Solutions: Characteristics of a Solution, Henry՚s Law, Raoult՚s Law (For CBSE, ICSE, IAS, NET, NRA 2022)

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A Solution Solvent and Solute
  • A solution comprises a solute and a solvent.
  • A solution is a homogeneous mixture of two or more substances. A solution may exist in any phase
  • It is defined as a homogeneous mixture of two or more than two substances.
  • A solution consists of a solute and a solvent. The solute is the substance that is dissolved in the solvent.
  • The amount of solute that can be dissolved in solvent is called its solubility
  • They can be classified into three types:
    • Solid solutions
    • Gaseous solutions
    • Liquid solutions
  • For solutions with components in the same phase, the substances present in lower concentration are solutes, while the substance present in highest abundance is the solvent.
  • Molarity, mole fraction, percentages, and molality are the terms used to express the concentration of a solution.
  • Using air as an example, oxygen and carbon dioxide gases are solutes, while nitrogen gas is the solvent.

Characteristics of a Solution

  • A solution consists of a homogeneous mixture.
  • A solution is composed of one phase (e. g. , solid, liquid, gas) .
  • Particles in a solution are not visible to the naked eye.
  • A solution does not scatter a light beam.
  • Components of a solution cannot be separated using simple mechanical filtration.

Henry՚s Law

The Henry՚s Law
  • In liquids, the dissociation of gas is controlled by Henry՚s law.
  • In physical chemistry, Henry՚s law is a gas law that states that the amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid.
  • The states that, the solubility of a gas in a liquid, at a given temperature, is directly proportional to the partial pressure of the gas.
  • The proportionality factor is called Henry՚s law constant
  • Due to the presence of a non-volatile solute, the vapour pressure of the solvent is lowered.

Raoult՚s Law

The Raoult՚s Law
  • The lowering of the vapor pressure of the solvent is ruled by Raoult՚s law.
  • Raoult՚s law is a law of physical chemistry, with implications in thermodynamics.
  • The law states that the relative lowering of the vapor pressure of the solvent over a solution and the mole fraction of a non-volatile solute present in the solution is equal.

Ideal Solutions

  • An ideal solution is a mixture in which the molecules of different species are distinguishable, however, unlike the ideal gas, the molecules in ideal solution exert forces on one another.
  • When a solution obeys Raoult՚s law over the entire range of concentrations it is called an ideal solution.
  • When those forces are the same for all molecules independent of species then a solution is said to be ideal.

Types of deviations from Raoult՚s law:

  • Positive deviations
  • Negative deviations

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