NCERT MCQ Solutions for Class 12 Chemistry Chapter 1 Solutions

Solution of hydrogen in palladium as an example of a solid solution with a gaseous solute and a solid solvent.

Mass %, ppm, mole fraction, and molality are independent of temperature, whereas molarity depends on temperature because volume changes with temperature, but mass does not.

Henry’s law states that the partial pressure of the gas in vapour phase (p) is proportional to the mole fraction of the gas (x) in the solution, expressed as p = KH × x.

Raoult’s law for a solution of volatile liquids indicates the partial vapour pressure of each component (p1) is directly proportional to its mole fraction present in the solution (x1), given by p1 = p1° × x1.

Ideal solutions form when the intermolecular attractive forces (A-B) are nearly equal to those between pure components (A-A and B-B).
This results in ΔmixH = 0 and ΔmixV = 0.

In pure ethanol, molecules are hydrogen-bonded. Adding acetone breaks some of these bonds, weakening the intermolecular forces. This makes escaping easier, increasing vapour pressure and causing positive deviation.

Azeotropes as binary mixtures having the same composition in liquid and vapour phase and boiling at a constant temperature. It specifies they cannot be separated by fractional distillation.

Colligative properties depend on the number of solute particles, not their identity. The given lists relative lowering of vapour pressure, elevation of boiling point (ΔTb), depression of freezing point (ΔTf) and osmotic pressure (π) as examples. Boiling point itself is a property, while the elevation of boiling point is the colligative property.

The equation (p1° – p1)/p1° = x², stating that the relative lowering of vapour pressure ((p1° – p1)/p1°) is equal to the mole fraction of the solute (x²).

Kb (Boiling Point Elevation Constant or Ebullioscopic Constant) as a constant of proportionality in the equation ΔTb = Kb × m, and its value depends on the nature of the solvent.

Adding a non-volatile solute lowers the vapour pressure.
This leads to an elevation in the boiling point (ΔTb = Tb – Tb°) and a depression in the freezing point (ΔTf = Tf° – Tf).

Osmosis as the process of flow of the solvent through a semipermeable membrane (SPM) from pure solvent to the solution, or from a region of lower solute concentration to higher solute concentration.

Isotonic solutions as two solutions having the same osmotic pressure (π) at a given temperature. No net osmosis occurs between them when separated by an SPM.

Dissociation increases the total number of particles in the solution. Since i is the ratio of total moles of particles after dissociation/association to the number of moles of particles before dissociation/association, its value is greater than unity for dissociation.

Dimerisation means two molecules associate to form one particle (2 CH₃COOH ⇔ (CH₃COOH)₂).
This reduces the total number of particles.
If association is complete, the number of particles is halved.
The text mentions the value for ethanoic acid in benzene is nearly 0.5.

Reverse osmosis occurs when a pressure larger than the osmotic pressure (π) is applied to the solution side, forcing pure solvent out. It is used in the desalination of seawater.

A solution with > 0.9% NaCl is hypertonic relative to the cell fluid. Water will flow out of the cells via osmosis into the more concentrated surrounding solution, causing the cells to shrink.

The unit of Kf (Molal Depression Constant or Cryoscopic Constant) is K kg / mol (or K kg mol⁻¹).

The equation π = C × R × T for calculating the osmotic pressure (π) of dilute solutions, where C is molarity, R is the gas constant, and T is temperature.

The most commonly used form of Henry’s Law relates the partial pressure of the gas (p) to the mole fraction of the gas (x) in the solution: p = KH × x. Mole fraction is used as the measure of solubility in this form.