Chemistry NCERT Exemplar Solutions Class 12th Chapter Two

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

The fleeing tendencies of water molecules from the liquid level/surface create vapour pressure in any solvent or water. Only water molecules are present at the surface of pure water, but when a nonvolatile solute such as glucose is dissolved in it, a certain number of nonvolatile glucose molecules with no escape tendency are also present at the aqueous solution's surface.

As a result, the quantity of water molecules near the surface decreases, resulting in a lower number of water molecules being able to escape as vapours. When compared to pure water/solvent, this lowers the vapour pressure of water in its glucose solution. Its colligative feature refers to this relative decrease in vapour pressure. 

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

 (a) (i) According to Henry's law, a gas's pressure is proportional to its solubility. The air pressure gradually falls as scuba divers approach the surface. This lower pressure causes the dissolved gases in the blood to be released, resulting in the development of nitrogen bubbles in the blood. This causes capillaries to constrict, resulting in bends, a painful and life-threatening medical condition.

(ii) The partial pressure of oxygen at high altitude is lower than at ground level. People living at high altitudes have reduced oxygen concentrations in their blood and tissues as a result of this. Low blood oxygen causes weakness and discomfort.

(b)When a room-temperature soda water bottle is opened to the air, the partial pressure of CO₂ above the solution drops dramatically (as per Henry's law). As a result, the solubility of carbon dioxide decreases, causing CO₂ bubbles to fizz out of the bottle.

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

The number of moles of solute dissolved in one litre of solution is the molarity of a solution, which is defined as "the number of moles of solute dissolved in one litre of solution." Because volume is affected by temperature and changes with it, the molarity will also change as the temperature changes.

Other concentration words, such as mass percentage, ppm, mole fraction, and molality, are based on the mass-to-mass relationship of the solute and solvent in a binary solution. Because mass does not vary as a function of temperature, these concentration terms do not change as a function of temperature. The mass of the solvent used to make the solution is connected to the mass of the solute, according to the definitions of all of these words.

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

When dissolved in suitable solvents, certain solutes/compounds either dissociate or associate. For instance, ethanoic acid dimerises in benzene due to hydrogen bonding, but dissociates and produces ions in water.

As a result, the number of chemical species in solution rises or falls in relation to the number of chemical species of solute used to create the solution. Because the magnitude of the colligative property is dependent on the number of solute particles in relation to the total number of particles in solution, it is expected that the molar mass calculated using colligative properties will be either higher or lower than the expected or normal value, and this is referred to as abnormal molar mass.

Van't Hoff established a factor called the Van't Hoff factor to account for the degree of dissociation or association of molecules in solution. It can be summed up as follows:

The predicted colligative qualities are achieved by assuming that the nonvolatile solute is neither associated nor dissociated, and anomalous molar mass is the empirically determined molar mass. The value of I (van't Hoff factor) is smaller than unity in the event of association, but greater than unity in the case of dissociation.