Question

Which of the following salt is used as a laxative?
(A) Epsom salt
(B) Blue vitriol
(C) Green vitriol
(D) Plaster of Paris

Answer 1

Hint: Laxatives are substances which can loosen stools and increase bowel movements. They are mainly used to treat and prevent constipation.
Magnesium containing agents are saline laxatives and help in increasing intestinal motility and fluid secretion.

Complete step by step answer:
Epsom salt is actually magnesium sulfate in the most common form which is magnesium sulfate heptahydrate or ${\text{MgS}}{{\text{O}}_{\text{4}}}{\text{.7}}{{\text{H}}_{\text{2}}}{\text{O}}$ . 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.
A saline laxative is a non – absorbable osmotically active substance which can attract and retain water in the intestinal lumen. It increases the intraluminal pressure which in turn mechanically stimulates the evacuation of the bowel.
Epsom salt also leads to the release of cholecystokinin and this in turn causes the increase of intestinal motility. Thus 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 is mainly used as fungicide and also to test blood for anemia. It is not used as a laxative and so option B is not correct.
Green vitriol is another name of crystalline ferrous sulphate. It is mainly used to prevent iron deficiency anemia. Oral administration of iron supplements leads to an uncomfortable side effect of constipation. Thus, green vitriol is not used as laxative. Hence, option C is not correct.
Plaster of Paris (calcium sulphate hemihydrates) is prepared from gypsum $\left( {{\text{CaS}}{{\text{O}}_{\text{4}}}{\text{.2}}{{\text{H}}_{\text{2}}}{\text{O}}} \right)$ by heating it at 373 K. At this temperature, gypsum loses water molecules and becomes $\left( {{\text{CaS}}{{\text{O}}_{\text{4}}}{\text{.}}\dfrac{1}{2}{{\text{H}}_{\text{2}}}{\text{O}}} \right)$ which is called Plaster of Paris. It is mainly used as building material and for moulding and casting decorative elements. So option D is also not correct.

Note:
- Saline laxatives may alter the fluid and electrolyte balance in the body.
- The main sites of action of saline laxatives are the small and large intestines and the onset of action is about half to three hours orally and two to fifteen minutes rectally.