Question
Under the influence of an electric field, the particles in a sol migrate towards cathode. The coagulation of the same sol is studied using $$NaCl,N{a_2}S{O_4}$$ and $$N{a_3}P{O_4}$$ solutions. Their coagulating values will be in the order
A.
$$NaCl > N{a_2}S{O_4} > N{a_3}P{O_4}$$
B.
$$N{a_2}S{O_4} > N{a_3}P{O_4} > NaCl$$
C.
$$N{a_3}P{O_4} > N{a_2}S{O_4} > NaCl$$
D.
$$N{a_2}S{O_4} > NaCl > N{a_3}P{O_4}$$
Answer :
$$NaCl > N{a_2}S{O_4} > N{a_3}P{O_4}$$
Solution :
Since the sol particles migrate towards cathode, they are positively charged. Hence,
anions would be effective in coagulation. Greater is the valency of effective $$ion,$$ smaller will be its coagulating value.