How to Prepare Saturated Salt Solution and Obtain Pure Crystals

THEORY:

Crystals are homogenous particles having regular and definite geometric shapes. When a saturated solution of a substance is gradually evaporated and cooled, a time will come when the substance begins to appear as crystals. And this process of obtaining a substance in the form of crystals is called crystallization.

APPARATUS:

1) Beaker

2) Filter stand

3) Funnel

4) Filter paper

5) Porcelain basin

6) Tripod stand and wire gauze

7) Alroven

CHEMICALS:

Impure bazaar copper sulphate.

PROCEDURE:

i) Put approximately half a test-tube full of water in a beaker. Add small quantities of the powdered impure salt repeatedly with continued stirring till it forms a saturated solution at room temperature, a solution which refuses to dissolve any more of the salt added.

ii) Filter the solution, and collect the filtrate in a clean porcelain basin.

iii) Evaporate the filtrate for some time. As the solution gets heated up, stir well with a glass rod to avoid crust formation. When about two-third of the solution evaporates, crystals begin to appear at the edges, showing thereby that the crystallization point has been reached. In order to confirm the crystallization point, remove a drop of the solution at the end of a glass rod and cool it by blowing. The appearance of a crust on the glass rod shows that the crystallization point has reached.

iv) Remove the basin from the flame, and allow it to cool slowly at the ordinary temperature. When the basin is cool, place it on a beaker full of water. After some time, crystals will be found to form on the surface. The liquid left after crystallization is called the mother liquor.

v) Separate the crystals from the liquid by decanting off the mother liquor, and dry them carefully between pieces of filter paper or in an air oven (temp 60°80°c). Copper sulphate crystals are formed in triclinic shape.