Question

II A (alkaline earth metals) and II B (zinc family) resemble:
A.$\text{MgS}{{\text{O}}_{\text{4}}}\text{.7}{{\text{H}}_{\text{2}}}\text{O}$ is isomorphous with $\text{ZnS}{{\text{O}}_{\text{4}}}\text{.7}{{\text{H}}_{\text{2}}}\text{O}$
B.II A and II B cations are not precipitated by ${{\text{H}}_{\text{2}}}\text{S}$ in acidic medium.
C.Both (a) and (b)
D.None of the above.

Answer 1

Hint:Two or more compounds are said to be isomorphous to each other when they are very similar structures. Both alkaline earth metals and zinc family has fully filled orbitals.

Complete step by step answer:
$\text{MgS}{{\text{O}}_{\text{4}}}\text{.7}{{\text{H}}_{\text{2}}}\text{O}$ is isomorphous with $\text{ZnS}{{\text{O}}_{\text{4}}}\text{.7}{{\text{H}}_{\text{2}}}\text{O}$ - The common name for Zinc Sulphate heptahydrate is “White Vitriol”. Both Magnesium Sulphate heptahydrate and White Vitriol have the same number of component ions and the charges on the cations are also equal. These are the major requirements for two compounds to be isomorphous. Hence they are isomorphous to each other.
II A and II B cations are not precipitated by ${{\text{H}}_{\text{2}}}\text{S}$ in acidic medium –After the group I cations are precipitated cation solution is treated with${{\text{H}}_{\text{2}}}\text{S}$, when insoluble precipitate of mercuric sulphide and cadmium sulphide is formed. Hence it can be said that group II A cations are not precipitated by hydrogen sulphide in the acidic medium but two cations from group II B are precipitated.

Hence, the correct answer is option A.

Note:
In the qualitative analysis of the cations, mercury and cadmium fall in group II, while zinc falls in group III, calcium, barium, and strontium in group IV, and magnesium in group V. In the qualitative analysis of the cations, the group I cations are initially precipitated used dilute hydrochloric acid. Group III cations are precipitated by hydrogen sulphide in the basic medium, group IV cations are precipitated by ammoniacal ammonium chloride, lastly group V cations remain.