شرح درس
Solutions
CHEMISTRY - Secondary 1
In This part we will study
Dissolving process
* Although water seems to be static in the beaker, but its molecules really in a continuous motion, especially the surface molecules (due to their kinetic energy).

Dissolving ionic compounds and polar compounds in a polar solvent.
It's easy to dissolve :
- Ionic compound (as sodium chloride).
- Polar covalent compound (as hydrogen chloride gas).
Dissolving process: Is the process that occurs when the solute decomposes or dissociates into negative and positive ions or into separated polar molecules. Each of them binds to the molecules of the solvent.
Example: Dissolving of sodium chloride in water:
 The polar water molecules collide with the crystals of NaCl by their kinetic energy.

 Water molecules attract Na+ and Cl- ions by directing the suitable pole towards them to be separated from NaCl crystal.

 Water molecules which surround the ions isolate positive ions from negative ions and prevent their binding again.

The speed of the dissolving process depends on:
 Surface area of the solute.  The stirring process.  Temperature.
Solubility

Solubility : It is the amount of solute in grams, which dissolves in 100 g of solvent to form
a saturated solution at standard temperature and pressure (STP).

Factors affecting the solubility
 The nature of solvent and solute
"Like dissolves like" is a well-known statement which controls the solubility process, this statement can be explained as follows:


Application :
Solubility of some substances in polar and nonpolar solvents:
 Oil is insoluble in water. (G.R)
Because water is a polar solvent and oil is a nonpolar compound so, oil doesn't dissolve in water.

 Oil is soluble in benzene. (G.R)
Because oil (non polar substance) is dispersed between molecules of benzene (nonpolar solvent) due to the weak bonds between the benzene molecules.

 Sugar is soluble in water, although sugar is a nonpolar substance. (G.R)
Because water molecules form hydrogen bonds with sugar molecules, sugar molecules contain polar hydroxyl groups (OH-) as shown in the figure.




 Effect of temperature on solubility
Observe the opposite diagram which shows the solubility of several salts as a function of temperature.
There are three cases:
 The solubility of most salts increases greatly by increasing the temperature, such as NaNO3 , KNO3 , KCl and KClO3

 The solubility of some salts increases slightly by increasing the temperature, such as NaCl

 The solubility of some salts decreases by increasing the temperature, such as Ce2(SO4)3


Solubility of gases in water differs from that of salts, where the solubility of gases decreases by increasing temperature
(as shown in the opposite figure).


Example
 Which substance that its solubility increases with decreasing the temperature?

 What is •the difference in mass of KNO3 which is dissolved in a saturated solution of it, when heated from 20°C to 40°C ?

 Calculate the required mass of KCl for dissolving in 200 g of water to form a saturated solution at 80°C

 Calculate the mass of the precipitated KC1O3 after cooling a saturated solution of it, from 70°C to 30°C

Best wishes to you
Mr.Ahmed Elbasha

كيمياء الصف الاول الثانوي لغات - الفصل الدراسي الاول
شرح كيمياء لغات اولي ثانوي - مستر احمد الباشا
كيمياء لغات - الصف الاول الثانوي - كيمياء اولي ثانوي الترم الاول - كيمستري اولي ثانوي الترم الاول