# CBSE Class 12 Chemistry Solutions Board Exam Notes

SOLUTION is the homogeneous mixture of two or more than two components. Most of the solutions are binary i.e. consists of two components out of which that is present in the largest quantity is called solvent & one which is present in smaller quantity called solute.

EXPRESSING CONCENTRATIONS OF SOLUTIONS

¶ Mass percentage: Mass of solute per 100g of solution Mass % = (mass of solute / total mass of solution) X 100
¶  Volume percentage : volume of solute per 100ml of solution Volume % = (volume of solute/ total volume of solution) X 100

¶  Parts per million: parts of a component per million (106) parts of the solution.
ppm = no. o f parts of the component / total no. of parts of all components of the sol. X 106
¶  Mole fraction(x): It is the ratio of no. of moles of one component to the total no. of all the components present in the solution . For binary solution :‐ the no. of moles of A and B are nA and nB respectively
so, xA= nA/nA+nB ; xB= nB/ nA+nB
In binary solution xA+ xB= 1
¶  Molarity: No. of moles of solute dissolved in one litre of solution .
Molarity(M) = moles of solute/ vol. of solution in litre
¶  Molality(m) : No. of moles of solute per kg of the solvent.
Molality(m) = moles of solute/mass of solvent in kg
Molality is independent of temp. whereas molarity is a function of temp. because vol. depends on temp. and mass does not.

HENRY'S LAW

It states that at a constant temp. the solubility of the gas in liquid is directly proportional to the pressure of the gas above the surface of the liquid .
It also states that the partial pressure (p) of a gas in vapour phase is proportional to the mole fraction of the gas (x) in the solution.
P=KHX
KH is Henry's law constant .

APPLICATION OF HENRY'S LAW

¶  To increase the solubility of CO2 in soda water and soft drinks the bottle is sealed under high pressure.
¶  To avoid bends , toxic effects of high concentration of nitrogen in the blood the tanks used Used by scuba divers are filled with air diluted with He.

RAOULT'S LAW :‐ it states that :
1) For a solution of volatile liquid , the partial vapour pressure of each component of the solution is directly proportional to its mole fraction present in solution.
PA= P0
A XA PB= PB XB
The total pressure is equal to sum of partial pressure. Ptotal= PA+ PB
2) For a solution containing non‐volatile solute the vapour pressure of the solution is directly proportional to the mole fraction of the solvent.

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