CLASS 12 CHEMISTRY
CHAPTER 1 — SOLUTIONS
Detailed NCERT-based notes • Board + NEET revision • Concepts + formulas + numericals
Chapter Overview
A solution is a homogeneous mixture of two or more components. This chapter mainly deals with concentration terms,
solubility, vapour pressure, Raoult’s law, ideal/non-ideal solutions, colligative properties, osmotic pressure, and abnormal
molar masses.
Most important for numericals: molarity, molality, mole fraction, Henry’s law, Raoult’s law, relative lowering of vapour
pressure, elevation of boiling point, depression of freezing point, osmotic pressure and van’t Hoff factor.
1. What is a Solution?
A solution is a homogeneous mixture of two or more chemically non-reacting components. The composition is uniform
throughout the mixture.
The component present in larger amount is called the solvent, while the component present in smaller amount is called
the solute. The physical state of a solution is generally determined by the solvent.
Examples:
• Salt + water → salt is solute, water is solvent.
• Sugar + water → sugar is solute, water is solvent.
• Air → mixture of gases; nitrogen is the major component.
• Brass → solid solution of copper and zinc.
2. Types of Solutions
Solute Solvent Example
Gas Gas Air
Gas Liquid CO■ in water
Gas Solid H■ in palladium
Liquid Gas Water vapour in air
Liquid Liquid Ethanol in water
Liquid Solid Amalgam (liquid Hg in solid metal)
Solid Gas Smoke / solid particles in air
Solid Liquid Salt in water
Solid Solid Brass
3. Concentration of a Solution
Concentration tells us how much solute is present in a specified amount of solution or solvent. Different concentration
units are useful for different calculations.
3.1 Mass Percentage
Mass % = (Mass of solute / Mass of solution) × 100
Mass of solution = mass of solute + mass of solvent.
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, Example: If 10 g NaCl is present in 90 g water, mass of solution = 100 g and mass % = 10%.
3.2 Volume Percentage
Volume % = (Volume of solute / Volume of solution) × 100
This is commonly used for liquid-liquid solutions such as alcohol in water.
3.3 Mass by Volume Percentage
Mass/Volume % = (Mass of solute in g / Volume of solution in mL) × 100
3.4 Parts per Million (ppm)
ppm = (Number of parts of component / Total number of parts of solution) × 10■
ppm is useful for very dilute solutions, such as trace pollutants in air or water.
3.5 Mole Fraction
For component i: χ■ = n■ / (n■ + n■ + n■ + …)
For a binary solution: χ■ + χ■ = 1.
3.6 Molarity
Molarity is the number of moles of solute dissolved per litre of solution.
M = moles of solute / volume of solution in litres
Important: Molarity is temperature dependent because volume changes with temperature.
3.7 Molality
Molality is the number of moles of solute present in 1 kg of solvent.
m = moles of solute / mass of solvent in kg
Important: Molality is independent of temperature because mass does not change appreciably with temperature.
4. Relation Between Molarity and Molality
A useful relation for converting concentration terms is:
m = 1000M / (1000d − M M■)
where d = density of solution in g mL■¹ and M■ = molar mass of solute in g mol■¹.
5. Solubility
Solubility is the maximum amount of a substance that can dissolve in a specified amount of solvent at a particular
temperature and pressure to form a saturated solution.
Saturated solution: contains the maximum amount of solute that can dissolve under the given conditions.
Unsaturated solution: contains less solute than the maximum possible amount.
Supersaturated solution: contains more dissolved solute than normally possible under equilibrium conditions and is
unstable.
6. Solubility of a Solid in a Liquid
The solubility of most solids in liquids increases with temperature, but the actual effect depends on the enthalpy change
of dissolution. Pressure generally has little effect on the solubility of solids in liquids.
If dissolution is endothermic, increasing temperature generally increases solubility. If dissolution is exothermic,
increasing temperature may decrease solubility.
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CHAPTER 1 — SOLUTIONS
Detailed NCERT-based notes • Board + NEET revision • Concepts + formulas + numericals
Chapter Overview
A solution is a homogeneous mixture of two or more components. This chapter mainly deals with concentration terms,
solubility, vapour pressure, Raoult’s law, ideal/non-ideal solutions, colligative properties, osmotic pressure, and abnormal
molar masses.
Most important for numericals: molarity, molality, mole fraction, Henry’s law, Raoult’s law, relative lowering of vapour
pressure, elevation of boiling point, depression of freezing point, osmotic pressure and van’t Hoff factor.
1. What is a Solution?
A solution is a homogeneous mixture of two or more chemically non-reacting components. The composition is uniform
throughout the mixture.
The component present in larger amount is called the solvent, while the component present in smaller amount is called
the solute. The physical state of a solution is generally determined by the solvent.
Examples:
• Salt + water → salt is solute, water is solvent.
• Sugar + water → sugar is solute, water is solvent.
• Air → mixture of gases; nitrogen is the major component.
• Brass → solid solution of copper and zinc.
2. Types of Solutions
Solute Solvent Example
Gas Gas Air
Gas Liquid CO■ in water
Gas Solid H■ in palladium
Liquid Gas Water vapour in air
Liquid Liquid Ethanol in water
Liquid Solid Amalgam (liquid Hg in solid metal)
Solid Gas Smoke / solid particles in air
Solid Liquid Salt in water
Solid Solid Brass
3. Concentration of a Solution
Concentration tells us how much solute is present in a specified amount of solution or solvent. Different concentration
units are useful for different calculations.
3.1 Mass Percentage
Mass % = (Mass of solute / Mass of solution) × 100
Mass of solution = mass of solute + mass of solvent.
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, Example: If 10 g NaCl is present in 90 g water, mass of solution = 100 g and mass % = 10%.
3.2 Volume Percentage
Volume % = (Volume of solute / Volume of solution) × 100
This is commonly used for liquid-liquid solutions such as alcohol in water.
3.3 Mass by Volume Percentage
Mass/Volume % = (Mass of solute in g / Volume of solution in mL) × 100
3.4 Parts per Million (ppm)
ppm = (Number of parts of component / Total number of parts of solution) × 10■
ppm is useful for very dilute solutions, such as trace pollutants in air or water.
3.5 Mole Fraction
For component i: χ■ = n■ / (n■ + n■ + n■ + …)
For a binary solution: χ■ + χ■ = 1.
3.6 Molarity
Molarity is the number of moles of solute dissolved per litre of solution.
M = moles of solute / volume of solution in litres
Important: Molarity is temperature dependent because volume changes with temperature.
3.7 Molality
Molality is the number of moles of solute present in 1 kg of solvent.
m = moles of solute / mass of solvent in kg
Important: Molality is independent of temperature because mass does not change appreciably with temperature.
4. Relation Between Molarity and Molality
A useful relation for converting concentration terms is:
m = 1000M / (1000d − M M■)
where d = density of solution in g mL■¹ and M■ = molar mass of solute in g mol■¹.
5. Solubility
Solubility is the maximum amount of a substance that can dissolve in a specified amount of solvent at a particular
temperature and pressure to form a saturated solution.
Saturated solution: contains the maximum amount of solute that can dissolve under the given conditions.
Unsaturated solution: contains less solute than the maximum possible amount.
Supersaturated solution: contains more dissolved solute than normally possible under equilibrium conditions and is
unstable.
6. Solubility of a Solid in a Liquid
The solubility of most solids in liquids increases with temperature, but the actual effect depends on the enthalpy change
of dissolution. Pressure generally has little effect on the solubility of solids in liquids.
If dissolution is endothermic, increasing temperature generally increases solubility. If dissolution is exothermic,
increasing temperature may decrease solubility.
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