important notes with easy concept class 12th cbse unit 2 solution .for more videos subscribe my you tube channel sk knowledge point

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SK KNOWLEDGE POINT
Part – 1
BY:SANJAY SIR

2. The classification of matter

3. What are Solutions?
• When two or more than two substances mix and form
a uniform or homogeneous mixtures, such a mixture is
called solution.
• By homogenous mixture we mean that its composition
and properties are uniform throughout the mixture.
• Generally, the component that is present in the largest
quantity is known as solvent. Solvent determines the
physical state in which solution exists. One or more
components present in the solution other than solvent
are called solutes.

4. What are Solutions?
• In a homogeneous mixture the diameter of the
molecular particle is 10-9 meter.
• In a homogeneous mixture the different components
can be separated by physical methods like filtration,
sedimentation, boiling or centrifugation etc.
• Solution is formed when solute and solvent molecules
experience attractive interaction between them. For
example, there is a strong attractive interaction
between molecules of ethanol and water, therefore
ethanol is soluble in water and forms a solution. But
there is negligible attraction between the molecules of
benzene and water, therefore benzene remains
insoluble in water and no solution is formed.

5. Types of Solutions
• The solutions can be found in three states; Solid, Liquid
and Gas. The solute and solvent can also be in three
states. The physical state of the resulting solution can
be decided on the basis of the physical states of solvent
and solute.

6. Characteristics of Solutions
• Solution can be formed if the solute or solvent has the
following characteristics
i. If the number of –OH groups in organic compound is more
in a solute, it is more soluble in water. More is the number
of –OH groups, more is the solubility. For example Glycerol
is more soluble in water than Ethanol.
ii. Most of the polar solutes dissolves in polar solvents. e.g.
HCl in water.
iii. Most of the non-polar solutes dissolves in non-polar
solvents. e.g. Naphthalene in benzene
iv. Most of the ionic solutes are soluble in water because they
are ionic even in solid state. e.g. NaCl in water.

7. Characteristics of Solutions
• If water is solvent in the solution, the solution is known
as an aqueous solution. (Aqua means water)
• If the water is not the solvent, the solution is known as
non-aqueous solution.
• In a non-aqueous solution, generally benzene, ether,
carbon tetrachloride etc. are used as non-aqueous
solvents.

8. Units of Concentration
• Composition of a solution can described bybe
The quantitativeexpressing
proportion
its concentration.
of solute and solvent are different in
different solutions.
• The amount (quantity) of solute in unit volume of
solution or unit weight of solvent is called
concentration of solution.
• There are different ways to express concentrations of
solutions. Normality, Molarity, Formality, Molality, Mole
fraction, Weight fraction (% W/W) etc. are some units
of concentration.

9. Formality
• Ionic compounds are in ionic form even in solid state
and not in molecular form. Hence formula mass is
taken instead of molecular mass and the concentration
is known as formality.
• The sum of atomic masses of the atom, in the
proportion formula of the compound is called its
formula mass. e.g. compounds like potash alum, the
molecular formula is K2SO4.Al2(SO4)3.24H2O hence it’s
molecular mass will be 948 grams.mole-1. The
proportion formula of alum is KAl(SO4)2.12H2O so the
value of its proportion formula mass is 474 gram
formula mass.

10. Formality
• At normal temperature, if one gram formula mass of
the solute is dissolved in one liter of solution, it is
called one formal solution and it’s formality is one. This
type of concentration is called formality. It is indicated
by the symbol F.

11. Formality

12. Volume percentage (% V/V)
• The volume (ml) of solute dissolved in 100 ml of solution is
expressed as Volume percentage (% V/V). Such solution is called
percent, proportion with reference to the volume of solute.
• For example, 10% ethanol solution in water means that 10 mL of
ethanol is dissolved in water such that the total volume of the
solution is 100 mL. Solutions containing liquids are commonly
expressed in this unit. For example, a 35% (v/v) solution of
ethylene glycol, an antifreeze, is used in cars for cooling the
engine.

13. Volume percentage (% V/V)

14. Mass by Volume percentage (% W/V)
• The mass of solute dissolved in 100 mL of solution is
called mass by Volume percentage (% W/V). Such
solution is called percent mass, proportion with
reference to the mass of solute.
• For example, 5% W/V aqueous solution of sugar
means 5 grams of sugar is dissolved in 100 mL of
solution.
• This unit of concentration is commonly used in fields of
medicine and pharmacy.

15. Mass by Volume percentage (% W/V)

16. Parts per million (p.p.m.)
the amount of solute present in the• Sometimes
solution is in very less (trace) quantities. In such
conditions, the concentration is expressed as Parts per
million (ppm).
• For example, the amount of oxygen dissolved in sea
water, amount of pollutants in air and water etc. are
expressed using this unit.
• Parts per million can be expressed in three different
ways, parts per million mass to mass, parts per million
mass to volume and parts per million volume to
volume.

17. Parts per million mass to volume
• Parts per million mass to volume is the amount in milligrams of
solute dissolved in one liter of solution.
• So the unit of Parts per million mass to volume can be written as
mg liter-1 and also as microgrammL-1.
• Now if we express the amount of solute in grams and volume of
solution in mL then;

18. Parts per million mass to volume

19. Molarity
• Molarity: Molarity (M) is defined as number of moles
of solute dissolved in one litre (or one cubic
decimetre) of solution
• For example, 0.25 mol L–1 (or 0.25 M) solution of
NaOH means that 0.25 mol of NaOH has been
dissolved in one litre (or one cubic decimetre).

20. Molality
• Molality: Molality (m) is defined as the number of
moles of the solute per kilogram (kg) of the solvent
and is expressed
• For example, 1.00 mol kg–1 (or 1.00 m) solution of
KCl means that 1 mol (74.5 g) of KCl is dissolved in 1
kg of water.

21. Mole fraction
• Mole fraction: Commonly used symbol for mole
fraction is x and subscript used on the right hand side
of x denotes the component. It is defined as:
• For example, in a binary mixture, if the number of
moles of A and B are nA and nB respectively, the
mole fraction of A will be

22. Solubility
• Solubility of a substance is its maximum amount that
can be dissolved in a specified amount of solvent. It
depends upon the nature of solute and solvent as well
as temperature and pressure.

23. Solubility of Gases ( Solubility of Gaseous
solute in Liquid solvent)
• Many gases dissolve in water. Oxygen dissolves only to
a small extent in water. It is this dissolved oxygen which
sustains all aquatic life. On the other hand, hydrogen
chloride gas (HCl) is highly soluble in water.
• Factors which affect the Solubility of Gaseous solute
dissolved in Liquid solvent to from a homogeneous
solution are:
i. Nature of the gaseous solute and solvent
ii. Effect of temperature
iii. Effect of pressure

24. Nature of the gaseous solute and
solvent
• The solubility of gases like O2, N2 H2 etc. is less in water
but more in ethyl alcohol.
• Also, the solubility of gaseous solutes like H2S, NH3 etc.
is more in water as compared to their solubility in ethyl
alcohol.
• So, the solubility depends upon the nature of gaseous
solute and also the nature of solvent.

25. Effect of temperature
• The solubility of gaseous solute dissolved in a liquid
solvent decrease with increase in temperature.
• With increase in temperature, the gaseous solute
dissolved in a solution bubbles out and hence the
solubility of a dissolved gas decreases with increase in
temperature.
• Such an effect can also be explained by Le-Chatelier
principle of equilibrium as under:

26. Effect of pressure
• The solubility of gases increase with increase of
pressure. For solution of gases in a solvent, consider a
system as shown in figure (a). The lower part is solution
and the upper part is gaseous system at pressure p and
temperature T. Assume this system to be in a state of
dynamic equilibrium, i.e., under these conditions rate
of gaseous particles entering and leaving the solution
phase is the same. Now increase the pressure over the
solution phase by compressing the gas to a smaller
volume [Fig. 2.1 (b)].

27. Effect of pressure
• This will increase the number of gaseous particles per unit
volume over the solution and also the rate at which the gaseous
particles are striking the surface of solution to enter it. The
solubility of the gas will increase until a new equilibrium is
reached resulting in an increase in the pressure of a gas above
the solution and thus its solubility increases.

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