Question

Which of the following statements are correct?
(i) When an animal hide, which has negatively charged particles, is soaked in tannin, which contains positively charged colloidal particles, mutual coagulation does not take place.
(ii) Photographic films are prepared by coating an emulsion of the light sensitive silver bromide in gelatin over glass plates or celluloid films.
(iii) Latex is a colloidal solution of rubber particles which are negatively charged.
(iv) In Cottrell precipitator, the smoke, before it comes out from the chimney, is led through a chamber containing plates having a charge opposite to that carried by smoke particles. The particles on coming in contact with these plates acquire some charge and do not get precipitated.

• A. (i) and (iv) only
• B. (ii) and (iii) only
• C. (ii), (iii) and (iv) only
• D. All of these.

Answer 1

The correct option is B (ii) and (iii) only

There are various applications of colloids-

• Tanning: Animal hides are colloidal in nature. When a hide, which has positively charged particles, is soaked in tannin, which contains negatively charged colloidal particles, mutual coagulation takes place. This results in the hardening of leather. This process is termed as tanning. Chromium salts are also used in place of tannin.
  
• Photographic plates and films: Photographic plates or films are prepared by coating an emulsion of the light-sensitive silver bromide in gelatin over glass plates or celluloid films.
  
• Rubber industry: Latex is a colloidal solution of rubber particles which are negatively charged. Rubber is obtained by coagulation of latex.
  
• Electrical precipitation of smoke: Smoke is a colloidal solution of solid particles such as carbon, arsenic compounds, dust, etc., in air. The smoke, before it comes out from the chimney, is led through a chamber containing plates having a charge opposite to that carried by smoke particles. The particles on coming in contact with these plates lose their charge and get precipitated. The particles thus settle down on the floor of the chamber. The precipitator is called Cottrell precipitator.
  

Hence, option B shows the correct statements.