Why is it wrong to say that there must be a chemical change due to precipitation 20

The phenomenon of precipitation is a physical phenomenon, which can be caused by a change in physical conditions, or it may be a phenomenon caused by a change in the physical conditions of a substance caused by a change in chemical reaction, or a phenomenon caused by a change in the physical conditions of the reaction environment, or a chemical change may occur but no change in the physical conditions to cause precipitation. The cause of precipitation is directly related to the solubility of the substance, and the concentration of solutes in the solvent exceeds the solubility to produce precipitation. (There are also dissolved substances adsorbed with each other; Pester; The volume of the solute increases due to physical reactions such as adhesion, or other solutes crowd out the dissolution space of the solute and form a precipitate) and the solubility is affected by the temperature; Pressure; interference with other solutes; Affected by many factors such as pH, one or several factors may produce precipitation due to changes in conditions, so it is wrong to say that "precipitation must produce chemical changes".

There is not necessarily a chemical change caused by precipitation, such as the precipitation of calcium hydroxide after the aqueous solution of calcium hydroxide is heated, the change is a physical change, not a chemical change, so it is wrong.

Chemical change, also known as chemical reaction, is essentially characterized by the formation of new substances, and the process of chemical change is accompanied by physical change.

Physical change, i.e., no change in the formation of new matter. (Physical change is simply a change in the shape and state of the substance).

Sediment is insoluble and precipitated when placed in water, which is a physical change.

It could also be a physical change.

For example, alum water purification is the adsorption of aluminum hydroxide, and the sedimentation of colloids, which are all physical changes, and small particles combine into large particles to form a precipitate.

Do you understand saturated solutions? Lowering the temperature (most of them can do this) has precipitation, this is because it can't be dissolved, basically too little water, and it's also physical.

Ca(OH)2 saturated solution After cooling, Ca(OH)2 is precipitated, and the change is transformed into physical change.

1. The solubility of the substance, after forming a saturated solution, it will be precipitated if it cannot be dissolved.

2. Colloidal aggregation and precipitation, small particles become large particles.

Heating the clarified lime water, because the solubility of Ca(OH)2 decreases with increasing temperature, and heating will precipitate Ca(OH)2

The water freezes and forms a solid, but with a physical change.

Muddy water.

Colloidal aggregation and precipitation.

Heating the clarified lime water, because the solubility of Ca(OH)2 decreases with increasing temperature, and heating will precipitate Ca(OH)2

The water freezes and forms a solid, but with a physical change.

You can heat some substances whose solubility decreases with the increase of temperature, or the easiest way is to evaporate the brine, as soon as you evaporate, the water in the brine will disappear, and the salt in it will precipitate, which is a physical change, not a chemical change, because no new substances are produced in the process of change!

Not necessarily. The premise of chemical change is the creation of new substances. When no new substance is formed, it is not a chemical change.

The key to precipitation depends on when it occurs, and it can also be a physical change, for example, when the brine solution is evaporated, when the solvent is burned to a certain extent, there will also be sodium chloride precipitation, which is also a kind of precipitation, but this is a physical change process.

Chemical change refers to the process of conversion or transfer of atoms or electrons between molecules in contact with each other to form new molecules accompanied by changes in energy, which is essentially the breaking of old bonds and the formation of new bonds.

Chemical changes are always accompanied by physical changes. In the process of chemical change, there are usually luminescence, exothermia, and endothermy. According to the atomic collision theory, the chemical change between molecules is accomplished through collision, and two conditions need to be met to complete the collision of the molecule that reacts

1) Have sufficient energy; (2) Correct orientation. Because the reaction needs to overcome a certain molecular energy barrier, it must have a higher energy to overcome the molecular energy barrier. Two colliding molecules must have the correct orientation for the old bond to break.

Lime water reacts with CO2: Ca(OH)2 + CO2 ==CaCO3 + H2O

Sulfuric acid and barium chloride solution reaction: H2SO4 + BACL2 ==BaSO4 +2HCl

Sodium hydroxide with copper sulfate: 2NaOH + CuSO4 ==Cu(OH)2 + Na2SO4

Sodium hydroxide with ferric chloride: 3NaOH + FeCl3 ==Fe(OH)3 + 3NaCl

Sodium hydroxide with magnesium chloride: 2NaOH + MgCl2 ==Mg(OH)2 + 2NaCl

Sodium hydroxide with copper chloride: 2NaOH + CuCl2 ==Cu(OH)2 + 2NaCl

Calcium hydroxide with sodium carbonate: Ca(OH)2 + Na2CO3 ==CaCO3 + 2NaOH

Sodium chloride solution and silver nitrate solution: NaCl + Agno3 ==AgCl + Nano3

Sodium sulfate and fiber-searched barium chloride: Na2SO4 + BACL2 ==BaSO4 leaky wax + 2NaCl

1.Precipitate precipitation means: adding chemical agents to the solution to convert the soluble substances in the solution into insoluble substances, so as to precipitate in the solution and precipitate at the bottom of the solution.

2.The methods of precipitation and precipitation are: insoluble salt precipitation method, which refers to the method of precipitation and precipitation of some components in the form of insoluble compounds.

3.It can be used for component separation, impurity removal or extraction.

4.The insoluble salt precipitation method is divided into three types: precipitant precipitation method, concentrated crystallization method and salting out crystallization method.

If the substance itself is insoluble, then if it is placed in water, it will precipitate due to its insolvency – this is not a chemical change. For example, calcium carbonate powder is placed in water;

If the substance itself can be dissolved in water, but the amount of water is small, and the amount of powder is large, because a saturated solution has been formed, the added solute cannot be completely dissolved, and there is an undissolved solute in the saturated solution, resulting in precipitation - this is not a chemical change; If a large amount of NaCl is dissolved in a small amount of water;

If two or more substances that are soluble in water are dissolved in excess of water, a precipitate is produced, which is different from the original solute and is a new precipitate – this change is a chemical change. If BaCl2 and Agno3 are dissolved in excess water, AGCL precipitation will occur.

Therefore, the precipitation phenomenon is not necessarily a chemical change, and the judgment of whether there is a chemical change depends on the solubility of the added substance, the amount of water added, and the nature of the added substance (to see whether the two can undergo chemical changes to obtain a substance that is insoluble in water).

Of course, if precipitation is encountered in the inference of matter, in many cases it is caused by chemical changes, and it depends on the environment and specific description set in the specific topic.

If you have any questions, please ask, I hope it can help you.

Your question should be answered from two aspects. 1. All changes generated by precipitation are chemical changes, and attention should be paid to the formation of precipitation. Second, there is a precipitation phenomenon is not necessarily a chemical change, for example:

Saturated lime water, when the temperature is raised, will precipitate, not a chemical change.

Not necessarily, some solutions will precipitate when solutes are added after saturation, and some will precipitate crystals.

Precipitation is a unit operation in which the target product or major impurities in the solution are precipitated in the form of an amorphous solid phase and then separated. Precipitation methods include isoelectric point precipitation, salting out method, organic solvent precipitation method, etc.

The process of producing a separable solid phase from the liquid phase, or an insoluble substance precipitated from a supersaturated solution. Precipitation indicates the process of formation of a new condensed phase, or the process of deposition due to the addition of a precipitant that makes certain ions insoluble compounds. The chemical reaction that produces the precipitation is called the precipitation reaction.

Hello, precipitation is actually a solid substance that exceeds the solubility and is not dissolved.

Substances such as BaSO4 and CaCO3, due to their low solubility, dissolve very little after being dissolved in water, and most of them are not dissolved or solid, which is precipitate.

Hope it helps.

In chemistry, solid substances that are insoluble in water are basically precipitates, such as silver chloride, barium sulfate, etc

Junior high school: no precipitation in acid.

Sodium, potassium, barium, ammonia, and calcium are slightly soluble in alkali.

In salt: potassium, sodium, ammonium, nitrate are dissolved.

Silver hydrochloride is insoluble.

Barium sulfate is insoluble, calcium and silver are slightly soluble.

Carbonate dissolves only potassium and sodium ammonium.

Ask your former chemistry teacher.

Physical change.

Physical changeGenerally speaking, the composition of matter itself does not change. For example, changes in plate position, volume, shape weight, temperature, pressure, and conversion between gaseous, liquid, and solid states.

There are also the interaction between matter and electromagnetic fields, the interaction between light and matter, and the interaction and transformation between microscopic particles (electrons, atomic nuclei, elementary particles, etc.), all of which are physical changes.

In fact, the fundamental difference between physical change and chemical change is that no new matter is formed during physical change, while chemical change (for example, the process of copper forming patina is chemical change).

It depends on the cause of the precipitation. For example, the precipitation caused by the decrease in the temperature and solubility of the solution is a physical change; Because the substances in the solution react with each other to form new substances and produce a precipitate, that is a chemical change.