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Overview of Solutions

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Estimated time: 42 minutes
Maharashtra State Board: Class 12

Definition: Solution

A homogeneous mixture of two or more chemically non-reacting substances is called a solution.

Maharashtra State Board: Class 12

Definition: Solute

The component of a solution which is present in smaller quantity and gets dissolved is called solute.

Maharashtra State Board: Class 12

Definition: Solvent

The component of a solution which is present in larger quantity and dissolves the solute is called solvent.

Maharashtra State Board: Class 12

Definition: Solubility

The maximum amount of solute that can be dissolved in a given amount of solvent at a specific temperature is called solubility.

Maharashtra State Board: Class 12

Definition: Saturated solution

A solution that contains the maximum amount of solute at a given temperature is called a saturated solution.

Maharashtra State Board: Class 12

Definition: Unsaturated solution

A solution that contains less solute than the maximum amount that can be dissolved at a given temperature is called an unsaturated solution.

Maharashtra State Board: Class 12

Definition: Supersaturated solution

A solution that contains more solute than required for saturation at a given temperature is called a supersaturated solution.

Maharashtra State Board: Class 12

Definition: Osmotic pressure

The pressure required to stop the flow of solvent through a semipermeable membrane during osmosis is called osmotic pressure.

Maharashtra State Board: Class 12

Definition: Osmosis

The flow of solvent molecules through a semipermeable membrane from pure solvent or dilute solution to concentrated solution is called osmosis.

Maharashtra State Board: Class 12

Definition: Isotonic solutions

Two solutions having the same osmotic pressure at a given temperature are called isotonic solutions.

Maharashtra State Board: Class 12

Definition: Hypertonic solution

A solution having higher osmotic pressure than another solution is called a hypertonic solution.

Maharashtra State Board: Class 12

Definition: Hypotonic solution

A solution having lower osmotic pressure than another solution is called a hypotonic solution.

Maharashtra State Board: Class 12

Definition: Colligative properties

The physical properties of dilute solutions that depend only on the number of solute particles and not on their nature are called colligative properties.

Maharashtra State Board: Class 12

Definition: Reverse osmosis

The process in which solvent flows from solution into pure solvent through a semipermeable membrane by applying pressure greater than osmotic pressure is called reverse osmosis.

Maharashtra State Board: Class 12

Definition: Degree of dissociation

The fraction of total number of molecules that dissociate into ions is called degree of dissociation.

Maharashtra State Board: Class 12

Laws: Henry’s Law

Statement:
At constant temperature, the solubility of a gas in a liquid is directly proportional to the pressure of the gas above the solution.

Mathematical Expression:

S ∝ P

S = KHP

Where:
S = Solubility of gas
P = Pressure of gas
KH = Henry’s law constant

Maharashtra State Board: Class 12

Laws: Raoult’s Law

Statement:
At constant temperature, the partial vapour pressure of a volatile component in a solution is equal to the product of its mole fraction and vapour pressure in pure state.

Mathematical Expression:

P1 = P10 x1

For binary solution:

P = P1 + P2

Maharashtra State Board: Class 12

Laws: Dalton’s Law of Partial Pressures

Statement:
The total pressure exerted by a mixture of non-reacting gases is equal to the sum of the partial pressures of individual gases.

Mathematical Expression:

P = P1 + P2

Maharashtra State Board: Class 12

Laws: Law of Relative Lowering of Vapour Pressure

Statement:
For dilute solutions, the relative lowering of vapour pressure is equal to the mole fraction of the solute.

Mathematical Expression:

\[\frac{\Delta P}{P^0}=x_2\]

Maharashtra State Board: Class 12

Laws: Boiling Point Elevation Law

Statement:
The elevation in boiling point of a solvent is directly proportional to the molality of the solution.

Mathematical Expression:

ΔTb = Kbm

Where:
Kb = Ebullioscopic constant

Maharashtra State Board: Class 12

Laws: Freezing Point Depression Law

Statement:
The depression in freezing point of a solvent is directly proportional to the molality of the solution.

Mathematical Expression:

ΔTf = Kf m

Where:
Kf = Cryoscopic constant

Maharashtra State Board: Class 12

Laws: Osmotic Pressure Law (Van’t Hoff Law)

Statement:
The osmotic pressure of a dilute solution is directly proportional to its molar concentration at constant temperature.

Mathematical Expression:

π = MRT

Where:
π = Osmotic pressure
M = Molarity
R = Gas constant
T = Temperature in Kelvin

Maharashtra State Board: Class 12

Formula: van’t Hoff Factor

\[i=\frac{\text{Colligative property of electrolyte solution}}{\text{Colligative property of nonelectrolyte solution}}\]

\[i=\frac{\text{Actual moles of particles after dissociation}}{\text{Moles of formula units dissolved}}\]

Relation with degree of dissociation:

i = 1 + α(n − 1)

\[\alpha=\frac{i-1}{n-1}\]

Maharashtra State Board: Class 12

Key Points: Colligative properties of electrolytes

  • Solutions of electrolytes exhibit colligative properties, but they do not obey the same quantitative relations as nonelectrolyte solutions.
  • The observed colligative properties of electrolyte solutions are greater than those of nonelectrolyte solutions of the same concentration.
  • The molar masses of electrolytes determined from colligative property measurements are found to be lower than their expected formula masses.
  • The abnormal behaviour of electrolytes is due to their dissociation into two or more ions in aqueous solution, which increases the number of solute particles.
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