How to compare the size of the ion concentration, the method and law of the comparison of the size o

Divide the strength and weakness, and look at **!

Ammonium chloride: chlorine corresponds to strong acid, ammonium corresponds to weak alkali (ammonium ion hydrolysis), so the chloride ion concentration is greater than the ammonium ion concentration; However, the hydrolysis process is also a relatively weak process, so the concentration of ammonium ions is greater than that of the particles produced by hydrolysis. But the hydrolysis of ammonium is greater than the ionization of water, so NH3H2O is greater than OH-, as for H+, NH3H2O, OH-, combined with the ionization of water and the hydrolysis of ammonium ions, H+** is more, so the concentration of H+ is greater than , OH-

In the case of ammonium sulfate, the ammonium ion concentration is greater than the sulfate ion concentration (compare from ** first).

The comparison of ion concentrations is a comparison of the size of various ions in a solution.

1. To analyze the solutes in the solution, there are acid solutions, alkali solutions, and salt solutions.

2. According to the nature of the solute, the strength, the degree of ionization, the degree of hydrolysis, the acidity and alkalinity of the solution, the ionization of water, etc.

3. Pay attention to the law of conservation of charge.

The methods and rules for comparing the magnitude of ion concentrations are as follows:

1) Conservation of electric charge.

In any electrolyte solution, the total number of negative charges carried by the anions is always equal to the total number of positive charges carried by the cations, i.e., the solution is electrically neutral. For example, in Na2CO3 solution, there is the following conservation relation:

c（na+）+c（h+）=c（oh-）+c（hco-3）+2c（co2-3）。

2) Conservation of materials.

In the electrolyte solution, because some ions can be ionized or hydrolyzed, the ions will change into other ions or molecules, etc., but the total number of atoms of a certain special element contained in these ions or molecules is always unchanged and is in line with the conservation of atoms. For example, there is the following conservation relationship in K2S solution:

c（k+）=2c（h2s）+2c（hs-）+2c（s2-）。

3) Conservation of protons.

The c(h+) and c(oh-) ionized by water are always equal, and the total amount of h+ and oh- ionized by water in the solution is still equal although they are combined with other ions.

For example, there is the following conservation relationship in K2S solution: C(OH-)=C(H+)+C(Hs-)+2C(H2S). (Actually, the conservation of protons can be introduced by the combination of "conservation of charge" and "conservation of materials").

Logarithmic determination of free Cu and PB measurements:

From the comparison of the results of the logarithmic measurement of the measured values of free Cu and Pb with the estimated results of WinHumicV, it can be seen that the free state concentrations of CD2+ and Zn2+ measured by the Taonan membrane technology are in good agreement with the results calculated by the WinHumicv model, while the free state concentrations of Pb2+ and Cu2+ are slightly higher than those calculated by the model.

For example, Pb2+ and Cu2+ in the free state are more affected by the organic matter or soluble organic carbon in the soil than the CD2+ and Zn2+ in the free state, which may lead to the difference.

The comparison of the ion concentration magnitude in the solution is as follows:

First, the key points of thinking.

The key points of thinking for solving the problem of the comparison of ion concentration in solution can be summarized as follows: closely following a relationship (the inequality or equality relationship of ion concentration and magnitude comparison), grasping two key points (ionization, hydrolysis), and paying attention to three conservation formulas (conservation of charge, conservation of materials, conservation of protons).

Second, the specific idea of solving the problem.

1. Look at whether there is a reaction in the electrolyte solution and determine the type of solute; Second, look at the ionization and hydrolysis of solutes to determine the relationship between ion concentration and size; Third, look at what kind of conservation relationship it belongs to, and determine the concentration equation relationship.

2. Single solution: if it is an acid or alkali solution, consider ionization (note that the weak electrolyte is weakly ionized); If it is a salt solution, ionization should be considered first, and then hydrolysis should be considered (note that the hydrolysis of salt is weak); In the case of weakly acidic acid salts, both ionization and hydrolysis are considered.

3. Non-reactive mixed solution: consider ionization and hydrolysis at the same time.

4. Mixed solution with reaction: if it happens to be completely reacted and the acid or base is generated, ionization is considered; If salt is generated, hydrolysis is considered. If there is an excess of reactants, ionization or hydrolysis is considered according to the degree of excess.

Third, there are problems.

1. It is difficult to distinguish between strong and weak electrolytes.

Strong acids, strong bases, and most salts (whether they are strong acids and weak alkali salts or weak acids and strong alkali salts, etc.) are strong electrolytes, completely ionized, and the ion concentration is analyzed according to the composition of the electrolyte; Weak acid, weak alkali and water are weak electrolytes, weak ionization, and the ionization equation should be written with a reversible number, and the ion concentration should be analyzed according to the ionization equilibrium.

2. It is not clear whether the electrolyte is ionized or hydrolyzed.

Both strong and weak electrolytes can be ionized, and salts containing anions with weak acids or cations with weak bases are hydrolyzed. Anions of weak acids or cations of weak bases are present in weak acid or weak base solutions, but hydrolysis does not occur. The multi-weak acid is ionized step by step, and the first step ionization is the main one.

The multiple weak acid ions are hydrolyzed step by step, and the first step hydrolysis is the main one.

To judge the concentration of ions in the same solution, the following aspects should be considered.

1.Determine the acidity and alkalinity of the solution.

As. Concentrations of 4 ions in NAF solution.

First of all, it is judged that NAF is a weak acid.

Strong alkaline salt, hydrolysis is alkaline, C(OH-)>C(H+)Na+ is not hydrolyzed while F- will be hydrolyzed, therefore.

c(na+)>c(f-)

Na+ and F- are the main ions, therefore.

c(na+)>c(f-)>

c(oh-)>c(h+)

2.Utilize the conservation of charge.

NH4Cl solution is electrically neutral because.

c（nh4+）+c(h

c(cl-)+c(oh-)

And because the solution is acidic, c(oh-).

c(h+), then.

c（nh4+）c(nh4+)>c(h+)>c(oh-)3.Grasp the main factors, use the conservation of charge and the conservation of materials.

Such as the amount of concentration of other substances.

Mixed solution of NAF and HF.

Acidic, judging c(f

and c(hf).

It can be judged from the second article above.

c(f-)>c(na+)

c(h)>c(oh-)

Conservation of materials is then used2

c(na+)=c(f-)+c(hf)

Comprehensive, got. c(hf)

c(hf)。

Or to understand it directly, because the solution shows acidity, indicating that the ionization of HF is dominant.

hf《==h+

f- and the hydrolysis of f- is secondary, f-+

h2o《==

hf+oh-

So. c(f

c(hf)

1.Salt is a substance that is completely ionized when put into water.

Whether it is a strong acid and a weak alkali salt or a strong alkali and a weak salt.

Let's say ammonium bicarbonate.

Put it in water to ionize the ionized ions and bicarbonate ions.

It should be noted that:

Both carbonic acid and acidic salts of carbonic acid are mainly hydrolyzed.

But. Both sulfuric acid and acid salts of sulfuric acid are dominated by electricity.

Because it is a strong acid.

Ammonium bicarbonate is ionized in water after pressing the ion and bicarbonate ion.

Bicarbonate ions are hydrolyzed.

Bicarbonate ions are hydrolyzed to produce carbonic acid.

However, the degree of hydrolysis is small.

So all exist in the form of carbonic acid molecules.

2.You look at what the hydrolysis of carbonate ions produces.

Bicarbonate ions, which are then rehydrolyzed by bicarbonate ions.

Carbonic acid is generated. Hydrolysis is mainly based on the first step, so the degree of hydrolysis in the first step is much greater than that in the second step, so the degree of hydrolysis of bicarbonate ions is not as large as that of carbonate ions.

There is also double hydrolysis, for example, ammonium bicarbonate, bicarbonate ion hydrolysis, the generation of hydroxide ions, ammonium ions are also hydrolyzed, to generate hydrogen ions, but the bicarbonate ions are combined with the hydrogen ions in the water, and the ammonium ions are combined with the hydroxide ions in the water, if they react like this, promote the ionization of water, so that the concentration of hydroxide ions and hydrogen ions in the water increases, according to the principle of Le Chartrete, the degree of hydrolysis of bicarbonate ions and ammonium ions increases.

And there's more. To deal with this kind of problem, you also need to look at the amount of weak electrolyte in the solution.

There are 2mol ammonium ions in the ammonium sulfate solution and 1moi ammonium ions in the ammonium chloride solution, and the ion concentrations of their hydrolysis are different.

For example, Na2CO3 solution.

Na+ and carbonate ions are dominant ions, H+ and OH- are recessive ions, and the former number is the latter.

Number of dominant ions, recessive ions).

Sodium ion carbonate.

Here it is clear that there are 2 NAs and 1 carbonate.

Note: Sometimes it is judged by hydrolysis (NaHCO3, Na+HCO3-, this is because HCO3- to be hydrolyzed).

Carbonate HCO3-

One-step hydrolysis Two-step hydrolysis.

oh-＞h+

According to the acidity and alkalinity of the solution.

So [na+] CO3

＞hco3-]＞oh-]＞h+]

Acetic acid with 100 ml

Hydrogen hand clear sodium oxide.

The solution is mixed with the amount of acetic acid of the substance.

The amount is equal to the amount of NaOH substance, so it is equivalent to sodium acetate solution when mixed. The ions in sodium acetate solution are Na+, acetate ion, H+, and Oh-. Obviously, Na+ is the most, and the acetate is less than Na+ due to partial hydrolysis, and the hydrolysis is very little, so oh- is less than acetate, and the solution is alkaline, so oh- is greater than H+.

Ion concentration order is NA+>CH3COO->OH->H+

2. It is best to add an equal volume to mix this question. Mix the solution.

The ions present in are also Na+, acetate ions, H+, and Oh-. If acetic acid is not ionized and acetate is not hydrolyzed, Na+ and acetate concentrations are the same. Since the ionization of acetic acid is stronger than the hydrolysis of acetate, the ionized acetate is more than the hydrolyzed, so the total acetate increases, resulting in acetate greater than Na+.

Since acetic acid ionization is stronger than acetate hydrolysis, the ionized H+ is more than the OH- produced by hydrolysis, so H+ is greater than OH. Ion concentration magnitude order: CH3CoO->Na+>H+>OH-

3. Take NaHCO3 as an example. HCO3- is ionized (producing CO32-) and hydrolyzed (producing H2CO3) but is rarely present and is basically present as HCO3-. Mass balance: [HCO3-]+CO32-]+H2CO3]=

Charge balance: [Na+]+H+]=HCO3-]+OH-]+2[CO32-].

4. Take MGO as an example:

fe3+3h2o

3h+fe(oh)3↓

It can be seen that if Fe3+ is removed, only the H+ concentration needs to be reduced, and the reaction can be carried out to the right.

The following reaction occurs when the MGO is added:

mgo2h+

Mg2+H2O, just enough to consume H+ and promote the hydrolysis of Fe3+. Similar to MGCo3, of course MG(OH)2Y is also possible.

The latter one is similar to the front.