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1 Jan 2012

SOLUTIONS (CHEMISTRY)


                                           SOLUTIONS

Dissolution   When a solid solute is added to the solvent, some solute dissloves and its concentration increases in solution. This prosess is known as dissolution.
Saturated solution:  such a solution in which no more solute is dissloved at the same temperature and pressure is called a saturated solution.
Unsaturated solution: such solution in which more solute can be dissloved at the same temperature and pressure.
Factors affecting solubility
1.    Nature of substance
2.    Effect of temperature
3.    Effect of pressure

                      
                 SOLUBILITY OF A GAS IN A SOLUTION

Oxygen dissloves only to the small extent in water. It is this dissloved oxygen which sustains all aquatic life. On the other hand hydrogen chloride is highly soluble in water.the solubility of gases increases with increase in pressure.

Henry was the first to give a quantative relationship between pressure and solubility of gases in the solvent which is known as henry law.

The law states that at a constant temperature the solubility of the gas in the liquid is directly proportional to the pressure of the gas.
Dalton, a contemporary of henry, also concluded independently that the solubility of gas in the liquid is the function of partial prussure of the gas.

The most commonly used  form of henry law states that “the partial preussure of the gas in the vapour phase (p) is directly proportional to the mole fraction of the gas in the solution.
                   P     =KhX

The solubility of gases increases with decrease in temperature. It is due to this reson the aquatic species sre more comfortable in cold waters rather  than in warm water.

Henry’s law find several application in industry and explain some biological phenolmena:

To increase the solubility of co2 in soft drinks and soda water , the bottle is sealed under high pressure.

Scuba divers must cope with high concentraction of dissolved gases while breathing air at high pressure under water.increased pressure increases the solubility of atmospheric gases in blood. When the diver cames towards surface, the pressure gradually decreases. This releases the dissolved gases and leads to the formation of bubbles of nitrogen in the blood. This blocks capillaries and creates a medical condition known as bend which are painful and dangerous to life. To avoid bend , as well as the toxic effect of high concentrations of nitrogen in the blood , the tanks used by scuba divers are filled with air diluted with helium.

At high altitude the partial pressure of oxygen is less than that of the ground level.this leads to low concentration of oxygen in the blood and tissues of people living living at high altitude or climbers.
Low blood oxygen causes climbers to became weak and unable to think clearly, symptoms of of a condition known as anoxia.

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