such as AG+ with Cl Bri I BA2 with <>

<>Cu2+ with S2, OH, etc

3) It cannot coexist in large quantities due to the formation of refractory ionization substances, such as H+ and Clo Fs2, HCO<>

co<>

and so on to generate weak acids; OH is <> with NH

Cu 2+, Fe 3+, etc. form weak bases; H+ with OH to produce water

4) It cannot coexist in large quantities due to redox reactions, such as Fe3+ and S2, IfE2+ and H+ No<>

5) Unable to coexist in large quantities due to the influence of acidic and alkaline environment, such as weak acid ions cannot exist in acidic solution; Acid root ions of weak acids cannot exist in acidic and alkaline solutions

6) If it is a colorless solution, it is necessary to exclude colored ions such as Cu2+, Fe3+, Fe2+, MNO<>

1. First of all, see if there is a precipitation, if there is a precipitation, it is generally a dissolvable precipitation or an insoluble precipitation, including silver chloride, barium sulfate and so on. The dissolvable precipitate will quickly disappear when acid, alkali or salt is released.

2. Then it depends on the color of the solution, first of all, if the color of the solution is yellow, it may be iron ions, copper cavity ions. If the solution is colorless and transparent, there may be no iron or copper ions.

3 The next thing to look at is whether it generates gas, and if so, it may be the action of hydrogen ions and carbonate ions.

4 The next step is to measure with a laboratory instrument, does it produce water? If the raw reed is turned into water, it means that there are hydrogen ions and hydroxide ions in it.