Throw points! Big Throw!! What is the dependence of a solution? Hurry, hurry!!

The formal definition is that the values of the vapor pressure drop, freezing point decrease, boiling point and osmotic pressure of the solvent in a dilute solution are only related to the amount of solute in the solution, and have nothing to do with the nature of the solute, so these properties are called the dependence of the dilute solution.

We all know that the general quantity of chemical substances is expressed in moles, one mole is so much, but when it comes to the quantity, it means that it is very thin, but according to the number, it also shows that there is a very small amount of things related, when the number is still in a small range, the quantity increases a little more, and the physical properties of the solution change, that is, the vapor pressure drops, the freezing point decreases, the boiling point rises, and so on!

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An ideal dilute solution is considered to be a solution with an infinitesimal solute concentration.

But even so, the presence of refractory solutes can affect the properties of the solution.

"Dependence" can be understood as the dependence on the nature of the data with solutes.

The most typical and commonly used is the change of melting and boiling point.

You've read the material, and the vagueness is certain, and this is the content of undergraduate physical chemistry.

You may be very interested in chemistry and have seen a few of them, but even then you can't reach the level of undergraduate comprehension, otherwise the chemistry department will be a dry meal.

The dependence of the solution, simply put, is that with the change of the quality of the solute in the solution, some properties of the solution are changed, or some parameters are changed, the common ones are the freezing point decreases, the boiling point increases, the osmotic pressure increases, the vapor pressure decreases, etc.

The dependence of dilute solution means that some properties of the solution are related to the number of particles of the solute, and have nothing to do with the nature of the solute. The dependency is quantitatively described by Raoult's law, boiling point increase, freezing point decrease and osmotic pressure formula.

As the name suggests, "dependence" is a nature that depends on quantity. The values of the vapor pressure drop, freezing point decrease, boiling point and osmotic pressure of the solvent in the dilute solution are all related to the amount of solute contained in the dilute solution, and these properties are called the dependence of the dilute solution.

1.Vapor pressure drops.

For a two-component dilute solution, the vapor pressure of the solvent decreases as described in Eq. (2-67).

p＝p*a－pa＝p*axb

That is, the value of δp is proportional to the number of solutes - the molar fraction of the solute xb, and the proportionality factor is the saturated vapor pressure p*a of pure a.

2.The freezing point (when a solid pure solvent is precipitated) is reduced.

When a dilute solution is cooled to the freezing point, it may precipitate a pure solvent, or it may be a solvent that precipitates with the solute. When only the pure solvent is precipitated, that is, the freezing point tf of the dilute solution in equilibrium with the solid pure solvent is lower than that of the pure solvent at the same pressure, and the experimental results show that the value of the freezing point reduction is proportional to the number of solutes contained in the dilute solution, and the proportional coefficient kf is called the freezing point decline coefficient, which is related to the solvent properties and has nothing to do with the solute properties. Detailed derivation.

3.The boiling point rises.

The boiling point is the temperature at which the vapor pressure p of a liquid or solution is equal to the external pressure pex. If the solute is not volatile, the vapor pressure of the solution is equal to the vapor pressure p pa of the solvent, and the vapor pressure curve of the dilute solution p*axa, pa p*a, so the vapor pressure curve of the dilute solution on the p-t diagram is below the vapor pressure curve of the pure solvent, and it can be seen from the figure that when the external pressure is pex, the boiling point tb of the solution must be greater than that of the pure solvent and the boiling point tb of the pure solvent must be greater than the boiling point t*b of the pure solvent, that is, the boiling point increases. The experimental results show that the boiling point of the dilute solution containing non-volatile solutes can also be deduced by thermodynamic methods, and kb is called the boiling point increase coefficient.

It is related to the nature of the solvent and not to the solute nature.

4.Osmotic pressure.

If a dilute solution is separated from a solvent by a semipermeable membrane in a U-shaped tube, the membrane allows the solvent but not the solute to pass through.

The experimental results show that a large amount of solvent will enter the solution through the membrane, so that the liquid level of the solution will continue to rise, until the equilibrium can be reached when the two liquid levels reach a considerable height difference. To make the height difference between the two liquid levels not occur, additional pressure can be applied on the liquid surface of the solution, assuming that at a certain temperature, when the pressure is applied on the liquid surface of the solution, the two liquid levels can maintain the same level for a long time, that is, to achieve osmotic equilibrium, this value is called the osmotic pressure of the solution. According to the experiment, the osmotic pressure of the dilute solution is proportional to the concentration of solute B, Cb, and the value of the proportionality coefficient is RT, i.e.

cbrt（2-99）

Osmosis and reverse osmosis are very important in biology. It also has important applications in seawater desalination technology.

The values of the vapor pressure drop, freezing point decrease, boiling point and osmotic pressure of the solvent in the solution are only related to the amount of solute in the solution, and have nothing to do with the nature of the solute, so these properties are called the dependence of dilute solution. Compared with pure solvents, dilute solutions have some physical properties such as a decrease in vapor pressure (the vapor pressure of a pure solvent increases with a rise in temperature, as does a dilute solution, but its vapor pressure is always lower than that of a pure solvent), a decrease in freezing point, an increase in boiling point, and osmotic pressure. Concentrated solution and electrolyte solution are not dependent The force of electrolyte solution and concentrated solution is relatively large.

For example, electrolytes are electrostatic forces between ions. This leads to a serious deviation from the ideal situation. Therefore, there is a difference between the dependence and the calculated value.

But it still has a dependence. It's just that electrolytes are more dependent than non-electrolytes. According to the textbook, the dependence of the electrolyte solution is greater than the value of the same concentration of non-electrolyte.

It is not pointed out that there is no dependence.

The boiling point rises, the freezing point decreases, the osmotic pressure changes, these properties in a dilute solution after specifying the type and quantity of solvents, these properties depend only on the number of molecules, and this property, which has nothing to do with the nature of the solute, becomes a dependent.

The result of dissolution is a change in some properties of the solute and solvent, and these changes in properties (i.e., solution properties) can be summarized into two categories: one is determined by the nature of the solute, such as density, color, conductivity, acidity and alkalinity, etc.

The other type of properties is determined by the number of solute particles, such as the vapor pressure of the solution drops, the boiling point increases, the freezing point drops and the osmotic pressure, especially in non-electrolyte dilute solutions, these properties have nothing to do with the nature of the solute, but only with the number of solutes.

Regardless of the properties of the solution itself, the boiling point rises, the freezing point decreases, the vapor pressure decreases, and the osmotic pressure changes by changing the percentage of the solute in the solution. For example, if sodium chloride is added to the sodium chloride solution and continues to dissolve, the above phenomenon will occur.

Supplement, to put it simply, is to change the number of particles in the solution, causing the boiling point to rise, the freezing point to decrease, the vapor pressure to decrease, and the osmotic pressure to change these phenomena. In other words, if the solution causes these phenomena, it depends on the change in the number of solute particles (referred to as dependence). These changes have nothing to do with the properties of the solution itself.

You can refer to a university textbook on inorganic chemistry or physical chemistry.

The dependence of dilute solution is generally reflected in four aspects: vapor pressure decreases, freezing point decreases, boiling point increases, and osmotic pressure changes.

Vapor pressure decrease MB = wb * ma * p saturated vapor pressure wa * vapour pressure decrease value.

The freezing point decreases MB=KF*WB DT*WA, and the boiling point increases as above.

Osmotic pressure = CBRT MB...

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cNo matter whether the freezing point of the solution decreases or the boiling point rises, it is because the saturated vapor pressure of the solution decreases. Because solutes are difficult to volatile, the volatility of the solution is lower than that of water, and the saturated vapor pressure becomes smaller. When the external pressure is constant, there must be a higher temperature to increase the saturated vapor pressure of the solution to ensure that the saturated vapor pressure is equal to the external pressure, that is, the boiling point.

In the same way, the drop in freezing point is also caused by a drop in vapor pressure.

The concentration of the solution is relative. For example. 25% sodium chloride is a concentrated solution relative to 10% sodium chloride. For a 35% sodium chloride solution, it is a dilute solution.

The relative molecular mass of solutes can be determined by using the dependence of dilute solutions.

Dependence of dilute solutions.

At a certain temperature and pressure, when a non-volatile solute is dissolved into a solvent to form a dilute solution, the saturated vapor pressure of the solution is lower than that of the pure solvent, the boiling point of the solution is higher than that of the pure solvent, the freezing point of the solution is lower than the freezing point of the pure solvent, and the osmotic pressure between the pure solvent and the solution is generated.

The difference between the vapor pressure, the freezing point, the boiling point, and the osmotic pressure of the dilute solution is only related to the concentration of solute particles contained in the solution, but not to the properties of the solute itself, so they are called the virtual luck of the dilute solution.