How do you purify a salt in the lab?

In the lab, you can purify a salt through the process of recrystallisation.

Recrystallisation is a common method used to purify salts. It involves dissolving the impure salt in a minimum amount of hot water and then allowing it to cool slowly. As the solution cools, the salt will begin to crystallise out of the solution, leaving the impurities behind.

To start, you'll need to heat some water in a beaker until it's near boiling. Add the impure salt to the hot water, stirring until it's completely dissolved. The amount of water you use should be just enough to dissolve the salt when the water is hot. This is because salts are generally more soluble in hot water than in cold, so as the water cools, the salt will start to come out of solution and form crystals.

Once the salt is fully dissolved, remove the beaker from the heat and let it cool slowly. As it cools, you should see crystals of the salt starting to form. These crystals are your purified salt. The impurities should remain dissolved in the water.

After the solution has cooled completely, you can collect the purified salt crystals by filtration. Simply pour the solution through a filter paper in a funnel, and the crystals will be collected on the filter paper while the impure water passes through. After this, you can rinse the crystals with a small amount of cold water to remove any remaining impurities, then leave them to dry.

Remember, this method works best for salts that are much more soluble in hot water than in cold. If the salt is equally soluble in hot and cold water, the recrystallisation method won't be effective. Always handle hot solutions with care and use appropriate safety equipment.