Molality is defined as the number of moles of the solute particles which dissolved in unit weight of the solvent. It can be represented by the symbol m . m = Number of moles of solute Mass of the solvent ( in kg ) m = n B W A ( kg ) ∵ n B = W B M B m = W B M B × 1000 W A Where W B and W A are the mass of solute and solvent, respectively.

What is freezing point of a liquid? The freezing point of pure benzene is 278.4 K. Calculate the freezing point of the solution when 2.0 g of a solute having molecular weight 100 g mol - 1 is added to 100 g of benzene. (Kf of benzene = 5 . 12 K kg mol - 1 .)

The Freezing point is the temperature of a liquid at which it changes its state from liquid to solid at atmospheric pressure. We know, ∆ T f = 1000 K f W 2 M 2 W 1 ∆ T f = 1000 × 5 . 12 × 4 100 × 200 = 1 . 024 K T f = T f ∘ - ∆ T f = 278 . 4 - 1 . 024 = 277 . 376 K

Derive van’t Hoff general solution equation for ‘n’ moles of solute.

Consider a dilute solution of a volume V (in dm3) containing W grams of a substance having molecular weight M at an absolute temperature T. Then, concentration of the solution, C=n/V and No. of moles of the substance, n=W/M. By Boyle's law, at a constant temperature, the osmotic pressure of a solution is directly proportional to its molar concentration or inversely proportional to the volume of the solution. Thus, π α C (when temperature is constant) Charle's law at the constant concentration the osmotic pressure of a dilute solution is directly proportional to the absolute temperature(T) i.e. π α C π α CT v = CRT . The equation is called Van't Hoff general solution equation. R is constant of proportionality, also called general solution constant or gas constant.

Derive van’t Hoff general solution equation.

According to van't Hoff Boyle's law, The osmotic pressure π of a dilute solution is directly proportional to the concentration at a constant temperature. π ∝ C ⋯ ⋯ ⋯ ⋯ ( i ) According to van't Hoff Charles law, The osmotic pressure π of a dilute solution is directly proportional to the absolute temperature at a constant concentration C . π ∝ T ⋯ ⋯ ⋯ ⋯ ( ii ) From equation i and ii , π ∝ CT π = CRT ⋯ ⋯ ⋯ ⋯ ( iii ) The above equation is called van't Hoff general solution equation.

Define the following term: Hypotonic solution

The solution which has less osmotic pressure than the other solution is called hypotonic. It means that the concentration of this type of solution is less with respect to other solutions. For example, 0 . 05 M sucrose solution exerts lower osmotic pressure than 0 . 01 M urea solution. Therefore, 0 . 05 M sucrose solution is hypotonic to 0 . 0 M urea solution.

Define the following term: Hypertonic solution

The solution that is more concentrated with respect to the other solution is called hypertonic solution. It means that the hypertonic solution has more osmotic pressure with respect to other solutions. For example, 0 . 01 M urea solution exerts higher osmotic pressure than 0 . 05 M sucrose solution. Hence, 0 . 01 M urea solution is hypertonic to 0 . 05 M sucrose solution.

Define the following term: Isotonic solution

The solution which has the same osmotic pressure with respect to other solution at the same temperature is called isotonic solution or isosmotic solution. π = C × R × T From this equation, it can be said that the osmotic pressures of solution that has the same concentration is same.

E M B I B E

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY>Chapter 2 - Solutions and Colligative Properties>Maharashtra Board-2020>Q 10

EASY

12th Maharashtra Board

IMPORTANT

Earn 100

Define: Molality

Important Questions on Solutions and Colligative Properties

EASY

12th Maharashtra Board

IMPORTANT

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY>Chapter 2 - Solutions and Colligative Properties>Maharashtra Board-2020>Q 11

Define: Osmotic pressure

HARD

12th Maharashtra Board

IMPORTANT

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY>Chapter 2 - Solutions and Colligative Properties>Maharashtra Board-2020>Q 12

Derive the mathematical expression between molar mass of a non-volatile solute and elevation of boiling point.
State and explain van’t Hoff-Avogardo’s law.

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