Question

Which of the following is isomorphous with ${\text{MgS}}{{\text{O}}_{\text{4}}}{\text{.7}}{{\text{H}}_{\text{2}}}{\text{O}}$ ?
(A) Green vitriol
(B) Blue vitriol
(C) Red vitriol
(D) Vitriol of Mars

Answer 1

- Two substances are said to be isomorphous if they have the same chemical formulation.
- Isomorphous crystals must possess atoms having corresponding chemical properties. The size of the corresponding atoms should also be similar.

Complete step by step answer:
Epsom salt is actually magnesium sulfate in the most common form which is magnesium sulfate heptahydrate or ${\text{MgS}}{{\text{O}}_{\text{4}}}{\text{.7}}{{\text{H}}_{\text{2}}}{\text{O}}$ . It loses one equivalent of water to form the hexahydrate which has octahedral geometry.

Green vitriol is another name of crystalline ferrous sulphate or iron (II) sulphate. The most commonly encountered form is the heptahydrate form. It has the chemical formula ${\text{FeS}}{{\text{O}}_{\text{4}}}{\text{.7}}{{\text{H}}_{\text{2}}}{\text{O}}$ . It is bluish – green in colour. It dissolves in water to give the hexahydrated form which has octahedral geometry.

Thus, green vitriol has the same chemical formulation as magnesium sulphate heptahydrate or Epsom salt. They also have similar shape and chemical properties. So, they are isomorphous and hence, option A is correct.
Blue vitriol is just another name for copper sulphate or copper (II) sulphate. The most commonly encountered form of copper sulphate is copper sulphate pentahydrate which is bright blue in colour. It has the chemical formula ${\text{CuS}}{{\text{O}}_{\text{4}}}{\text{.5}}{{\text{H}}_{\text{2}}}{\text{O}}$ . Thus, it has a different chemical formulation than that of magnesium sulphate heptahydrate and so they are not isomorphous. So, option B is wrong.
Red vitriol is cobalt (II) sulphate heptahydrate having the chemical formula ${\text{CoS}}{{\text{O}}_{\text{4}}}{\text{.7}}{{\text{H}}_{\text{2}}}{\text{O}}$. The size of the cobalt atom is not similar to that of magnesium in Epsom salt and hence C is also wrong.
Vitriol of Mars is ferric sulphate or iron (III) sulphate having the chemical formula ${\text{F}}{{\text{e}}_2}{\left( {{\text{S}}{{\text{O}}_{\text{4}}}} \right)_3}$ . Thus, it has a different chemical formulation than that of magnesium sulphate heptahydrate and so they are not isomorphous. So, option D is wrong.

Note:
- The main external use of Epsom salt is the formulation of bath salts to treat sore feet. It is also used as a saline laxative.
- Epsom salt also leads to the release of cholecystokinin and this in turn causes the increase of intestinal motility.