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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.

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Student-friendly explanation

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.

How to write this in exams

  1. 1

    Start with the exact idea

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

  2. 2

    Then show how to use it

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

  3. 3

    Add one concrete example

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

  4. 4

    Avoid this incomplete answer

    Using filtration for salt solution is wrong because dissolved salt particles pass through filter paper along with water.

Definition

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

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.

Memory hook

Filter stops insoluble particles; sublimation lifts sublimable solids as vapour.

Examples and method

Worked example

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

Method to apply

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

Diagram support

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

How CBSE asks it

Questions give a mixture such as sand-water or ammonium chloride-salt and ask for the suitable separation method with reason.

Avoid common mistakes

Common confusion

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

Common wrong answer

Using filtration for salt solution is wrong because dissolved salt particles pass through filter paper along with water.

Exam tip

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

Quick check

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

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

Study the separation by sublimation and filtration diagram carefully

Use the labelled diagram to keep separation by sublimation and filtration clear in short answers and revision.

What this diagram makes clear

This diagram keeps the labels and direction of separation by sublimation and filtration in the right order.

Where this helps in exams

Use this for labelled diagram work and short exam answers on separation by sublimation and filtration.

Revision cue

Revise separation by sublimation and filtration through the labels before writing the answer.

Answer writing and exam use

1-mark answer

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

2-mark answer

Sublimation separates a sublimable solid from non-sublimable impurities, while filtration separates an insoluble solid from a liquid using a filter. Method rule: sublimable solid plus non-sublimable solid needs sublimation; insoluble solid plus liquid needs filtration. Ammonium chloride can be separated from sand by sublimation, while sand can be separated from water by filtration.

3-mark answer

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. Method rule: sublimable solid plus non-sublimable solid needs sublimation; insoluble solid plus liquid needs filtration. To separate ammonium chloride and common salt, heat the mixture gently under an inverted funnel. Ammonium chloride sublimes and deposits on cooler funnel walls, while common salt remains behind. Questions give a mixture such as sand-water or ammonium chloride-salt and ask for the suitable separation method with reason. Using filtration for salt solution is wrong because dissolved salt particles pass through filter paper along with water.
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