Question

Suspended impurities cannot be removed by:
A. Sedimentation
B. Addition of chemicals
C. Filtration
D. Electromagnetic method

Answer 1

Hint: Solve this question by taking a look at all the options and deciding which of these are efficient methods of removing a physical impurity.

Complete step by step answer:
Impurities in water are divided into dissolved and suspended solids. They are present in most surface waters.
Suspended impurities include suspended solids that are not completely soluble in water and are present as particles. These particles play a role in imparting a visible turbidity to the water. These impurities have a size ranging from 0.01 to 5 micrometer.
Suspended and dissolved impurities can be removed by sedimentation, filtration, coagulation, flocculation.
Now, let us look at the options given in the question.

Sedimentation – ‘Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration, or electromagnetism”.

Addition of chemicals – adding coagulants (chemicals such as - sodium poly alginate, polyacrylamide, etc.) leads to coagulation of suspended particles, which can easily be removed by physical methods.

Filtration – “Filtration is a process used to separate solids from liquids or gases using a filter medium that allows the fluid to pass through but not the solid”.

Electromagnetic method – It includes using electromagnetic forces. It is an inefficient manner of removing suspended particles as this needs to be separated by physical means.

As we can see, sedimentation, filtration and addition of chemicals are efficient methods of removing suspended impurities.

Therefore, the answer is – option (d) – Suspended impurities cannot be removed by electromagnetic method.

Note: Colloidal impurities are those which can be suspended in a substance just like their own make-up or a different substance with the exception of gases. Colloidal impurities are very small impurities, with a size less than 1000mm.