What is the principle of strong acid to weak acid, and what is the principle of strong acid to weak

There are two cases:

1.Weak acids are not completely ionized in solution, and weak salts are hydrolyzed in solution. When the strong acid is added to the solution of the weak acid, the weak acid group will combine with the hydrogen ions ionized by the strong acid to form weak acid molecules, and the remaining cations of the weak acid will combine with the strong acid group to form the strong acid salt, so that the purpose of preparing part of the weak acid from the strong acid is achieved.

For example, adding hydrochloric acid to sodium acetate solution can partially produce sodium chloride and acetic acid.

2.Weak acids are unstable in solution and are easy to get out of the solution system. When the strong acid is added to the solution of the weak acid, the weak acid group combines with the hydrogen ions ionized by the strong acid to form weak acid molecules, which are unstable and easy to detach or decompose from the solution, so that the reaction between the strong acid and the weak acid continues, and this situation is reflected more thoroughly.

For example, dilute sulfuric acid is added to sodium carbonate solution, which can react violently to produce sodium sulfate, carbon dioxide and water.

Weak acids mainly exist in the molecular state, and strong acids mainly exist in the ionic state.

If the ions are combined to release energy (the formation of chemical bonds to release energy is a universal law), the overall energy can be reduced, if the energy is lower, the more stable the system, the easier it is to form, so there is a "strong acid to weak acid".

The strong acid is completely ionized, and the weak acid forms molecules, which can reduce the energy of the entire reaction system.

Strong acid means that acid dissolved in water can ionize into hydrogen ions and acid ions to a large extent, and weak acid is relative to strong acid, which refers to the partial ionization of acid in solution, and most of it exists in a molecular state in solution.

The general acid-to-acid reaction is actually a metathesis reaction, and whether this reaction can occur depends on the strength of the acid but also considers whether there is precipitation, gas, and the formation of high or low boiling point acids. For example, phosphoric acid (a moderately strong acid) is used to make Hi and HBR (both are stronger acids than hydrochloric acid). Although phosphoric acid is a weak acid, the reaction can occur due to the formation of gas.

For example, perchloric acid is formed by the reaction of sulfuric acid with barium perchlorate, although we say that perchloric acid is more acidic than sulfuric acid, but because of the formation of barium sulfate precipitation, the reaction can also occur. Therefore, we should understand it for strong acid to make weak acid, and do not simply classify it as strong acid to make weak acid when there is an acid and salt that reacts with salt to form another acid and salt.

Metathesis reactions of non-redox reactions:

Acidic acids with stronger acidity can produce less acidic acids because the degree of ionization of stronger acids in aqueous solution is greater than that of weaker acids, and the hydrogen ions produced by ionization can combine with the acid root ions of weaker acids to form weaker acid molecules that are difficult to ionize and "free" out of the system, resulting in the chemical equilibrium moving in the direction of generating weaker acids.

In fact, the reason why weak acids can produce strong acids is the same, that is, the whole reaction proceeds in the direction of decreasing the total ion concentration, but because the solubility of the resulting salts is really small. For example: CuSO4 + H2S = = Cus (precipitation) + H2SO4 and so on.

It refers to the reaction of strong acid with the salt of weak acid to form weak acid and strong salt, because weak acid is a weak electrolyte, and the tendency to bind hydrogen is stronger than that of strong acid.

Example: ch3coona

hcl=ch3cooh

NaCl, acetic acid (weak acid) and sodium chloride (strong salt) are reacted with hydrochloric acid (strong acid) and sodium acetate (weak salt).

Another example is caco3

2hno3=ca(no3)2

H2CO3, which is reacted with nitric acid (strong acid) and calcium carbonate (weak salt) to obtain carbonic acid (weak acid) and calcium nitrate (strong salt), and in middle school, it is believed that carbonic acid is directly decomposed after formation to obtain H2O

CO2 (gas): Under normal circumstances, weak acids cannot make strong acids.

Both are strong acids to weak acids.

But there are 3 situations to consider this possibility.

1.Produces substances that are insoluble in acids and water.

2.Redox occurs.

3.Strong acids have low boiling points and are volatile.

Here are a few more examples (which should still be available in high school).

h2scuso4=cus↓

2agno3=ag2s↓

pb(no3)2=pbs↓

2hno3

Hello! In general, only strong acids can be used to make weak acids, but this is only an empirical formula and not a theorem law, that is, there are special cases.

For example, H2S (weak acid) + CuCl2==Cus + 2HCl (strong acid), this is because of the formation of Cus insoluble substances, resulting in the occurrence of weak acids to strong acids

2HF+CACl2==CAF2 +2HCl (because: calcium fluoride precipitation is insoluble in dilute hydrochloric acid at room temperature).

And so on, (not to list them all.......)Too much will make you dizzy, hehe).

When you go to high school in the future, you will pay attention to it and slowly understand those special circumstances, it is not difficult.