Why increase the concentration of salt solution and reduce the degree of hydrolysis

You can consider an extreme case where the salt concentration tends to infinity, which is equivalent to a pure salt solid, and the solid is not hydrolyzed, that is, the degree of hydrolysis is 0. That is to say, in the process from small concentration to very large concentration, the degree of hydrolysis tends to 0, so the concentration of salt solution.

Increase and decrease the degree of hydrolysis.

Specific analyses require the use of hydrolysis constants.

If the subject has learned the hydrolysis constant, you can derive it in the following way:

The hydrolysis constant is a fixed value at a constant temperature, so if you are in the denominator.

Multiply by a constant n(n>1), then you need to multiply n numerator as well. Because hydrolysis is generally beneficial to hydrogen ions and hydroxide ions in solution.

The effect of concentration is much greater than that of ionization of water, so the n on the molecule can be assigned to two terms, each assigned the root number n. Because n>1, it is easy to get the root number n from mathematical knowledge is also greater than 1, so the increase in the denominator is greater than the increase in the terms of non-hydrogen ions and hydroxide ions on the molecule, so that the degree of hydrolysis is reduced.

Purely conceptual question!

The degree of hydrolysis is related to the concentration of the solution, and the concentration of the hydrolyzed product is the concentration of solutes.

It can be approximated as the degree of hydrolysis.

The hallmark of the hydrolytic equilibrium shift is the magnitude of the forward and reverse reaction rates.

See, as the concentration of the salt solution increases, the concentration of reactants increases, and the rate of positive reaction naturally accelerates, and the equilibrium shifts, but at the same time, the concentration of solutes rises (solutes are added), resulting in a larger denominator of the degree of hydrolysis, and although the concentration of hydrolyzed products also increases, the degree of hydrolysis still decreases.

As a vivid example, nitrogen and hydrogen to ammonia, now that you increase the concentration of nitrogen, the equilibrium is obviously moving in a positive direction; However, because there is too much nitrogen and not enough hydrogen, the increase in ammonia is far less than the increase in nitrogen, that is, the conversion rate of nitrogen is reduced.

Categories: Education, Science, >> Learning Aid.

Problem description: Salt hydrolysis, external causes: why salt hydrolysis weak ion concentration is smaller and easier to hydrolyze.

Analysis: The hydrolysis of salts is a chemical equilibrium, according to the principle of equilibrium movement (Lechatre's principle), the thinner the solution, that is, the more water there is, the equilibrium will move in the direction of hydrolysis. Therefore, the smaller the concentration of salt hydrolysis, the easier it is to hydrolyze.

For example, nitrate cress imitation cave silver solution is the following balance:

agno(3)+h(2)o agoh+hno(3)The more water there is, the more water shifts the equilibrium to the right, that is, the smaller the concentration of salt hydrolysis, the more it is easy to hydrolyze.

The more dilute the more hydrolyzed the explanation is as follows:

In the hydrolysis of inorganic salts, the factors that affect the hydrolysis are the concentration of salts, temperature, and acidity. That is, the smaller the concentration of salt, the greater the degree of hydrolysis it has. The thinner, that is, the smaller the concentration, the greater the degree of hydrolysis.

Taking the hydrolysis of weak acid and strong alkali salt as an example, the hydrolysis equation is as follows:

In the reaction, when the amount of H2O increases, the concentration of CH3COOH on the right decreases more than the decrease in CH3COOH-, so the reaction proceeds to the right.

1. Definition of hydrolysis:Hydrolysis is a reaction in which ions ionized by salt combine hydrogen ions ionized from water and hydroxide ions to form weak electrolyte molecules.

2. Types of inorganic substances that occur in hydrolysis:Strong acid and weak alkali salt, strong alkali weak salt, weak acid and weak alkali salt.

3. Hydrolytic equilibrium constant:The hydrolysis constant is the amount that indicates the degree of hydrolysis.

The above content reference: Encyclopedia - Hydrolysis.

Encyclopedia - Hydrolytic equilibrium constant.

Taking strong acid and weak alkali salt copper sulfate as an example, copper sulfate is the product of the neutralization of strong acid sulfuric acid and weak alkali copper hydroxide, so the cationic divalent copper ion in the copper sulfate solution is hydrolyzed with water to generate copper hydroxide precipitation and sulfuric acid. The greater the concentration of copper sulfate solution, the smaller the pH of the solution, and the greater the acidity, so it can inhibit the degree of hydrolysis. The smaller the concentration of copper sulfate solution, that is, diluted with water, the closer the pH of the solution is to neutrality, the greater the degree of hydrolysis.

The principle of the degree of hydrolysis: the pH of the solution determines the degree of hydrolysis. For example, the hydrolysis of strong acid and weak alkali salts, the addition of acid reduces the pH and maintains the acidity of the solution, the hydrolysis is inhibited, and the dilution of water or the addition of alkali increases the pH promotes hydrolysis.

The hydrolysis of weak acids and strong alkali salts (such as sodium sulfide) is the opposite of the hydrolysis of strong acids and weak alkali salts, and the addition of alkali can inhibit hydrolysis, and the addition of acid or water dilution promotes hydrolysis.

Hehe, classmates don't know if your teacher taught you a principle called self-sacrifice.

The first problem is explained in this way, when you increase the salt concentration, the equilibrium does shift to the right. But the degree of hydrolysis refers to the conversion rate. The principle of self-sacrifice means that when salt itself is added to the equilibrium, the reaction will shift to the right, but the conversion rate of itself will decrease, and the conversion rate of another substance will increase (the latter sentence is used in ordinary chemical equilibrium, there are two reactants, this is not the case in hydrolysis, of course, the other substance in hydrolysis refers to hydrogen ions or hydroxide ions).

If you think about it logically, you can understand that hydrolysis is very tiny after all, and if you add 1mol down, there will be one thousandth of the hydrolysis. Do you say that the conversion rate is decreasing or rising?

So you should also figure out the second question, you can write a hydrolysis equation casually. It's all about what kind of root ions react with water to produce something. If there is more water, the reaction will move to the right, and if there is more water, the conversion rate of oneself will decrease, and the conversion rate of the root ion will increase, and the degree of hydrolysis will increase.

Diluted with water, the chance of collision between ions is greatly reduced, so it will promote the hydrolysis of salts. But the degree of volume increase is much greater than the amount of ions produced by hydrolysis. So the concentration of ions produced by hydrolysis is reduced.

Why the thinner the more hydrolyzed.

Salt dissolves in water, which is a dissolution process, which is a physical change, and dissolution can be divided into two processes, the first is the diffusion process, which is a physical process. The second is the hydration process, which is a chemical process (not a chemical change).

Table salt is a physical process in the dissolution of substances, Na ions and Cl ions leave the solid surface of NaCl and diffuse into solvent water, thus forming a uniform liquid phase. This can be referred to as dissolving.

The dissolution of table salt in water is an ionization process, and there is a break of ionic bonds, which will release heat. Sucrose dissolution is a process of dilution and dispersion, and the sucrose molecule exists as a whole and will not break, but it is just a process of molecular dilution or dispersion in water.

At first, it will slowly dissolve, and the more it is added, it will reach saturation, and then it will not be dissolved, and if it is heated, it can dissolve a part, and there will be salt crystals precipitated after it cools. Because the solubility of water to table salt increases with the increase of temperature, but there is a certain limit, and its solubility decreases when the temperature decreases.

The volume of water does not grow larger.

What gets bigger is the volume of the solution of salt and water. And the magnitude of the increase is very small, because there are voids between the water molecules, and the salt molecules will dissolve into the voids of the water molecules.

The dissolution of table salt in water is not a chemical change, it is a physical change, and no new substances are formed. Table salt is soluble in water and ionized into sodium ions and chloride ions, but there is no new chemical bond to produce a feast. Evaporate the solution to still get table salt.