Elements Compounds and Mixtures Part-2

Tyndall Effect

When a beam of light is passed through a colloid the particles of the colloid scatter the beam of light and we can see the path of light in the solution. For Example, when a ray of light enters a dark room it is scattered by the dust particles present in the air and we can see the path of light clearly.

Components of a colloidal solution

Dispersed Phase – The dispersed particles or the solute-like components in a colloid 

Dispersing Medium – The substance in which these solute-like particles are added.

 

Separating the Components of a Mixture

1. Evaporation – For separating a mixture of a non-volatile and a volatile substance

  • Applications:
    • Separating coloured component from the ink
    • Salt from water
    • Sugar from Water
  • Method:
    • Mix some ink into water and heat it. After some time the water will evaporate leaving behind the coloured substance.

2. Centrifugation – Separating dense particles from lighter particles

  • Applications:
    • Separating milk from cream
    • Separating butter from cream
    • Squeezing out water from wet clothes
  • Method:
    • Milk is put in a centrifuging machine or milk churner and the cream thus separates from milk.

3. Using a Separating funnel – To separate two immiscible liquids

  • Applications:
    • Oil from water
    • Iron and iron ore
  • Method:
    • The immiscible liquids are allowed to settle in the funnel. They soon form separate layers due to varying densities. The first liquid is allowed to flow out of the funnel and as soon as it is completely poured out, the stopcock is closed thereby separating the two liquids from each other.  

4. Sublimation – To separate a sublimable component from a non-sublimable component

  • Applications:
    • Ammonium chloride / camphor / naphthalene and salt
  • Method:
    • Heat the mixture in an inverted funnel so that the sublimable component sublimes in the air and settles over the walls of the funnel and the non-sublimable component, on the other hand, is left behind.

5. Chromatography – To separate solutes that can dissolve in the same solvent 

 

  • Applications:
    • Separating colour components of a dye
    • Drugs from blood
  • Method:
    • Take a filter paper or a blotting paper and place a drop of ink at the rear end. Dip the end in water. Since ink is a mixture of two or more colors, the component of ink which is soluble in water mixes into it and then separates quickly from the other components that are less soluble in water.

6. Distillation – To separate miscible liquids (the boiling points of the liquids must be sufficiently different)

 

  • Applications:
    • Acetone and water
  • Method:
    • The mixture is heated in a distillation apparatus. The one substance with lower boiling point evaporates first, condenses and gets separated from the one with a higher boiling point.
    • Simple Distillation – when the miscible liquids have a satisfactory difference in their boiling points
    • Fractional Distillation – when the difference between the boiling points of the liquids is less than 25 K

 

Separating different Gases from the Air

 

Method – Fractional Distillation

  • Compress and cool the air by increasing the temperature and decreasing the pressure. The air turns to liquid air.
  • Liquid air is warmed up slowly in a fractional distillation apparatus
  • The several components of air get separated and are collected at various heights on the basis of their boiling points

 

Crystallization

In the crystallization method, we can obtain a pure solid in the form of crystals from its solution

  • Applications:
    • Salt from sea water
    • Purification of copper sulphate
  • Method:
    • The impurities of a substance are filtered out.
    • Water is evaporated to obtain a saturated solution.
    • The solution is covered with filter paper and left as it is.
    • After some time, the crystals of pure solid are formed.
  • Is evaporation better than crystallization?

    Simple evaporation is not better than crystallization because:

1. Some solid substances decompose because of excess heat. For Example, Sugar gets charred on extra heating.

2. If after filtration some impurities remain in the solution they can contaminate the solid and therefore we would not obtain a pure substance.