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Question:

Among the electrolytes Na2SO4, CaCl2, Al2(SO4)3 and NH4Cl, the most effective coagulating agent for Sb2S3 solution is:

NH4Cl

Na2SO4

CaCl2

Al2(SO4)3

Solution:

The correct option is C Al2(SO4)3
Sb2S3 is a negative sol. Al2(SO4)3 will be the most effective coagulant due to higher charge density on Al3+ by the Hardy-Schulze rule. According to the Hardy-Schulze rule, the greater the valency of the active ion, the greater will be its coagulating power.