Sec.1 | Aqueous Solutions and their Properties | Unit 1 - Lesson 4 | Integrated Sciences

شرح علوم متكاملة لغات الصف الاول الثانوي لغات - الفصل الدراسي الأول
شرح علوم متكاملة اولي ثانوي لغات - ترم أول
Integrated Sciences for Grade 10 (First Year of Secondary School) - First Semester

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in this Lesson:
The colligative properties of the solution: They are properties of the solution that depend on the number of ions or molecules of the non-volatile dissolved substance (solute), not on the type of the solute.

First: Lowering the vapor pressure
At a certain temperature, the volume of the liquid in an open container decreases over time, as a result of the evaporation of its molecules that are found on the liquid surface.
When a certain volume of the liquid is placed in a closed flask ( closed system) at a certain temperature, some of the liquid molecules are released from its surface and liberated as vapor molecules, while some of its vapor molecules return to the liquid, which is known as condensation.
When the rate of the liquid evaporation is equal to the rate of the vapor condensation, this leads to the constancy of each of the liquid and vapor amount, this is known as the liquid and its vapor are in a case of "dynamic equilibrium" .
The vapor formed above the liquid surface from the evaporation process causes pressure on the liquid surface, which is known by "the liquid vapor pressure"
Vapor pressure: It is the liquid vapor pressure on the liquid surface in a closed container, when the liquid and its vapor are in dynamic equilibrium at a constant temperature and pressure.

Dynamic equilibrium: It is an equilibrium between the evaporation rate of the liquid and the condensation rate of its vapor at constant temperature and pressure in a closed container.

▌The decrease in the vapor pressure of a solution is directly proportional to the number of solute molecules or ions dissolved in the solution.
As the number of molecules or ions in the solution increases, its vapor pressure decreases .
i.e. The relation between the vapor pressure of the solution and the number of solute molecules or ions is inversely proportional .

Boiling point of a liquid:
It is the temperature at which vapor pressure of the liquid is equal to the atmospheric pressure that exerted on the liquid surface.


The relation between the boiling point and the number of solute particles
When dissolving a non-volatile substance in pure water to form a solution, the vapor pressure
decreases, therefore the boiling point of the solution is higher than the boiling point of
solvent (pure water) forming it at standard atmospheric pressure, because the attraction forces
between the solute molecules and the solvent molecules or ions in the solution increase
the energy needed to evaporate the liquid.
The elevation in the boiling point of a solution is directly proportional to the number of
the dissolved substance molecules or ions in the solution.

Freezing point of the liquid: It is the temperature at which the substance is converted from the liquid state into solid state.

Osmosis: It is the phenomenon of transferring (movement) of water from the diluted solution to the concentrated solution through the semi-permeable membrane separating between the two solutions.

Osmotic pressure: It is the pressure that arises in the solution due to the difference in solutes concentration between two solutions, leading to the diffusion of water by osmosis from the low-concentrated solution (low osmotic pressure) to the high concentrated solution (high osmotic pressure) through the semi-permeable membrane.

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