Chapter 2 : Is Matter around us pure?

• For a common person 'pure' means having no adulteration
• For a scientist, all these consumable items are actually mixtures of different substances and hence not pure
• Pure substance


  Consists of a single type of particles, all of which are the same in their chemical nature
• Most of the matter around us exist as mixtures of two or more pure components
• Mixture


  Constituted by more than one kind of pure form of matter, known as a substance
• A substance cannot be separated into other kinds of matter by any physical process
• Substances


  • Sodium chloride
  • Sugar
• Soft drink and soil are not single substances
• Whatever the source of a substance may be, it will always have the same characteristic properties
• Homogeneous mixture


  Mixture with uniform composition throughout
• Homogeneous mixtures


  • Salt in water
  • Sugar in water
• Heterogeneous mixture


  Mixture containing physically distinct parts and having non-uniform compositions
• Heterogeneous mixtures


  • Sodium chloride and iron filings
  • Salt and sulphur
  • Oil and water
• Solution


  A homogeneous mixture of two or more substances
• Solutions


  • Lemonade
  • Soda water
• Solvent


  The component of the solution that dissolves the other component (usually the component present in larger amount)
• Solute


  The component of the solution that is dissolved in the solvent (usually present in lesser quantity)
• Solutions


  • Sugar in water
  • Iodine in alcohol
  • Carbon dioxide in water
  • Oxygen and nitrogen in air
• Properties of a solution

  • Homogeneous mixture
  • Particle size smaller than 1 nm
  • Beam of light not scattered
  • Particles cannot be separated by filtration
  • Stable, particles do not settle
• Dilute solution

  Solution with relatively less solute
• Concentrated solution

  Solution with relatively more solute
• Saturated solution

  Solution that has dissolved as much solute as it is capable of dissolving at a given temperature
• Unsaturated solution


  Solution with less solute than the saturation level
• Solubility


  The amount of solute present in a saturated solution at a given temperature
• To express the concentration of a solution(The amount of solute present in a given amount of solution)

  • Concentration of solution = Amount of solute/ Amount of solution

  Or

  • Amount of solute/Amount of solvent
• To find the Concentration of the solution

  • (i) Mass by mass percentage of a solution =Mass of solute/Mass of solution×100
  • (ii) Mass by volume percentage of a solution =Mass of solute/Volume of solution×100
• Suspension


  A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium
• Suspension


  • Heterogeneous mixture
  • Solute particles visible to the naked eye
  • Particles scatter light and make path visible
  • Particles settle down when left undisturbed, can be separated by filtration
• Colloid


  Mixture where particles are uniformly spread throughout the solution, appear homogeneous but are actually heterogeneous
• Colloid


  • Heterogenous mixture
  • Particles too small to be seen by the naked eye
  • Particles scatter a beam of light (Tyndall effect)
  • Particles do not settle down, quite stable
  • Cannot be separated by filtration, require centrifugation
• Components of a colloid

  • Dispersed phase: The solute-like component or the dispersed particles in a colloid form the dispersed phase
  • Dispersion medium: The component in which the dispersed phase is suspended is known as the dispersing medium
  • Colloids are classified according to the state (solid, liquid or gas) of the dispersing medium and the dispersed phase
• Separating components of a mixture by evaporation

  1. Fill half a beaker with water and put a watch glass on the mouth of the beaker

  2. Put few drops of ink on the watch glass and heat mixture

  3. Volatile component evaporates

  4. Non-volatile component remains as residue
• Separating cream from milk by centrifugation

  1. Centrifuge full cream milk in a test tube for two minutes using a centrifuging machine or milk churner

  2. Denser cream settles at the bottom, and lighter milk stays at the top

  Applications:

  • Used in diagnostic laboratories for blood and urine tests.
  • Used in dairies and homes to separate butter from cream.
  • Used in washing machines to squeeze out water from wet clothes.
• Separating immiscible liquids by separating funnel


  1. Pour the mixture of immiscible liquids into a separating funnel

  2. Let layers separate based on density

  3. Open the stopcock and drain out the lower denser layer

  
  

  Applications

  • To separate the mixture of oil and water.
  • In extracting iron from its ore, the lighter slag is removed from the top to leave the molten iron at the bottom of the furnace.
• Separating mixture of salt and ammonium chloride by sublimation

  1. Heat mixture

  2. Ammonium chloride sublimates, salt remains
• Separating components of ink by chromatography

  1. Draw ink line on filter paper

  2. Dip in water just above the water level, water rises on the paper

  3. Components separate based on solubility

  Applications:

  • To separate colours in a dye
  • To separate pigments from natural colours
  • To separate drugs from blood
• Chromatography


  The process of separation of components of a mixture
• Kroma in Greek means colour. This technique was first used for separation of colours, so this name was given.
• Chromatography is the technique used for separation of those solutes that dissolve in the same solvent.
• The apparatus is similar to that for simple distillation, except that a fractionating column is fitted in between the distillation flask and the condenser.

  A simple fractionating column is a tube packed with glass beads. The beads provide a surface for the vapours to cool and condense repeatedly