Question

Find the number of yellow coloured water-insoluble compounds.
$\text{ Pb}{{\text{I}}_{\text{2}}}\text{ }$, $\,\text{PbCr}{{\text{O}}_{\text{4}}}\text{ }$, $\text{ KI }$ , $\text{ NaI }$,$\text{ A}{{\text{g}}_{\text{2}}}\text{Cr}{{\text{O}}_{\text{4}}}\text{ }$,$\,\text{BaCr}{{\text{O}}_{\text{4}}}\text{ }$,$\text{ }{{\text{K}}_{\text{2}}}\text{Cr}{{\text{O}}_{\text{4}}}\text{ }$,$\text{ }{{\left( \text{N}{{\text{H}}_{\text{4}}} \right)}_{\text{3}}}\text{P}{{\text{O}}_{\text{4}}}\text{.10Mo}{{\text{O}}_{\text{3}}}\text{ }$,$\text{ HgO }$ , $\text{ AgI }$, $\text{ AgCl }$

Answer 1

Hint: When an ionic compound dissolves in the water, it dissociates into its component ions. This dissociation of the compound either gives or takes the energy from the surrounding. Larger size ions reduce the solubility of the compound. Iodide, chromate, sulphate, barium ion, etc. are bigger size ions and do not readily get dissolved in water.

Complete answer:
When an ionic compound dissolves in the water, it dissociates into its component ions. This dissociation of the compound either gives or takes the energy from the surrounding.
1) $\text{ Pb}{{\text{I}}_{\text{2}}}\text{ }$ : Lead iodide is a yellow coloured compound.it is insoluble in water at room temperature. Lead iodide dissociated into its component lead ion $\text{ P}{{\text{b}}^{\text{2+}}}\text{ }$and iodide ion $\text{ }{{\text{I}}^{-\text{ }}}$ . The dissociation of lead iodide takes out the energy from the surrounding and increases the temperature of the solution. The dissociation of lead iodide is taken place only in high temperatures.at room temperature lead iodide is insoluble in water.
2) $\,\text{PbCr}{{\text{O}}_{\text{4}}}\text{ }$ : The lead chromate is a yellow colour inorganic compound. Many of the lead salt is insoluble in water. In Hard soft acid-base (HSAB) theory lead is a borderline acid and thus acts as hard and soft. However, water is a hard solvent. According to HSAB theory, hard-hard or soft-soft interaction is allowed. Thus lead ion does not interact with water. Thus lead chromate is insoluble in water.
3)$\,\text{BaCr}{{\text{O}}_{\text{4}}}\text{ }$: The barium chromate is an inorganic compound. It is a fine yellow coloured powder. The barium chromate is insoluble in water. Chromium compounds are insoluble in water. These are because they are bigger and they are bound to the surface water molecules. Barium ion is also a bigger molecule which reduces the solubility of barium chromate. The barium chromate is soluble in an acidic medium.
4) $\text{ }{{\left( \text{N}{{\text{H}}_{\text{4}}} \right)}_{\text{3}}}\text{P}{{\text{O}}_{\text{4}}}\text{.10Mo}{{\text{O}}_{\text{3}}}\text{ }$: Ammonium phosphomolybdate is an inorganic salt. It is a phosphomolybdate ion complex. It is a yellow coloured compound.it is insoluble in water.it is soluble in alkali, ammonia, and phosphoric acid.
5) $\text{ HgO }$ : Mercuric oxide is an inorganic compound. Mercuric oxide is a yellow coloured compound.it is insoluble in water.
6) $\text{ AgI }$ : Silver iodide is less soluble in the water because silver iodide has a more covalent character and the two atoms have similar atomic radii. Thus they form a strong bond in their lattice structure. Thus the solubility product of silver iodide is small. It is a yellow coloured compound.
Silver chromate $\text{ A}{{\text{g}}_{\text{2}}}\text{Cr}{{\text{O}}_{\text{4}}}\text{ }$ is a brick red coloured compound .potassium chromate $\text{ }{{\text{K}}_{\text{2}}}\text{Cr}{{\text{O}}_{\text{4}}}\text{ }$is soluble in water and forms a yellow coloured solution. Silver chloride $\text{ AgCl }$ forms a white precipitate in solution. Potassium iodide and sodium iodide are water-soluble compounds.
Thus there are a total of 6 inorganic compounds that are yellow in colour and insoluble in water.

Hence, (A) is the correct option.

Note: Note that the compound is insoluble in water when the bonding between the species is not stronger. Those inorganic compounds which have weaker attraction between the ions readily dissociate into the solution. Various theories like HSAB theory, atomic radii, polarizability, and temperature affect the solubility of compounds.