Sublimation

Sublimation is a process in which solid is directly change into gas state without passing through liquid state. The substances which shows the process of sublimation are known as sublimate.
Examples of sublimate: Camphor, ammonium chloride, naphthalene etc.

Process: Sublimation is a technique used by chemists to purify compounds. A solid is typically placed in a

sublimation apparatus and heated under vacuum. Under this reduced pressure, the solid volatilizes and condenses as a purified compound on a cooled surface, leaving a non-volatile residue of impurities behind. Once heating ceases and the vacuum is removed, the purified compound may be collected from the cooling surface. 

Characteristics:

1. Sublimation is an endothermic process, i.e., heat is taken up from the surrounding for the phase transition.
2. Sublimation is a physical change and not a chemical change. For example, decomposition of ammonium chloride on heating to ammonia and hydrogen chloride is a chemical reaction and not sublimation. Also, combustion of hydrocarbons to carbon dioxide gas and water vapour is not sublimation.

Advantages:

1. Fast
2. Cheap

Disadvantages:

1. Non-sublimate compounds may decompose under heating.
2. Recovery may not be complete- the fumes may be blown away.

Sieving

Sieving is a separation technique in which unwanted particles are separated from the desired product on the basis of difference in the particle size of the two components of the mixture.
Common example is separating flour from unwanted material by passing it through a sieve. 

Sieve is the device which has small holes in it. Fine particles can easily pass through it, leaving behind coarse bigger particles.

A sieve can be operated by hands, as in our homes, and also can be used with the help of machines. In latter case, a large-sized sieve is connected to a machine which help in vibrating or moving the sieve. 

A strainer is a form of sieve used to separate a solid from a liquid. For example, separating tea leaves from tea.

Advantages:

1. It can be used to separate large amount of mixture when operated using a machine.
2. Easy handling
3. Saves time
4. Results are accurate and reproducible.

Disadvantages:

1. Consumes large amount of electrical energy, when operated using machine. Otherwise, it is a cheaper process.
2. It works only with dried mixture.