Question

Cloud is an example of foam. This statement is:
(A) True
(B) False

Answer 1

Hint: Cloud is a prime example of a colloid. There are a number of colloids possible. By identifying which particles are suspended in which medium in the cloud, it will be possible to determine which colloid a cloud is.

Complete answer:
In order to justify the above statement, let us first know about colloids.
What is colloid?
When one substance of microscopically dispersed particles is suspended in another substance and thus, creates a phase separated mixture, then it is called a colloid.
The main difference between a colloid and a normal solution is that the solute and solvent of a solution creates only one phase, whereas, a colloid has two phases, known as a dispersed phase and a continuous phase. The dispersed phase consists of the suspended particles and the continuous phase is the medium of suspension.
Now, there is a number of different colloids available:
Aerosol: In this colloid, liquid or solid particles are suspended in a gas. When liquid particles are suspended in the gas, then it is termed as liquid aerosol and when solid particles are suspended in the gas, then it is known as solid aerosol.
Example: fog, cloud, smoke etc.
Emulsion: When liquid particles are suspended in liquid, then the colloid is known as emulsion.
Example: milk, mayonnaise etc.
Foam: When gas particles are suspended in liquid, then the colloid is known as foam.
Example: whipped cream, shaving cream etc.
Sol: When solid particles are suspended in liquid, then the colloid is called sol.
Example: precipitates
Gel: When liquid particles are suspended in the solid, then it is known as gel.
Example: jelly, gelatine etc.
Now, clouds are a prime example of colloids.
A cloud generally consists of liquid droplets or frozen solid crystals that are suspended in the atmosphere.
Hence, a cloud is basically liquid or solid particles suspended in the gas. Then, according to the definition of colloids, it should be an aerosol colloid.
Whereas, a foam, which has already been mentioned, is nothing but gas particles suspended in liquid. One of prime examples of foam is whipped cream.
Thus, clouds cannot be foam, but they are aerosols.
Hence, we have arrived at the conclusion that clouds are not an example of foam.
Hence, option B is the correct answer to this question.

Note: While identifying the colloid, students have to determine properly which substance is suspended in which medium. This is because, as the medium and the substance change, the nature of the colloid is also changed.
For example: When the liquid particles are suspended in a gas medium, the nature of the colloid is liquid aerosol. On the other hand, when gas particles are suspended in liquid medium, the nature of the colloid is foam.
Hence, the correct identification of the dispersed phase and the dispersed medium is very important in order to correctly determine the colloid.