Chemsafe tutorial

Created by AKHILESH TIWARI

It is used to calculate kf of solvent . ΔvapH is latent heat of fussion .

• R = 0.0821 liter·atm/mol·K
• R = 8.314 J/mol·K for SI UNIT
• R = 8.2057 m ·atm/mol·K
3

• ∆ H = Letent heat of vapourisation

• Anti-freeze solutions – ethylene glycol + water or glycerene + water

• Freezing mixture : ice + common salt
OSMOSIS : the spontaneous flow of solvent molecules through semipermeable membrane from a pure
solvent to a solution or from a dilute to a concentrated solution.
(osmosis given by Abbe Nollet (1748)
Difference between Osmosis and Diffusion :
Diffusion Osmosis
(i) In diffusion, solute as well as solvent the flow of solvent molecules occurs in one
molecules flow in opposite directions direction only.
semipermeable membrane* is not required semipermeable membrane* is required

Semipermeable membrane - "A membrane which allows only solvent molecules to pass through it.
Exp. Parchment paper, membranes covering the animal and plant cells , Egg membrane, goat's bladder (
natural) , parchment .
And calcium phosphate and copper ferrocyanide (, C U 2[Fe(CN)6]) ., cellophane.

Osmotic pressure - the hydrostatic pressure built up on the solution which just stops the osmosis.
Or , The external pressure which must be applied on the solution in order to stop the flow of the solvent
into the solution through semipermeable membrane is equal to 0smotic pressure.

Π = hdg
Π = CRT
𝑛
= 𝑉 𝑅𝑇
Π𝑉 = 𝑛𝑅𝑇
= hdg := AeRT
osmotic pressure is proportional to relative lowering of vapour pressure

HYPOTONIC SOLUTION - A solution of low osmotic pressure is termed hypotonic.

HYPERTONIC SOLUTION - solution of high osmotic pressure is termed hypertonic.
- osmosis takes place from hypotonic to hypertonic because solvent concentration is greater in hypotonic
solution.
Chemsafe tutorial
Created by AKHILESH TIWARI

ISOTONIC SOLUTIONS: Solutions having the same osmotic pressures at given temperature are termed
isotonic.
- Such solutions have equal molarity .

• two solutions of same substance having different osmotic pressures

• Osmotic pressure of the mixture of two different substances-

(𝑖1𝑛1+𝑖2𝑛2)
𝜋= 𝑅𝑇
𝑉1+𝑉2

• To calculate molecular mass - S or R May be used.

.Edema : There will be an escape of water and solute into the interstitial space resulting in
interstitial edema (swelling) whenever the hydrostatic pressure is much higher than the osmotic
pressure inside the intravascular space.

• Plasmolysis: contraction of the protoplast of a plant cell as a result of loss of water from the cell BY exo
osmosis.

• Some biological explanation on the basis of osmosis are given below: . '
(i) In animals, circulation of water to all parts of the body takes place due to osmosis. . .
(ii) Plant roots absorb water from soil due to osmosis. The concentration of cell sap inside the root hair cells is
higher than that of water present in the soil. Water enters the root cells due to endosmosis.
(iii) Water absorbed by plant roots is circulated in the entire plant body and reaches to the top of a tall tree due to
osmosis.
(iv) Osmosis helps in plant growth and germination of seeds.
(v) Red blood cells burst when placed in water; it is due to endosmosis.
(vi) Various functions of plants are controlled by osmosis, e.g., Stretching of leaves and flowers, opening and closing
of flowers.
Chemsafe tutorial
Created by AKHILESH TIWARI

(vii) Use of salt and sugar in pickles and jams acts as preservatives. It prevents growth of bacteria and fungi by
osmosis.
(viii) Dead bodies swell under water due to endosmosis.
(ix) When dried fruits and vegetables are placed in water, they slowly swell and return to their original form. It is
again due to endosmosis of water into the fruits and vegetables. '.

Note: (i) A 0.91% solution of NaCI in water is isotonic to human blood. Hence, in this solution red blood cells neither
swell nor shrink.
(ii) Aqueous solution of NaCI with concentration less than 0.91 % is hypotonic to blood. On placing red blood cells in
this solution, endosmosis results in bursting of RBCs.
(iii) Aqueous solution of NaCI with concentration more than 0.91 % is hypertonic to blood. Placing red blood cells in
it exosmosis or plasmolysis results in shrinking of cells.

Reverse osmosis: . If external pressure greater than osmotic pressure is applied, the flow of solvent
molecules flows from solution to pure solvent, i.e in reverse direction. This is called reverse osmosis.
: Reverse osmosis occurs when a
pressure larger than the osmotic
pressure is applied to the solution.

• Cellulose acetate is used which is permeable to water but impermeable to impurities and ions present in sea
water.
• Reverse osmosis is used for the desalination of sea water for getting fresh drinking water.
• RO to purify water in homes.
Advantage:
• used to determine molar masses of proteins and polymers.
• particularly useful for biomolecules as they are generally not stable at higher temperatures and polymers
have poor solubility.
• The osmotic pressure method has the advantage over other methods Because-
1. Measurment is possible at room temperature to avoid decomposition or freezing.
2. the molarity of the solution is used instead of molality
3. Magnitude is large for dilute solution also.

Abnoramal molar mass:-

A molar mass that is either lower or higher than the expected or normal value is called as abnormal molar
mass.
Reason: - 1. association of solute particles
2. Dissociation of solute particles.

Abnormal colligative properties - the colligative properties due to dissociation or association of solute
particles is called abnormal colligative properties.
𝐴𝑏𝑛𝑜𝑟𝑚𝑎𝑙 𝑣𝑎𝑙𝑢𝑒 𝑜𝑓𝑐𝑜𝑙𝑙𝑖𝑔𝑎𝑡𝑖𝑣𝑒 𝑝𝑟𝑜𝑝𝑒𝑟𝑡𝑦 ∝ 𝑁𝑜. 𝑜𝑓𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠 𝑜𝑓𝑠𝑜𝑙𝑢𝑡𝑒 𝑎𝑓𝑡𝑒𝑟 𝑖𝑜𝑛𝑖𝑠𝑎𝑡𝑖𝑜𝑛 𝑜𝑟 𝑎𝑠𝑠𝑜𝑐𝑖𝑎𝑡𝑖𝑜𝑛
Van’t hoff factors - it is extent of dissociation or association of solute.
(𝑛𝑜𝑟𝑚𝑎𝑙 𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠)
𝑖 =
𝐴𝑏𝑛𝑜𝑟𝑚𝑎𝑙𝑚𝑜𝑙𝑎𝑟𝑚𝑎𝑠𝑠
Chemsafe tutorial
Created by AKHILESH TIWARI

(𝑂𝑏𝑠𝑒𝑟𝑣𝑒𝑑 𝑐𝑜𝑙𝑙𝑖𝑔𝑎𝑡𝑖𝑣𝑒 𝑝𝑟𝑜𝑝𝑒𝑟𝑡𝑦)

𝑖 =
(𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒𝑑 𝑐𝑜𝑙𝑙𝑖𝑔𝑎𝑡𝑖𝑣𝑒 𝑝𝑟𝑜𝑝𝑒𝑟𝑡𝑦)
(𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓𝑚𝑜𝑙𝑒𝑠 𝑜𝑓𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠 𝑎𝑓𝑡𝑒𝑟 𝑎𝑠𝑠𝑜𝑐𝑖𝑎𝑡𝑖𝑜𝑛/𝑑𝑖𝑠𝑠𝑜𝑐𝑖𝑎𝑡𝑖𝑜𝑛)
𝑖 =
(𝑁𝑢𝑚𝑏𝑒𝑟𝑜𝑓𝑚𝑜𝑙𝑒𝑠𝑜𝑓𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠 𝑏𝑒𝑓𝑜𝑟𝑒 𝑎𝑠𝑠𝑜𝑐𝑖𝑎𝑡𝑖𝑜𝑛/𝑑𝑖𝑠𝑠𝑜𝑐𝑖𝑎𝑡𝑖𝑜𝑛)

i > 1 for dissociation.

i < 1 for association.

• Degree of dissociation -
n = ions on dissociation '
'alpha is its degree of ionization
(𝑖−1)𝑛
- Degree of association - 𝛼 = 1−𝑛
n is no. Of particles associated as unit.

- Acetic acid being associated and form dimers when dissolve in benzene. (i less than zero) and dissociated
when dissolve in wate( i more than 1).
-