Question

The clouds consists of charged particles of water dispersed in air. Some of them are positively charged, others are negatively charged. When positively charged clouds come closer, they cause lightening and thundering whereas when positive and negative charged colloids come closer, they cause heavy rain by aggregation of minute particles. It is possible to cause artificial rain by throwing electrified sand or silver iodide from an aeroplane and thus, coagulation the mist hanging in air.

AgI helps in artificial rain because :

• A. it helps in coagulation
• B. it helps in dispersion process
• C. both A and B
• D. none of the above

Answer 1

The correct option is C both A and B

Coagulation/Flocculation :

The presence of small amounts of appropriate electrolytes is necessary for the stability of the colloids.

However, when an electrolyte is added in larger concentration; the particles of the sol take up the ions which are oppositely charged and thus get neutralised. The neutral particles then start aggregating giving particles of larger size which are then precipitated. This process of aggregation of colloidal particles into an insoluble precipitate by the addition of some suitable electrolyte is known as coagulation.

Solid silver iodide is preferred as a nucleator for artificially stimulated rain because its crystal lattice parameters are close to those of ice, and for that reason are more effective than other salts in causing small ice crystals in clouds to melt.