What are the knowledge points of chemical solution in the third year of junior high school?

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The knowledge points of chemical solutions in the third year of junior high school are summarized as follows:

1. Solution concept: one or several substances are dispersed into another substance to form a uniform and stable mixture.

2. Solution characteristics: uniformity and stability.

3. Solution composition:

Solute: A substance that is dissolved, which can be solid, liquid, or gaseous.

Solvent: A substance that dissolves other substances. Water is the most commonly used solvent, and gasoline, alcohol, etc. can also be used as solvents.

4. Dissolve the solution.

1) Endothermic: After some substances are dissolved in water, the temperature of the solution decreases during the whole process, such as NH4NO3 (or ammonium nitrate) solids.

2) Exothermic: After some substances are dissolved in water, the temperature of the solution increases during the whole process, such as NaOH solids and concentrated H2SO4.

3) Absorption and exothermic are not obvious: After most substances are dissolved in water, the temperature of the solution does not change significantly in the whole process, such as NaCl solid.

5. Solution emulsification: detergent and other emulsifiers can make vegetable oil disperse into countless fine droplets in water, without gathering into large oil beads, so that oil and water are no longer stratified, and the stability of the formed emulsion is enhanced, this phenomenon is called emulsification, and the emulsification effect of detergent is used to clean the oil stains on the tableware.

<>Formation of solutions

1. Solution. (1) The concept of solution: a homogeneous and stable mixture formed by the dispersion of one or several substances into another substance is called a solution.

2) The basic characteristics of the solution: uniformity and stability.

Note: a. The solution is not necessarily colorless (e.g., CuSO4 is blue; Feso4 solution is light green; Fe2(SO4)3 solution is yellow);

b. The solute can be solid, liquid or gaseous; Water is the most commonly used solvent;

c. The quality of the solution = the quality of the solute + the quality of the solvent; The volume of the solution ≠ the volume of the solute + the volume of the solvent;

d. Name of the solution: solvent solution of solute (e.g., iodine wine - alcohol solution of iodine).

Composition: solute and solvent, solute can be many, solvent can only be one.

Judgment of solutes and solvents:

The liquid state is a solvent, and the solid or gaseous state is a solute;

When they are in a liquid state, the amount is more solvent, and the less amount is solute;

When there is water, the water must be a solvent, and the others are solutes;

When you don't know how much it is, you can use the name - the solvent solution of the solute, the front is the solute, and the back is the solvent.

It is formed by dispersion of small insoluble droplets into a liquid. The mixture is called an emulsion.

The phenomenon that two liquids that cannot be mixed together due to the action of surfactants is called emulsification, and surfactants that have an emulsifying effect are called emulsifiers.

The mixture formed by the suspension of small solid particles in a liquid is called a suspension.

Saturated solution, unsaturated solution

1) Concept: At a certain temperature, a certain solute is added to a certain amount of solvent, and when the solute can not continue to dissolve, the resulting solution is called the saturated solution of this solute, and the solution that can continue to be dissolved is called the unsaturated solution of this solute.

2) Judgment method: continue to add the solute to see if it can continue to dissolve.

3) Conversion between saturated and unsaturated solutions

4) The relationship between concentrated and dilute solutions and saturated unsaturated solutions

A saturated solution is not necessarily a concentrated solution;

An unsaturated solution is not necessarily a dilute solution, such as a saturated aqueous solution of lime is a dilute solution;

At a certain temperature, the saturated solution of the same solute is denser than its unsaturated solution.

Exothermic and endothermic phenomena during dissolution

The process of dissolution: a. diffusion endothermy; b. Hydration and exothermy; Together, these two processes determine whether the dissolution is endothermic or exothermic; Dissolution endothermy: such as NH4NO3 dissolution;

Dissolution and exothermy: such as NaOH dissolution, concentrated H2SO4 dissolution; Dissolves without obvious thermal phenomena: such as NaCl.

Part of the content includes saturated solution, unsaturated solution, solubility content, conceptual things are more, when we should pay attention to grasp the characteristics of the concept, pay attention to understand the connotation of the concept, such as the definition of solution to grasp: even.

1. Stability and mixture; When conceptualizing, we should also pay attention to the comparison of similar concepts, such as saturated solutions and unsaturated solutions, it is better to understand them by comparison.

1. Judgment of solution: judge according to the characteristics of the solution (uniformity and stability).

Homogeneity: refers to the fact that the solute concentration and properties of all parts of the solution are the same. However, after the molecules or ions dispersed in the solvent in the solution reach a uniform state, they are still in a state of irregular motion.

Stability: When the external conditions (temperature, pressure, etc.) remain unchanged, the solution will not stratify for a long time, and will not precipitate solids or gases.

2. Judgment of solvent and solute

One or several substances are dispersed into another substance to form a homogeneous, stable mixture, called a solution; The dissolved substance is called a solute; Substances that can dissolve other substances are called solvents.

The following points should be paid attention to in the understanding of the solution:

The solute can be solid, liquid, or gas before it is dispersed.

The solution is not necessarily colorless, and its color is determined by the properties of the solute and solvent.

Water is the most commonly used solvent, and substances such as alcohol (ethanol) and gasoline can also be used as solvents. When a variety of liquids form a solution, the largest amount is the solvent, and the rest is the solute, but when there is water in the solution, no matter how much water there is, it is customary to regard water as a solvent; Solvent solutions are not usually specified, but are generally aqueous solutions.

3. The use of the solution.

Many reactions take place in solution, which can speed up the rate of the reaction.

The solution is of great significance to the physiological activities of animals, plants and people. The nutrients in the food ingested by animals must be digested and turned into a solution before they can be absorbed; Plants get all kinds of nutrients from the soil, which also need to be turned into a solution so that they can be absorbed by the roots.

4. Endothermic and exothermic substances when dissolved:

The process by which the solute is dispersed into a solvent to form a solution is called dissolution of a substance. In the process of dissolving a substance to form a solution, the process of diffusion of the molecules (or ions) of the solute into the solvent absorbs heat, and the process of the molecules (or ions) of the solute reacts with the solvent to form a solvent complex releases heat, so the dissolution of the substance is usually accompanied by a change in heat.

Diffusion endothermic Hydration exothermic – the temperature of the solution decreases.

Heat of dissolution phenomenon Diffusion endothermy Exothermic hydration – the temperature of the solution does not change.

Diffusion endothermic hydration exothermic – an increase in the temperature of the solution.

4. Application of crystallization: Crystallization is often used to purify substances.

5. Judgment of emulsification phenomenon:

Emulsification means that after the emulsifier is added, the emulsion (a mixture of oil and water) does not stratify but can be stably separated, and can become fine droplets that flow away with the water. This is the reason why the grease stains on clothes and tableware can be washed off with water with detergent. Emulsification is not dissolution and cannot form a solution.