Question

Which of the following ionic substances will be more effective in precipitating the sulphur sol?
A.$\text{KCl}$
B.$\text{BaC}{{\text{l}}_{\text{2}}}$
C.$\text{F}{{\text{e}}_{\text{2}}}{{\left( \text{S}{{\text{O}}_{\text{4}}} \right)}_{3}}$
D.$\text{Na}{{\left( \text{P}{{\text{O}}_{\text{4}}} \right)}_{3}}$

Answer 1

Sulphur sols are colloidal solutions of elemental sulphur or sulphur-rich compounds. The particles in these solutions have diameters in the range of $\text{0}\text{.1-1}\text{.0 }\mu\text{ m}$ and consists of either ${{\text{S}}_{\text{8}}}$ molecules or chain-like sulphur compounds.

Complete answer:
The ${{\text{S}}_{\text{8}}}$ molecules are hydrophobic sulphur sols and chain like sulphur like sulphonate or functionalized organic groups are hydrophilic sulphur sols. Both these types of sols are stabilized by the negative charge of the particles that results in mutual repulsion. Therefore cations, specially the multivalent cations are able to precipitate the sol particles.
Hence, among the given salts, only barium chloride and ferrous sulphate solution have multivalent cations, among which the charge of the ferrous ions is higher, hence it should be more effective in precipitating the sulphur sol.

Thus, the correct option is C.
Note:
The hydrophilic sols are prepared with sulphur concentrations upto $\text{600 g }{{\text{L}}^{\text{-1}}}$, hydrophobic sols are much more dilute $\text{0}\text{.1 g }{{\text{L}}^{\text{-1}}}$. Sols of this type occur in both industrial desulphurization plants where sulphide is oxidized to elemental sulphur as well as in cultures of some oxidising sulphur bacteria. Sulphur sols are generally opalescent with a yellowish-white to yellow colour. When viewed by the transmitted light they appear to be bluish, but if freshly formed, may exhibit successively the colours yellow, green, red, violet, and blue. Such colour changes that depend on the degree of dispersion of the sulphur may conveniently be shown up by adding a dilute solution of phosphoric acid to $\dfrac{\text{N}}{\text{25}}$ sodium thiosulphate solution.