Question

Solid-solid mixtures are separated by:

• A. Filtration
• B. Distillation
• C. Sublimation
• D. None of these

Answer 1

Answer: (A), (C)

The correct options are
A Filtration
C Sublimation

Physical separation techniques depend on the physical properties of the substance. These physical properties include physical state, solubility, boiling point, melting point, density, specific gravity, electrical and magnetic properties.

1. Washing: Insoluble solids like noble metals and compounds like silica can be washed with water until all the other impurities leave them. Washing can also be done with organic solvents when there is a mixture with soluble impurities and insoluble compound.
2. Decanting: When the densities of two liquids that are immiscible in one another are to be separated this method can be used. Separating funnel helps to separately collect the tow liquids. In case of solids the lighter solids can be separated by decanting it in water medium when both of the solids are not soluble. By blowing air also the separation can be done with very light and heavy solid mixtures.
3. Distillation: Mixtures of liquids can be separated when their boiling points are different by this technique. The mixture is slowly heated in a distillation flask. The component having the low boiling point vaporizes first. The vapors are collected by condensing them in Leibig's condenser. Mixtures containing more than two liquids can also be separated by this technique but the difference in boiling points must be at least 20C between each of them. Distillation can also be used to separate dissolved salts from their aqueous solutions. Sea water is distilled by the Sun rays to form clouds which rain fresh water without salts. Mixture of gases are separated by reducing their temperature and converting all the gases in to liquid state. By gradational increasing of temperatures each liquified gas gets converted into gaseous state and can be separated.
4. Fractional distillation: When the difference in the boiling points are nearby to each other and not much, a detailed distillation is carried out which is called fractional distillation. It is done in a column called fractionating column. Fractionating column allows the condensation of different solvents at different temperatures and sending back the mixture fraction in to the flask. Petroleum distillation is done in the fractionating column in to various components over a wide range of temperatures. Melting point differences can also be utilized in the same way as boiling point in separation of mixtures. Icebergs are formed which are solidified fresh water is based on the depression of freezing point phenomenon.
5. Solubility: Different compounds have different amounts of solubility at a certain temperature. When no more solid is soluble in solvent at a particular temperature it is called its saturation point at that temperature. In a mixture if one component is more soluble and the other less at a given temperature, they can be separated by this technique.
6. Electrical and Magnetic separation: Electrolytes and non electrolytes, magnetic and non magnetic substances can be separated by this technique of separation using either electrical field or magnetic field.