Question

Which of the following processes is used to separate cream from milk?
A. Filtration
B. Distillation
C. Chromatography
D. Centrifugal Separation

Answer 1

Hint: Think about the particle size, viscosity, density, and other physical properties of both cream and milk. Take note of how they differ and then determine using which method they can be separated on the basis of these properties.

Complete step by step answer:
Let us look at each of these processes individually and then determine which of these processes would help with the separation of cream from milk.

A) Filtration is a physical, biological or chemical operation that is used for the separation of solids and fluids from a mixture of the two with a medium used as a filter that possesses a complicated structure which allows only the liquid to pass, with the solid particles that cannot pass through the filter medium are being oversized and the fluid that passes through simply being referred to as the filtrate.
B) Distillation on the other hand is the process of separating the components or substances from a liquid mixture by the usage of selective boiling and condensation for the same. While it is possible that distillations result in the complete separation of the components in question, it is also likely that there may be a partial separation that takes place.
C) A completely different procedure from the two elaborated upon above is chromatography, which is a laboratory technique used for the separation of a mixture and finds its roots in surface chemistry. In chromatography, the mixture is dissolved in a fluid called the mobile phase to begin with, which then carries it through another material called the stationary phase. Due to the various speeds of the constituents of the mixture, they end up separating.
D) The most suitable technique of separation of milk and cream however, is the use of a centrifugal separator. This machine can be likened to a drum which is driven round by a belt and pulley. The cream, which is lighter than the milk, is driven by centrifugal force to the surface of the milk and flows off into a channel from which it is led into a collection vessel. Under it, the milk is forced out to the periphery of the drum and is collected in another channel, whence it is led to a separate collecting vessel.

Thus, we can easily conclude that the answer to this question is ‘D. Centrifugal separation’.

Note: Before the advent of centrifugal separators, separation was performed by letting milk sit in a container until the cream floated to the top and could be skimmed off by hand. This is used in Indian households to this day for the production of homemade cream i.e. malai.