Question

Butter from curd can be separated by:
(A)- dissolution
(B)- sublimation
(C)- centrifugation
(D)- crystallization

Answer 1

Hint: Curd is a colloid in which the dispersed phase is liquid (i.e. water) and dispersion medium is solid (i.e. fat). This type of colloidal solution is called gel. Centrifugation is the method of separation of substances from a solution, colloid or suspension based on their density, size, shape, speed of the rotor and viscosity of the medium.

Complete step by step answer:
Butter from curd is separated by the technique of centrifugation.
The instrument used for the process of centrifugation consists of a rotor and is called centrifuge.
In this centrifuge, when curd is spun rapidly and constantly, denser particles are forced to the bottom whereas lighter particles move away from the centrifuge and remain on the top.
Centrifugation method involves the centrifugal force to separate lighter particles from the denser particles. On rapid rotation, a centrifugal force develops in the particles, which pushes the dense particles (milk fat) to settle at the bottom while butter stays at the top as it has a lesser density than the skimmed curd liquid.
Let us see why the other methods are not suitable for separation of butter from curd.
Dissolution is the process of dissolving a gaseous, liquid or solid solute in a solvent to form a solution hence, butter cannot be separated by this process.
We also cannot use sublimation since it involves the conversion of converting solid into gaseous state.
Crystallization is a method used for purification of compounds, generally solids. So it also cannot be used. So, the correct answer is “Option C”.

Note: Do not confuse dissolution with centrifugation. Dissolution is simply dissolving a solute in solvent to form a solution. Sublimation and crystallization methods are applicable on solid states of a substance.