Question

A student took about 50 mL of water in a glass beaker. He added a small amount of potassium nitrate (nitre) and stirred it with a glass rod. It immediately dissolved. Keeping the temperature constant, he kept on adding salt to the water. After some time, it did not dissolve anymore and settled at the bottom of the beaker. He then raised the temperature and the salt settled at the bottom and dissolved again.

1. Why did potassium nitrate dissolve in water?
2. When the salt gets settled at the bottom of the beaker, what is the nature of the solution called?
3. What happened when the beaker was heated?
4. Can we recover potassium nitrate from the solution?

Answer 1

1. Potassium nitrate dissolves in water because it is an ionic compound that on getting dissolved in water breaks into ions. Moreover, particles of potassium nitrate occupy the spaces between the particles of water so they completely dissolve in water.
2. When the salt gets settled at the bottom of the beaker, the nature of the solution is called a saturated solution. No more solute can be added to this solution as it will start settling down at the bottom.
3. When the beaker was heated the salt started dissolving in the water and the solution became unsaturated where more solute (salt potassium nitrate) can be added to the solution.
4. Yes, potassium nitrate can be recovered from the solution by crystallization technique. The solution of potassium nitrate is filtered and allowed to cool so that the crystals of the salt get separated in the form of crystals.