CBSE class 12 ncert chemistry download pdf: Free Chemistry chapter-2 'Solution' fast track revesion notes.

CBSE class 12 Ncert chemistry download pdf: Free Chemistry chapter-1 'Solution' fast track revesion notes.

    Chapter - 2   Solution

1.A solution is a homogeneous mixture of two or more substances whose composition can be varied within certain limits.

2.Expression of concentration Composition of a solution can be described by expressing its concentration.

Several ways to describe the concentration of the solution quantitatively are as follows:

● Percentage by mass (w/w)=

Mass of the component in the solution /Total mass of the solution x 100

● Percentage by volume (V/V)

(Volume of the component/ Total volume of   solution)×100

● Mass by volume percentage (w/v) is the mass of solute dissolved in 100 mL of the solution.

●  Parts per million (ppm) =

(Number of parts of the component÷ Total number of parts of all components of the solution  )×10⁶                                                       

●Mole fraction (x) is the ratio of number of moles of one component to the total number of moles of all the components present in the solution.

Mole fraction of solute,

X(solute) = n (solute)/ n(solute)+n(solvent)

It is independent of temperature.

For given solution, sum of mole fraction of all the component of a solution is unity, i.e.

X1 +X2+........Xi=1

●Molarity (M) is defined as the number of moles of solute dissolve in one litre or one cubic decimate of the solution. 

                     Molarity = Moles of solute/Mass of                                                                 solvent (in kg)

 ● Molality (m) is defined as the number of moles of the solute per kilogram of the solvent.

    

        Molality = moles of solute/mass of solvent                                                                              (in kg)

•Molality,mole fraction, mass fraction ,etc. are preffered over Molarity, normality,etc. because they are temperature independent.

3.Solubility of a substance is its maximum amount that can be dissolved ( in a specified amount of solvent ) at a specified temperature. It depends upon the nature of solute and solvent at a specified temperature and pressure.

4. Solubility of a solid in a liquid When a solid solute is added to the solvent, some solute dissolves and its concentration increases in solution. This process is known as dissolution. Some solute particles in solution collide with solid solute particles and get separatd out of solution. This process is known as crystallisation.

5.Henry's law  states that the partial ptessure of the gas (p) is proportional to the mole fraction of the gas( χ) in the solution. 

Mathematically, it is expressed as

           p∝χ  or p=kₕχ 

 where , Kₕ is called Henry's law constant.

• Higher the value of Kₕ, at a particular temperature, lower is the solubility of the gas in the liquid.

• Solubility of gas decreases with increase in temperature. This is the reason that aquatic species are more comfortable in cold water rather than in warm water.

6. The pressure exerted by the vapours above the liquid surface in equilibrium with the liquid at a given temperature is called vapour pressure.

7. Raoult's law states that at a given temperature, for a solution of volatile liquids, the partial vapour pressure of each component of the solution is directly proportional to its mole fraction present in solution, i.e. p₁∝χ₁ and p₁ = p₁°χ₁

For a solution of two miscible components, 1 and 2,

 Pₜₒₜₐₗ= P₁ +P₂ = p°₁ χ₁ + P₂° χ₂

As we know, χ₁ + χ₂ = 1or χ₁=1-χ₂

 Pₜₒₜₐₗ = P₁+ (P₂°-P₁°)χ₂

8.  Solutions obeying Raoult's law over an entire range of concentration are called ideal solutions and those do not obey this law are called non-ideal solutions.

     For positive deviation,

    A-B interaction< A-A or B-B interactions

    e.g. CS₂+ acetone, acetone +benzene

   For negative deviation,

    A-B interaction A-A or B-B interactions e.g.        chloroform + acetone, chloroform +

    benzene.

9. Azeotropes are binary mixtures having same composition in liquid and vapour phase and boil at constant temperature. There are two types of azeotropes which are:

• Minimum boiling azeotropes These solutions show positive deviation from Raoult's law, e.g. ethanol-water mixture.

• Maximum boiling azeotropes These solutions show large negative deviation from Raoult's law, e.g. nitric acid-water mixture.

10. The properties of solutions which depend only on the number of solute particles, not on the nature of the solute particles are known as colligative properties.

These properties are as follows:

• Relative lowering of vapour pressure in an ideal solution containing the non-volatile solute is equal to tge mole fraction of the solute at a given temprature.

χ₂= Δp₁/p₁°= (p₁°-p₁)/p°₁= W₂M₁/W₁M₂

here, component number(1) is solvent and component number (2) is solute ,W₁andW₂ are the masses and M₁ and M₂ are the molar masses of the solvent and solute, respectively.

•Elevatolion of boiling point (ΔTᵇ)(Ebullioscopy)

    is the difference in the boiling points of the solution (Tᵇ) and( Tᵇ°)

 It depends upon the number of solute particles rather than on their nature.

•Depression in freezing point(ΔTᶠ) (Cryoscopic) is the decrease in the freezing point of solution when non volatile solute is dissolve in it.

•Osmosis is a process which involves the flow of solvent molecules through a semipermeable mambrane from pure solvent to the solution and  osmotic pressure of the solution (π) is the pressure that just stops the flow of solvent.

π=CRT 

π=W₂RT/VM₂

(C = Molarity)

11. Isotonic solutions are the solutions having same osmotic pressure at a given temperature. In case of two solutions of different osmotic pressures, the solution with higher osmotic pressure is called hypertonic solution and that with lower osmotic pressure is called hypotonic solution.

12. Phenomena on the basis of osmosis People taking a lot of salt or salty food experience water retention in tissue cells and intercellular spaces because of osmosis. This resulting puffiness or swelling is called edema.

13. In reverse osmosis, the solvent flows from solution side towards pure solvent, if external pressure is higher than osmotic pressure applied on solution side. It is used for desalination of sea water. Solvent moves from solution to pure solvent side.

14. Some Important Facts

• Intramolecular H-bonding lowers boiling point.

 • Benzoic acid and acetic acid dimerises in benzene.

• When egg is kept in saturated salt solution after

removing the hard shell using dil, HCl, egg will

shrink due to osmosis.

• CaCl2 acts as a non-volatile solute and results depression in freezing point. Thus, snow is reduced (as it melts) and prevents blocking of roads in cold region.

•Ethylene glycol is mixed with radiator water to decrease the freezing point of water in cold region.

• Camphor is used for molecular mass determination due to its volatile nature.

• To increase the solubility of CO2 in soft drinks, the bottle is sealed under high pressure.

• Helium-oxygen mixture is used by deep sea divers because of its low solubility in blood.