Question

How will you separate a mixture containing chalk, iodine and sodium chloride?

Answer 1

Separating a mixture of chalk or Calcium carbonate $\left({\mathrm{CaCO}}_3\right)$, Iodine $\left({\mathrm{I}}_2\right)$ and Sodium chloride $\left(\mathrm{NaCl}\right)$

Step-1: Separation of iodine

• The principle used in this step is that iodine is sublimable whereas chalk and sodium chloride is not.
• Subject the mixture to sublimation in the china dish.
• The process of conversion of a substance from a solid state into gaseous state on heating directly without converting into a liquid state is called sublimation.
• It is observed that iodine will convert from solid to vapour state and leave the mixture.
• $\mathrm{Iodine}\left(\mathrm{s}\right)\underset{\mathrm{Cool}}{\overset{\mathrm{Heat}}{\rightleftarrows }}\mathrm{Iodine}\left(\mathrm{g}\right)$
• On cooling of the vapours, iodine can be attained back in the solid state as a sublimate.
• The residue of chalk and sodium chloride is left in the china dish.

Step-2: Separation of chalk

• Water $\left({\mathrm{H}}_2\mathrm{O}\right)$ is added to the residue obtained in step-1.
• The principle involved in this step is that sodium chloride is soluble in water whereas chalk is not.
• On addition of water to it, sodium chloride gets dissolved in it but chalk remains undissolved.
• This mixture is left for sometime to settle down.
• This process of settling down of the particles that remain undissolved is known as sedimentation.
• Water containing dissolved sodium chloride is called supernatant and separated by the process called decantation.
• The residue of chalk is left behind in the beaker separating chalk from the mixture.

Step-3: Separation of sodium chloride

• The supernatant comprising sodium chloride dissolved in water is subjected to evaporation.
• The separation of sodium chloride from water is based on the fact that water can evaporate whereas sodium chloride can not.
• As water gets evaporated, solid powdered sodium chloride is left behind.

Thus, the said mixture can be separated using a combination of more than one method of separation.