Lesson Notes By Weeks and Term - Senior Secondary 1

Standard separation techniques for mixtures III

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  4. Standard separation techniques for mixtures III

Term: 1st Term

Week: 7

Class: Senior Secondary School 1

Age: 15 years

Duration: 40 minutes of 5 periods each

Date:       

Subject:      Chemistry

Topic:-       Standard separation techniques for mixtures III

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

  1. Explain chromatography and sublimation
  2. Distinguish between pure and impure substances

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

PRESENTATION

TEACHER’S ACTIVITY

STUDENT’S ACTIVITY

STEP 1

INTRODUCTION

The teacher reviews the previous lesson on Separation techniques for mixtures

Students pay attention

STEP 2

EXPLANATION

He explains chromatography and sublimation

 

Students pay attention and participates

STEP 3

DEMONSTRATION

He distinguishes between pure and impure substances

Students pay attention and participate

STEP 4

NOTE TAKING

The teacher writes a summarized note on the board

The students copy the note in their books

 

NOTE

STANDARD SEPARATION TECHNIQUES FOR MIXTURES

  1. Sublimation is the separation of a mixture of solids in which one of it sublimes (by heating the solid mixture to turn one of the substances into vapour without going through liquid state). When mixture of iodine and sand is heated, iodine sublimes (turns into vapour directly) then cools and crystallize when it reaches cold surface

Examples of sublimable solids:

  1. Solid CO2
  2. Dry solid FeCl3
  3. Dry solid AlCl3
  4. ammonium chloride NH4Cl and Sand, SiO2
  5. Sulphur, S, and sodium chloride, NaCl

 

  1. Chromatography is a method of separating and identifying mixtures. Chromatography is used to Separate and identify mixtures of coloured substances in dyes into its components e.g Separating substances in urine, drugs & blood for medicinal uses to find out whether athletes have been using banned drugs

 

Separating Mixtures of Coloured Substances

  1. Obtain a dye sample then put a drop of the sample on a pencil line drawn on the filter paper.
  2. Then dip the paper into a solvent with the level below the spot.
  3. The dye will dissolve in solvent and travel up the paper at different speed. Hence they are separated.

 

PURE AND IMPURE SUBSTANCES

A pure substance is made up of only one substance and is not mixed with any other substance.

An impure substance on the other hand is a mixture.

 

Test for Purity

There are three major ways to determine the purity of a substance

  1. By their melting point (for solids)
  1. By their boiling point (for liquids)
  2. By chromatography

A pure solid melts completely at a definite temperature and a pure liquid boils at a definite temperature. Impurities lower the melting point of solids and increase the boiling point of liquid.

An impure liquid will boil over a temperature range and an impure solid will melt over a temperature range

A pure substance will give just one spot on a paper chromatogram

EVALUATION:    1. Write short notes on the following

  1. sublimation
  2. chromatography
  3. Distinguish between pure and impure substances

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively