Question

How soluble is potassium nitrate in water?

Answer 1

Hint: Potassium nitrate also known as saltpetre has a chemical formula $KN{O}_3$. It is a white solid that is soluble in water and is formed when sodium nitrate and potassium chloride solution undergo fractional distillation. It is widely used in gunpowder and in chemistry labs for preparation of nitric acid.

Complete answer: At room temperature, the structure of potassium nitrate is an orthorhombic crystal which converts to a trigonal system when the temperature rises to ${129}^{\circ }C$.
Ionic compounds are more soluble in water as compared to covalent compounds and potassium nitrate i.e., $KN{O}_3$ is an ionic salt of potassium ion $$(K^{+})$$ and nitrate ions $$(N{O_3}^{-})$$ and when dissolved in water, the positive side of the water dipole is attracted by $$N{O_3}^{-}$$ ions whereas the negative side of the dipole of water is attracted by $$K^{+}$$ ions. Hence it is soluble in water.
Potassium nitrate is not highly soluble in water but as the temperature increases, its solubility in water also increases. It has a tendency to absorb $0.03\mathrm{\%}$ of water in $80\mathrm{\%}$ relative humidity over $50$ days, hence it is not very hygroscopic i.e., it has a very less tendency to hold water molecules in its surroundings. The variation of solubility of potassium nitrate with temperature is shown as per following graph:

Note:
Potassium nitrate has many uses like it is widely used as gunpowder in the explosives like grenades, bombs, etc. It is also used in the production and manufacturing of cigarettes. It is also used in the food industry as a preservative for meat and other food products.