Question

We sprinkle water in a dirty room before sweeping because:
A. water makes sweeping easier
B. water repels dust particles
C. water coagulates the dust particles
D. sprinkling water is fashionable

Answer 1

When we sprinkle the water, then the dust particles tend to get attracted towards the water in a similar way a bar magnet attracts iron filings. This helps in accumulation of dust particles which makes it easier to clean.

Complete answer:
The coagulation of a colloidal solution by an electrolyte does not take place until the added electrolyte has a certain minimum concentration in the solution. The concentration of the electrolyte in millimoles accounting to minimum that must be given to one litre of the sol so that complete coagulation takes place is called the coagulation value or flocculation value of the electrolyte for the sol.
Different electrolytes have different coagulation values. Smaller the coagulation value of the electrolyte larger is its coagulating or precipitating power. This can be expressed as follows.
The coagulation behavior of various electrolytes was studied in detail by Schulze and Hardy. They observed that:
(i) The ions carrying charge opposite to that of sol particles are effective in causing the coagulation of the sol. Such ions are called flocculating ions or active ions.
(ii) Coagulating power of an electrolyte is directly proportional to the fourth power of the valency of the active ions. This implies that greater the valency of the flocculating ion greater is its power to cause precipitation.
Water is sprinkled before sweeping the room as it helps to coagulate the dust particles. Light particles after coagulation become heavier and settle down due to which it becomes easier to remove them easily.

So the correct option will be (C).

Note:
The lyophilic sols are relatively more stable than lyophobic sols. The stability of lyophilic sols is due to two factors.
(i) Charge on the colloidal particles and
(ii) Solvation of colloidal particles because of greater attractive forces between dispersed phase and dispersion medium.