solution

[róng yè]

Homogeneous and stable dispersion system

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This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Two or more substances are mixed to form uniform and stable Dispersion system It's called a solution. Solutions can be liquid, gas or solid. For example, air is a gas solution, and solid solution mixture is often called Solid solution , such as alloy. Generally, compounds that can dissolve other substances are called solvent The dissolved substance is called solute 。 When gas or solid is dissolved in liquid, the liquid is called solvent, and the gas or solid is called solute. If two liquids dissolve each other, the one with more is called solvent, and the one with less is called solute.^[1]

Chinese name: solution
Type: mixture

Field: Chemistry
Nature: Uniform and stable

catalog

seven temperature variation
eight Correlation calculation

brief introduction

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Solution: A homogeneous and stable mixture of one or more substances dispersed in the form of molecules or ions in another substance.

Dispersant Particle diameter<1nm (1 × 10 -9 m) Of Dispersion system 。 Dispersions are molecules or ions with transparent, uniform and stable macroscopic characteristics.

Press Aggregate state Different classifications:

Gaseous solution : Gas mixture, referred to as gas (such as air).

Liquid solution : Dissolution of gas or solid in liquid or liquid-liquid phase, referred to as solution (such as brine).

Solid solution : Solid mixture with molecular dispersion Solid solution (such as alloy).

Pronunciation: It is generally read as "so and so（ solute ）Of（ solvent ）Solution ", such as hydrogen peroxide solution It can be called the aqueous solution of hydrogen peroxide.

Note: If the solvent is water, it can be referred to as a solution, for example, "aqueous solution of ethanol" can be called Ethanol solution 。

If the two liquids are mutually soluble, water shall be used as the solvent if there is water, otherwise the solvent with high quality shall be used.

Solution properties

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1. Homogeneity: the density, composition and properties of the solution are identical everywhere;

2. Stability: the solute and solvent will not separate (transparent) for a long time when the temperature and solvent amount are constant;

3 Mixture: The solution must be a mixture.^[2]

Solution classification

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Saturated solution : A solution in which the solute cannot be dissolved in a certain amount of solvent at a certain temperature.

Unsaturated solution : A solution in which the solute can continue to be dissolved in a certain amount of solvent at a certain temperature.

Mutual conversion of saturated and unsaturated solutions:

Unsaturated solution can be solved by increasing solute (applicable to all solutions) or reducing temperature (applicable to most solutes whose solubility increases with temperature, otherwise, the temperature must be increased, such as Limewater ）Evaporated solvent (when the solvent is liquid) can be converted into saturated solution.

Saturated solution can be converted into unsaturated solution by increasing solvent (applicable to all solutions) or increasing temperature (applicable to most solutes whose solubility increases with temperature, and vice versa, reducing temperature, such as lime water).

Regular solution Is closer Actual solution A solution of. Its formation is consistent with that of ideal solution except that the entropy of mixing is not equal to zero. Thermodynamic law derived from regular solution, widely used in Non electrolyte Solution, especially for the application of many alloy solutions, is more suitable. Therefore, for metallurgy and metal material science Solution theory It is very important.

Composition

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1. Solute: dissolved substance (for example, salt and water are used to prepare brine, and salt is solute)

2. Solvent: a substance that can dissolve other substances (for example, salt and water are used to prepare brine, and water is the solvent)

3. When two liquids are mutually soluble, the more one is called solvent, and the less one is called solute.

4. When two liquids are mutually soluble, if one of them is water, water is generally called solvent.

5. Solid or gas is dissolved in liquid, usually called solvent.

Solution preparation

Wherein, water (H two O) It is the most commonly used solvent and can dissolve many substances. Gasoline, alcohol and chloroform are also commonly used solvents, such as gasoline can dissolve grease, alcohol can dissolve iodine, and so on.

solute Dissolve in solvent to form solution, and the curve of solubility change of substance is called Solubility curve 。 The solubility curve can find out the solubility of a substance at a certain temperature.

The solubility of a gas refers to the volume of the gas when it is dissolved in a volume and reaches saturation at a pressure of 1 standard atmospheric pressure and a certain temperature.

Solid solubility It indicates the mass of a substance dissolved when it reaches saturation in 100g solvent at a certain temperature. The solubility of most solids increases with the increase of temperature, but the solubility of a few solids decreases with the increase of temperature.

formation mechanism

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The process of solution formation is accompanied by changes in energy, volume and sometimes color. Dissolution is a special physical and chemical change, which is divided into two processes. One is the dispersion of solute molecules or ions, which requires heat absorption to overcome the attraction between molecules and increase the volume; The second is the combination of solvent molecules and solute molecules, which is an exothermic process and reduces the volume at the same time. The overall situation of the whole process is the joint effect of two aspects.^[3]

Solution use

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The chemical reaction in solution is usually faster. Therefore, in the laboratory or chemical production, to make two reactive solids react, they are often dissolved first, then the two solutions are mixed and shaken or stirred to speed up the reaction.

The solution is also of great significance to the physiological activities of animals and plants. When animals ingest nutrients in food, they must digest them and turn them into solutions before they can absorb them. In animals, oxygen and carbon dioxide are also dissolved in the blood for circulation. The glucose solution and normal saline used in medical treatment, the injection for curing various inflammation caused by bacterial infection (such as gentamicin and kanamycin), and various eye drops are all prepared according to certain requirements. Plants obtain all kinds of nutrients from the soil, and must become a solution to be absorbed by the roots. The soil contains water, which dissolves a variety of substances to form a soil solution, which contains nutrients needed by plants. Many fertilizers, such as human excrement, cattle and horse dung, crop straw, weeds, etc., must undergo a process of decomposition before application. One of the purposes is to make complex insoluble organic substances into simple soluble substances, which can be dissolved in soil solution for crops to absorb.

temperature variation

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Material dissolution, on the one hand, is the particle of solute - molecules or ions need to overcome their mutual attraction to leave the solute, on the other hand, the dissolved solute needs to diffuse to the whole solvent, these processes need to consume energy, so when the substance dissolves, it needs to absorb heat. This is why the temperature drops during dissolution.

If the dissolution process is simply diffusion, it should be all endothermic. Why is there any exothermic? It turns out that in the process of dissolution, solute particles molecules or ions not only need to be separated from each other and dispersed into the solvent, but also solute particles dissolved in the solvent can also form solvates with solvent molecules (if the solvent is water, then hydrate ）。 Heat is released in this process.^[2]

Correlation calculation

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The calculation is based on the constant total amount of solute before and after dilution. It can be calculated whether water is used or dilute solution is used to dilute the concentrated solution.

(1) Dilute the concentrated solution with water

Set the mass of concentrated solution before dilution as m , the mass fraction of solute is a %, the mass of water added during dilution is n , the mass fraction of solute after dilution is b %。

Then we can get m × a %=( m + n )× b %。

(2) Dilute the concentrated solution with dilute solution

Set the mass of concentrated solution as A , the mass fraction of solute is a %, the mass of dilute solution is B , the mass fraction of solute is b %, the mass fraction of solute after mixing the two solutions is c %。