medium difficulty5 min

Separation by Sublimation and Filtration

Sublimation separates a sublimable solid from non-sublimable impurities, while filtration separates an insoluble solid from a liquid using a filter.

In one line: Filter stops insoluble particles; sublimation lifts sublimable solids as vapour.

Practice This Concept

Understand it

The correct separation method depends on the properties of the components. If one solid changes directly into vapour on heating, sublimation can separate it. If an insoluble solid is mixed with a liquid, filtration can remove the solid residue from the liquid filtrate.

Example

Ammonium chloride can be separated from sand by sublimation, while sand can be separated from water by filtration.

Rule to remember

Method rule: sublimable solid plus non-sublimable solid needs sublimation; insoluble solid plus liquid needs filtration.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

1To separate ammonium chloride and common salt, heat the mixture gently under an inverted funnel.
2Ammonium chloride sublimes and deposits on cooler funnel walls, while common salt remains behind.

Method you can reuse

1List the components.
2Mark each as soluble, insoluble, sublimable, or non-sublimable.
3Match the property to the method.
4Write what remains as residue and what is collected.

Visual tip

For sublimation, show china dish, inverted funnel, cotton plug, and deposited solid on funnel walls. For filtration, show filter paper, residue, and filtrate.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why can sand be separated from water by filtration but salt cannot?

Think first, then show answer

Sand can be separated by filtration because it is insoluble and remains as particles, but dissolved salt passes through the filter with water.

Common wrong answer

Using filtration for salt solution.

Why it loses marks: Dissolved salt particles pass through filter paper along with water.

Don't mix this up

Students often write filtration for any mixture without checking whether the solid is dissolved or insoluble.

Exam tip

First identify whether the component is sublimable, soluble, or insoluble; then choose the method.