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TEACHER’S GUIDE

CHEMISTRY

TOPIC: OBSERVATIONS AND EXPERIMENTS

USEFUL TIPS:

Student’s experiments can be done in groups. Groups can be given different mixtures. Each group then carry out their own experiment, makes a write up of their procedure and presents to the rest of the class together with the samples obtained.

UNIT 1: MIXTURES AND PURE SUBSTANCES

This unit is suitable for senior one (S1)

BRIEF DESCRIPTION OF THE UNIT:

This unit deals with: Methods of separating mixtures. Methods of drying solids. Methods of determining purity of solids and liquids.

LEARNING OBJECTIVESStudents should be able to:

Define the key terms such as solution, solvent, solute, filtrate, residue, immiscible and miscible liquids, distillate, sublimation, melting and boiling points and chromatography.

Use melting and boiling points to differentiate between pure and impure substances.

Select appropriate methods for separating given mixtures. Describe appropriate methods of separating given mixtures. Perform simple experiments involving separation of mixtures.

Error: Reference source not found TIME REQUIRED: Minimum: 16 periods of 40 minutes each

MAIN CONTENT AND CONCEPTS TO EMPHASISE:

Criteria of purity: melting and boiling points for determining whether a substance is a mixture or pure.

Types of mixtures: uniform and non-uniform mixtures. Provide definitions for the following terms:

i. Solutions i.e. alloys as solid solutions and air as gaseous solution.ii. Solvent i.e. water as a universal solvent, ethanol, etc.iii. Solute.iv. Filtrate.v. Residue.

vi. Immiscible and miscible liquids.vii. Distillate.viii. Sublimation i.e. examples of substances that sublime – iodine,

ammonium salts, iron (III) chloride, aluminium chloride, etc.ix. Melting and boiling points.x. Chromatography.

TEACHING/LEARNING MATERIALS:

• Criteria for purity: Teacher demonstration experiments.

(i) Melting point: Illustrate with pure naphthalene and with a mixture

of naphthalene and a little camphor and water.

Apparatus required include, a 250cm3 glass beaker, boiling tube,

thermometer (0o -100oC), Tripod stand and a wire gauze.

(ii) Boiling points: Illustrate with pure ethanol and a mixture of ethanol

and water.

• Drying of solids: Sun drying, filter paper and drying agents (e.g.

anhydrous calcium chloride, concentrated sulphuric acid, silica gel,

calcium oxide etc).

• Apparatus required: A U-tube, wash bottle, Desiccators and oven.

TEACHER’S NOTES

METHODS OF SEPARATING INSOLUBLE SOLIDS FROM LIQUIDS• Decanting: For separating insoluble solids with heavy particles from liquids.

I.e. mixture of sand and water.• Filtration: For separating insoluble solids with fine particle from liquids e.g

mixture of chalk powder and water.• Centrifugal: For separating fluids of different densities (e.g. Cream from milk)

or liquids from solids in suspensions.

METHODS OF SEPARATING SOLUBLE SOLIDS FROM LIQUIDS• Evaporation (e.g. sodium chloride from water).• Simple distillation: Used when both solid and liquid is to recovered.• Crystallisation: For separating soluble solids from liquids by allowing them to

form crystals.• Fractional crystallisation: For separating two or more solutes with different

solubility at the same temperature form a liquid.

METHODS OF SEARATING COLOURED SUBSTANCES IN SOLUTION

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• Chromatography: Uses the difference in rates of movement of solutes over a porous medium like filter paper by a moving solvent (e.g. ink, chlorophyll, dyes, etc).

METHODS OF SEPARATING LIQUID-LIQUID MIXTURES

• Separating funnel: For immiscible liquids (e.g. Paraffin and water).• Simple distillation: For miscible liquids with boiling points widely far apart.• Fractional distillation: For separating miscible liquids with closely related

boiling points (e.g. Petrol and paraffin, ethanol and water).

METHODS OF SEPARATING SOLID-SOLID MIXTURES

• Sublimation: Used when one of the solids sublime on heating (iodine and sand).

• Magnetisation: Used when the mixture consist of a metal and non-metal (iron filing and sulphur).

• Hand picking and winnowing: Used when the solid particles of one of the solids are big (Stones and rice).

METHODS OF DRYING SOLIDS

• Pressing between filter papers.• Sun drying.• Oven drying.• Desiccators with drying agents.

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APPLICATION OF METHODS OF SEPARATING MIXTURES

• Filtration: Sewage and water treatment (stone and sand filter beds).

• Simple distillation: Production of local alcohol.

• Fractional distillation: Petroleum refinery, manufacture of spirits and separation of liquid air into oxygen and nitrogen.

• Fractional crystallisation: used in the extraction of sodium chloride (common salt) from lake Magadi in Kenya and lake Katwe in Uganda.

• Chromatography: Used in analysing chemicals e.g. plant extracts in chemotherapeutics research laboratories.

• Centrifugal: Used in clinical laboratories separate blood into cells (corpuscles) and plasma.

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TEACHER’S DEMOSTRATION EXPERIMENTS FOR SEPARATING MIXTURES

FILTRATION Illustrate with a mixture of chalk powder and water. Apparatus: Filter funnel, Filter paper and a conical flask.

DECANTING Illustrate with a mixture of sand and water. Apparatus: Two beakers.

CENTIFUGAL Illustrate with a mixture of chalk powder and water. Apparatus: A centrifuge and beaker.

SIMPLE DISTILLATION

• Illustrate with a mixture of sodium chloride and water( common salt).• Requirements: simple distillation kit, running water and heat source.

FRACTIONAL DISTILLATION• Illustrate with a mixture of ethanol and water.• Requirements: Fractionating column , simple distillation kit, running water

and heat source.

SEPARATION OF IMMISCIBLE LIQUIDS• Illustrate with a mixture of paraffin and water.• Apparatus: Separating funnel and a conical flask.

CHROMATOGRAPHY

• Illustrate with black ink. • Requirements: Filter paper, beaker and water.

EVAPOURATION

Illustrate with sodium chloride solution. Requirements: Evaporating dish and heat source.

CRYSTALLISATION Illustrate with sodium chloride solution. Requirements: Evaporating dish, filter papers, filter funnel, conical flask ,a

beaker and heat source.

SUBLIMATION Illustrate with a mixture of iodine and sand. Requirements: Evaporating dish, filter funnel and heat source.

MAGNETISATION Illustrate with a mixture of copper powder and sulphur powder. Requirements: Magnets.

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STUDENTS’ EXPERIMENTS

Ask students to conduct simple experiments to bring out the concepts of uniform and non uniform mixtures, miscible and immiscible liquids, soluble and insoluble solids, solute and solvent. For instance, by asking students to mix the following:

i. Sand and water. ii. Sodium chloride and water.iii. Paraffin and water.iv. Alcohol and water. v. Iron and sulphur.

Additional students’ experiments may include:

i. Filtration: Filter muddy water using filter paper and various materials as filter paper( e.g. cotton wool, cotton cloth, grass etc ).

ii. Distillation: Distillation of local alcohol.iii. Separating funnel: Separation of a mixture of cooking oil and water.iv. Sublimation: Separation of a mixture ammonium chloride and sand.v. Evaporation: copper (II) sulphate solution.vi. Crystallisation: Copper (II) sulphate crystals from copper (II) sulphate

solution.vii. Chromatography: Chlorophyll using ethanol as solvent.viii. Magnetisation: Separation of a mixture of iron filing and sulphur.

EXTENSION WORK AND STUDENT’S PROJECTS

Ask students to perform individual projects on decanting, filtration, distillation, crystallisation and chromatography.Decanting

Extraction oil from seeds: Roast, pound, grind, boil with water until oil floats then decant off the oil.

Filtration Prepare sand filter beds. Make filter funnels from plastic bottles and large leaves.

Distillation Model distillation kit using clay. Distil local alcohol.

Crystallisation

Growing of copper (II) sulphate crystals. Chemical forest made growing crystals of different chemicals in glass water.

Chromatography Analysis of dyes in coloured sweets, sodas and a mixture of phenolphthalein

and methyl orange indicators.

STUDY TOUR

Arrange to carry out class study tours to the following facilities: • Filtration: National water and sewage treatment plants ( e.g. Bugolobi sewage

treatment plant and Gabba water treatment plant in Uganda).• Distilleries: Uganda distilleries Luzira- Kampala and Kenya petroleum

refinery Mombasa.• Chromatography: Chemotherapeutic research laboratories( e.g.

Chemotherapeutics research laboratory Wandedeya- Kampala Uganda• Centrifugal: Clinical laboratories( e.g. In hospitals).

ICT APPLICATION

Use animation capabilities to show separation of a mixtures of red, blue, green, and yellow dyes by chromatography.

REFERENCES: Form One Chemistry by Patel. Complete Junior Chemistry by Atkinson New Certificate Chemistry by Holderness and Lambert. ’O’ Level Chemistry for East Africa by M.C. Sinclain. Key Science by Eileen. GCSE Chemistry First Examination By Blackie.

WEB LINKS

• GCSE Chemistry Notes on Elements, compounds, separation. http:/www.wpbschoolhouse.btinternet.co.uk/page01/EleCpdMix/EleCmdMix.htm

• Separation process. http://en.wikipedia.org/wiki/separation_ process• Separation of mixtures and chromatography.

http://www.800mainstreet.com/e3/e3.html # top• Separation of mixtures and compounds. http://www.iit.edu~smile/

ch9130.html• GCSE Chemistry mixtures- Definition-Separation-Physical

http.//www.gcsescience.com/e4.htmlSeparation of mixtures. http://dbhs.wvsd.k12.ca.us/webdocs/matter/2.6 SeparationofMixtures.html

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STUDENTS’ EXERCISES

1. Name one method that can be used to separate the mixture of the following

substances;

(i) Sodium chloride and chalk powder

(ii) Coloured dyes in sun –sip straw berry drink.

(iii) Sodium chloride and aluminum chloride

(iv) Petrol and water

(v) Paraffin and diesel

(vi) Iron filings and ash.

(vii) Copper(II) oxide and copper(II) sulphate

(viii) Copper(II) sulphate and water.

2. Name two drying agents that are used to dry substances.

3. Explain how you can separate a mixture containing sodium chloride,

ammonium chloride and chalk powder.

4. State the difference between the following:

(i) Solute and solvent

(ii) Miscible and immiscible liquids

(iii) Filtrate and distillate

(iv) Melting and boiling point

5. The picture above shows a local distillation set up.

(i) What is the role of the copper tube?

(ii) State why the tube is made of copper and not plastic?

(iii) Why is the tube coiled in the middle?

6. Name separation apparatus you can see in the pictures below.

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. What is the effect of impurity on melting and boiling points of substances?

ANSWERS TO STUDENTS’ EXERCISES

1. (i) Filtration then evaporation of the filtrate.

(ii) Chromatography

(iii) Sublimation

(iv) Use of a separating funnel

(v) Fractional distillation

(vi) Magnetism

(vii) Dissolving in water, filtration and crystallisation

(viii) Crystallisation

2. Concentrated sulphuric acid and anhydrous calcium chloride.

3. The mixture is first heated where the ammonium chloride comes off as a

vapour (sublimes). The remaining mixture of sodium chloride and chalk is now

then shaken with water to dissolve all sodium chloride. The mixture is then

filtered. The filtrate which is sodium chloride solution is then evaporated

carefully on an evaporating dish. The residue is chalk.

4.

i. The solute is the substance that dissolves in a solvent.

ii. Miscible liquids have a homogenous layer while immiscible liquids

are separated by a clearly defined boundary.

iii. Filtrate is a clear solution or substance obtained by the filtration

process while a distillate is a condensed liquid obtained by

distillation process.

iv. Melting point occurs at lower temperature than boiling point.

Melting point is defined as the temperature at a solid substance

changes to liquid state at atmospheric pressure. Boiling point is the

temperature of a vapour of a substance boiling at atmospheric

pressure.

5. (i) To convey alcohol vapour from the drum to the collection point.

(ii) It is resistant to decomposition by heat.

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(iii) To increase the surface area for condensation of the alcohol vapour.

6. Distillation and centrifuge.

7. Impurities decrease or increase melting and boiling points.

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