Question

Colloids can be purified by:
A. condensation
B. peptization
C. coagulation
D. dialysis

Answer 1

Hint: Think about the nature of colloidal solutions and what kind of particles are involved in its formation. Consider the processes happening during each of the methods given in the options and then determine the answer.

Complete step by step solution:
To answer this question, let us first look at what colloids are and then check each option and determine which one is the correct answer. An example of a colloid is milk, you can visualize whether the mentioned technique will be able to separate out the components of milk.
Colloids are a type of solid in liquid mixture where the size of the solid particles is so small that they cannot be separated out using our usual methods that are used to separate substances that are in different phases. This automatically rules out filtration and other such processes.
Now let us look at all the processes one by one and determine which one of them is the correct option.
- Condensation is a method that is usually used to separate out two liquids with a vast difference in boiling points or a solid that can be dissolved in the given liquid. Colloids do not fit into any of these criteria and thus, condensation is not the correct answer.
- Peptization is a process where any given precipitate in a solvent is turned into a colloidal solution. The particles of the precipitate are made finer so that it turns into a colloidal solution. This cannot be the correct answer since it is used to form colloids and not separate them.
- Coagulation is a method where any given liquid turns into a solid or a semi-solid. The suspended particles come together and the solvent or the aqueous part is taken away. This method cannot be used to separate colloids.
- Dialysis is a method where particles of a very small size that are suspended in a liquid are separated. Since colloids do have extremely small particles this method can be used to separate components of a colloid.

Hence, the correct answer to this question is ‘D. dialysis’

Note: Although coagulation may seem to be the correct answer, the particles in a colloid are far too small to form clumps and coagulate. Another method to separate colloids is centrifugation and works quite well with suspensions too.