Question

How do you crystallize potassium nitrate from its aqueous solution?

Answer 1

I would assume the most straightforward way would be to create a hot, saturated solution of potassium nitrate by heating it on a hotplate until just before it reaches its boiling point. You may then filter the hot solution if neccessary (using a warm funnel and conical flask) in order to remove any insoluble impurities in the solution. Then, leave the remaining filtrate in the flask to cool slowly in an ice bath to allow crystallisation to occur.

You may also need to try and scrape the inside of the beaker/conical flask with a glass rod in order to induce crystallisation, but the longer and more progressive the cooling back down to room temperature, the better and purer the yield of crystals.

The crystals formed inside the flask can be separated from the filtrate using a Buchner flask and funnel (i.e. under vacuum) to form the potassium nitrate crystals, which can then be dried.

We can repeat this technique with the filtrate we collect if we feel that there is still some uncrystallised product present and we want to improve our yield of crystals.

Answer 2

thank you very much!

Answer 3

No problem @Lily :)