What is a double hydrolysis reaction? As the title suggests, thank you

The hydrolysis of weak acids and weak alkali salts is more complicated, and it is not introduced in middle school textbooks, but it may be tested in the college entrance examination. For example, comparing the concentration of ammonium ions in ammonium chloride and ammonium bicarbonate solutions of the same concentration, why aluminum ions and bicarbonate ions cannot coexist in the solution. Why is that?

Because this kind of question is prepared from the perspective of the influence of external conditions on hydrolytic equilibrium, it does not exceed the teaching requirements of secondary schools. This is the case with the double hydrolysis reaction. Most of the weak acids and weak alkali salts, although the hydrolysis of anions and cations promote each other, the degree of hydrolysis is still not large, such as ammonium bicarbonate, which can be prepared into a solution.

Some cations and some anions in the solution can make the hydrolysis reaction tend to be complete due to the mutual promotion of the hydrolysis reaction, and this kind of reaction is the double hydrolysis reaction. Which cations and which anions can be dihydrolyzed in solution? In the solubility table of some acids and alkalis in the textbook, there are aluminum ions, iron ions and carbonate ions marked with "-", which can undergo double hydrolysis reaction, and the reaction that occurs when foam fire extinguishers are used is also double hydrolysis reaction.

The acid groups corresponding to acids that are weaker than carbonate acidity, such as sulfur ions, hydrogen sulfide ions, metaaluminate ions, etc., can undergo a double hydrolysis reaction with aluminum ions in solution. Note: Sulfur ions, hydrogen sulfide ions, and iron ions mainly undergo redox reactions.

If two ions can undergo a double hydrolysis reaction in solution, they cannot be prepared in solution. If aluminum carbonate does not exist, aluminum sulfide is often prepared from aluminum and sulfur as raw materials, and cannot be prepared by metathesis reaction. The dihydrolysis reaction is a metathesis reaction, and the ion equation can be directly written by grasping the essence of the reaction, and it is easy to balance using the conservation of atoms and the conservation of charge.

For example, NaHCO3 is an example of dihydrolysis.

Double hydrolysis reactionThe definition (the double hydrolysis reaction) refers to a weak acidAnionand weak base cations promote hydrolysis with each other, such as trivalent aluminum ions andBicarbonateuntil a complete reaction is reached.

However, in fact, aluminum ions and bicarbonate do not necessarily undergo complete double hydrolysis, as long as the reaction conditions are slightly controlled, the coarse aluminum ions and bicarbonate can react to form basic alumina carbonate.

One of the conditions for a double hydrolysis reaction to occur is that the hydrolysate is easily detached from the solubility of the reaction system.

Very small substance. Of course, if the degree of hydrolysis is very large, the hydrolysis reaction can also be considered complete.

Principle

Because the solubility of Al(OH)3 is very small and H2CO3 is unstable and easy to decompose, the hydrolysate generated can be separated from the reaction system, and the hydrolysis reaction continues to the right according to the principle of equilibrium movement until the reaction is complete.

However, the solubility of Mg(OH)2 is larger than that of AL(OH)3, and it is not easy to break away from the reaction system, so the hydrolysis reaction will reach equilibrium to a certain extent, and the hydrolysis reaction cannot be carried out completely.

From the above, it is not difficult to see that the separation of the generated hydrolysate from the reaction system is an important reason for the chain bench for the complete reaction of the reaction. Therefore, one of the conditions for the "double hydrolysis reaction" to occur is:

Hydrolysates are substances that are easily separated from the reaction system (very low solubility), such as Al(OH)3, Fe(OH)3 or H2S, CO2 and other gases that can be dissolved in water. Of course, if the degree of hydrolysis is very large, the hydrolysis reaction can also be considered complete.

The above content reference: Encyclopedia - double hydrolysis.

In the case of complete hydrolysis, there is usually gas or precipitation in the hydrolysate products, resulting in irreversible hydrolysis reactions.

The double hydrolysis is that the two ions that make up the salt can be hydrolyzed, but not necessarily irreversible, such as the double hydrolysis of the ammonium carbonate of Liang Lao, but not completely hydrolyzed.

Completely hydrolyzed, it can be considered as special in double hydrolysis.

such as Al3+ and HCO-, until a complete reaction. Aluminum ions and bicarbonate do not necessarily undergo complete dihydrolysis, as long as the reaction conditions are slightly controlled, aluminum ions and bicarbonate can react to form basic alumina carbonate.

When two hydrolyzed and more acidic and alkaline solutions are mixed, they promote each other to carry out the hydrolysis reaction to the end. For example, the aqueous solution of aluminum sulfate is acidic, because Al3; ＋3ho≒al(oh)＋3h。The aqueous solution of sodium bicarbonate is alkaline because HCO+HO HCO+OH.

Conditions of the hydrolysis reaction:When ammonium chloride solution (NH+HO NHO+H) is mixed with sodium acetate solution (CHCOO Ho CHCOOH OH), the two salts are hydrolyzed and promote each other, and the hydrolysis trend increases, but Changchang is still very weak. Because the solubility of NHHO and CHCOOH, the products of NH hydrolysis, and CHCOOH, the hydrolysate products of NHoO, can still inhibit the hydrolysis of ammonium ions and acetate ions when the concentration of the hood reaches a certain limit, and it is resistant to stuffiness, so NH and CHCOO can still coexist in large quantities.

It can be seen that not all hydrolyzed acidic and hydrolyzed alkaline solutions will be mixed to undergo a double hydrolysis reaction. In general, the hydrolysate is easy to decompose, or the solubility is small, and double hydrolysis should be considered when mixing these two types of salt solutions. Within the scope of middle school chemistry textbooks, the ion pairs that can be dihydrolyzed are mainly as follows.

al3;with CO2; 、hco、s2;、hs、alo、sio2;；fe3;with CO2; 、hco、alo、sio2;；NH with ALO.

The above content** Encyclopedia - double hydrolysis.

Question 1: What are the chemical hydrolysis reactions in high schoolsHalogenated hydrocarbons are hydrolyzed in a strong alkaline aqueous solution, e.g., CH3CH2-Cl+H-OH NaOH

ch3ch2oh+hcl

Hydrolysis of sodium alkoxide, e.g.: CH3CH2ONa+H2O=CH3CH2OH+NaOH

Esters are hydrolyzed in aqueous solutions of acids and alkalis, such as: CH3COOCH2CH3+H2O H+OROH-CH3COOH+CH3CH2OH

Hydrolysis of disaccharides and polysaccharides, e.g. starch hydrolysis: (modulo C6H10O5) N+NH2O N6H12O6 (glucose).

Hydrolysis of dipeptides and peptides, e.g. H2NCH2CONHCH2COOH+H2O 2H2NCH2COOH

Hydrolysis of imine arch=n-ph (h20 h+) archo+phNH2

Question 2: What are the double hydrolysis anti-clearing types in high school? Only weak acids and weak alkali salts will be double hydrolyzed, as if the book says that this kind of situation does not need to be mastered.

The first floor is right, ammonium acetate is generally tested for double hydrolysis, and this double hydrolysis is generally not tested in the college entrance examination, because the textbook does not require mastery.

Double hydrolysis means that the yin and yang files that make up the salt can be hydrolyzed, and they promote each other in the reaction, so that the hydrolysis reaction is carried out to a deeper degree, and even tends to complete the rapid ridge or. For example, chlorine sulfide, the reason why it cannot exist in aqueous solution is that its double hydrolysis is completed, and it will become aluminum hydroxide and hydrogen sulfide when dissolved in water.

The essence of double hydrolysis is that the hydrogen ions and hydroxide ions produced by the hydrolysis of weak acid ions and weak alkali ions combine to make the hydrolysis continuous.

The hydrolysis reaction has the following characteristics:

1. This reaction is reversible, and the degree of hydrolysis is generally small.

2. The hydrolysis reaction is an endothermic reaction, so the temperature can promote the hydrolysis of salt.

3. Dilution can also promote hydrolysis.

Double hydrolysis means that the anions and cations that make up the salt can be hydrolyzed, and they promote each other in the reaction, so that the hydrolysis reaction is carried out to a deeper degree, and even tends to be completed by the old reed. For example, sulfur chlorine, the reason why it cannot exist in aqueous solution is that its double hydrolysis is completed, and it will become aluminum hydroxide and hydrogen sulfide when dissolved in water.

The essence of double hydrolysis is that the hydrogen ions produced by the hydrolysis of weak acid ions and weak base ions combine with hydroxide ions to make the hydrolysis continuous.

The hydrolysis reaction has the following characteristics:

1. This reaction is reversible, and the degree of hydrolysis is generally small.

2. The hydrolysis reaction is an endothermic reaction, so the temperature can promote the hydrolysis of salt.

3. Dilution can also promote hydrolysis.