Chemistry

This is a long answer type question as classified in NCERT Exemplar

The process of osmosis is of immense biological and industrial importance as is evident from the following examples:

A. Biological Importance :

(i) Osmosis is responsible for some of the water movement from the soil into the plant roots and then into the top parts of the plant.

(ii) Adding salt to meat to protect it against bacterial action (ie. salting).

(iii) Sugar is used to protect fruits from bacterial attack. Bacterium in canned fruit shrivels and dies as a result of the osmosis process.

(iv) Salt blood cells break due to osmosis when placed in water containing less than 0.9 percent (mass by volume). Osmosis causes water retention in tissue cells and intercellular gaps in those who consume a lot of salt or eat salty foods. Edema is the name given to the puffiness or swelling that results as a result of this.

(v) When withered flowers are immersed in freshwater, they revive.

B. Industrial importance

(i) For desalination of seawater, reverse osmosis is used: when a pressure greater than osmotic pressure is applied to saltwater, clean water is squeezed out through a semipermeable membrane. For this, a number of semipermeable membranes are available.

This is a long answer type question as classified in NCERT Exemplar

Raised increases in size when submerged in water. It's due to a phenomenon known as "Osmosis." The process is depicted graphically in figure. A semipermeable membrane separates a solution from its solvent in this procedure, allowing solvent molecules to pass through but preventing solute particles from passing through.

The passage of solvent molecules from a pure solvent to a solution via a semipermeable membrane is known as osmosis. The following are three osmosis applications:

(i) Osmosis is responsible for some of the water movement from the soil into the plant roots and then into the top parts of the plant.

(ii) Adding salt to meat to protect it from bacterial attack.

(iii) Adding sugar to fruits to protect them from bacterial attack. Bacterium in canned fruit shrivels and dies as a result of the osmosis process.

This is a long answer type question as classified in NCERT Exemplar

"Azeotropes” is the general term for binary mixes that deviate from Rault's law and whose components cannot be separated by fractional distillation. Because of the following reasons, fractional distillation cannot produce pure ethanol: Azeotropes are binary solutions (liquid mixes) with the same composition in the liquid and vapour phases, therefore fractional distillation cannot separate the components of an azeotrope. On fractional distillation, an ethanol-water mixture (obtained via sugar fermentation) yields a solution containing approximately 95 percent ethanol by volume of ethanol. Because the liquid and vapour phases have the identical composition, they cannot be separated. There are two sorts of binary mixtures that are referred to as-

(1) Minimum boiling azeotrope: At a given composition, non-ideal solutions show a considerable positive divergence from the minimal boiling azeotrope. For instance, 95 percent ethanol and 5% water (by volume): Below are the boiling points of pure ethanol, water, and its azeotrope. Ethanol has a melting point of 351.3 degrees Celsius, while water has a melting point of 373 degrees Celsius and azeotrope has a melting point of 351.1 degrees Celsius.

(2) Maximum boiling azeotrope: Non-ideal solutions with a considerable negative departure from Rault's law from the maximum boiling azeotrope at a given composition. By mass, nitric acid and water have a composition of 68 percent nitric acid and 32 percent water. The boiling point of such an azeotropic HNO₃-H₂O mixture is 393.5 K.

This is a long answer type question as classified in NCERT Exemplar

Ideal solution: The 'ideal solution' is a binary solution of two volatile liquids that follows Raoult's rule at any concentration and temperature.

Ideal solutions are formed when the intermolecular attractive forces between the solute (A) and the solvent (B) (ie.A-B interaction) are approximately equal to those between the solvent-solvent (A-A) and the solute-solute (BB). Enthalpy of mixing, mixing H=0, in such a perfect solution.

Volume change on mixing, Δ mixing V=0.

Examples: n- hexane and n-heptane.

Non ideal solution:  At any concentration and temperature, these binary solutions of two volatile liquids do not obey Raoult's law.

P_A≠P_oAx_A

P_B≠P_oBx_B

Furthermore, non-ideal solutions are formed when the intermolecular attractive forces between the solute and the solvent (A-B interaction) are not equal (either stronger or weaker) to those between the solvent and the solvent (A-A) and the solute and the solute (B-B). 

Enthalpy of mixing, ΔH is not equal to 0. & Volume change on mixing,   V is not equal to 0.

Example: CS₂ and acetone.

where, P_oA, P_oB denote the vapour pressures of pure solvent and PA, PB denote the partial vapour pressures of components A and B in solution, and X denotes the mole fractions of the two components denoted by the subscripts A and B.