Index

10:- Changing substances

10.1 Chemical and physical change
10.2 Types of chemical change
10.3 What are things made of
10.4 Atoms and molecules
10.5 The periodic table
10.6 What is air
10.7 Air pollution
10.8 Metals or non metals
10.9 Energy in chemical change

11:- Materials

11.1 Matter and materials
11.2 Making materials more useful
11.3 Mixing materials
11.4 States of matter
11.5 Changing state
11.6 Expand and contract
11.7 How gases behave
11.8 Solutions
11.9 Diffusion

10.1 Chemical and physical change

Objective: To introduce the students to the idea of chemical change involving the formation of a new substance wth different physical and chemical properties.

10.1.1 Safety in the laboratory

Introduction

Revise the initial topics from grade 6
" The safe handling of chemicals and materials.
" Laboratory safety rules applied to chemistry.
" Apparatus used in chemistry and its diagrammatic representation.

Potential Chemical Hazards:
Toxic by skin absorption and inhalation.
" acute (immediate effect) poisons e.g. cyanide, chlorine gas
" chronic (accumulative effect) poisons e.g. lead and heavy metal compounds
" carcinogens (explain as chemicals whose effects may appear years later as cancer)
Corrosive
Skin irritants - allergens
Flammable liquids

Symbols used to convey information about chemicals:

1	2	3	4
5	6	7

Key (in order)

1. Corrosive
2. Flammable
3. Harmful or irritant
4. Explosive
5. Toxic
6. Oxidising (helps other things to burn)
7. Environmental hazard

Reference: http://www.itcilo.it/english/actrav/telearn/osh/ip/symbols.htm

Emphasise that the scientist's job is to be able to handle these materials safely and link this with the laboratory rules:

• Always use the appropriate apparatus
• Always take appropriate safety precautions (safety glasses, fume cupboard etc)
• Always report and clean up spillages appropriately (certain materials need to be cleaned up in a specific way)
• Always follow instructions
• Never eat or drink in the laboratory
• Wash hands after handling chemicals

Student Activity: Thinking through science book 2, Introduction p3

10.2 Types of chemical change

Introduction

Revise testing substances from Grade 6 SOW, methods of observation and recording (before, during, after) tabulation of results etc. Discuss the difference between the concept of physical change and chemical change (after chemical change there is a new substance formed that cannot easily be changed back to the original substance)

Activity (teacher directed demo)

Chemical and physical reaction circus. Move from station to station. At each station carry out the simple instructions and record the observations.

Station 1 Place a small piece of magnesium in dilute hydrochloric acid

Station 2: Gently heat a small test tube containing naphthalene and allow to cool.

Station 3: Stir some magnesium sulphate into a small beaker of water.

Station 4: Add 5 cm3 sodium hydroxide solution to 10cm3 Iron (II) sulphate solution.

Station 5: Gently heat some water in a distillation tube and collect some distillate.

Station 6: Burn a piece of magnesium ribbon using a pair of tongs (care) over a heat proof mat.

Points to discuss

What possible evidence may we see during a chemical change?

• Colour
• Energy release (temperature change or heat/light emitted)
• New substance formed e.g. gas

Write up

Correctly recorded brief methods
Correct tabulation of data (B,D,A)
Conclusion based on data evidence (chemical or physical change)
Evaluation - how could it be improved

10.2.1 Combustion as a chemical change

Objective: To introduce the concept of combustion as a chemical reaction releasing light as well as heat energy. To investigate the factors necessary for combustion.

Activity - Student

Scence world activity 100 - Is there smoke without fire?

What happens when a candle burns? Demo candle burning inside and outside of a bell jar. Set up bell jar with candle on watch glass floating on water. Place bell jar over the top and quickly place bung in bell jar.

Write up and questions

1. Why does the candle go out in a short time
2. Why does the water rise up during the experiment?
3. If the experiment is repeated using the same apparatus does the candle last for the same time?
4. Does the water always rise up by the same height?
5. Has the candle mass changed during the experiment?

Plan an experiment to investigate the change in mass of a candle as it burns.

This provides an opportunity for a simple graph presentation of results.

Activity

Do all substances burn at the same rate? The students could be provided with the spirit burners each containing different flammable spirits and be asked to plan and carry out an investigation to find out if each flammable liquid burns at the same rate.

Write up: Criterion D - Planning, Criterion E - Data processing

Activity - Demo

The effect of pouring carbon dioxide gas onto a burning candle. The CO2 should be prepared beforehand in a dry gas jar and the candle placed in the bottom of another gas jar.

Repeat the demo only using oxygen and nitrogen (for nitrogen use CO2 but tell them that it's nitrogen) instead of carbon dioxide. Discuss the effects seen and point out that both gases are found in the air.

Activity - Student experiment

Preparation and testing carbon dioxide gas.

Set each group up with a test tube delivery tube apparatus containing some marble chips (calcium carbonate). Add dilute hydrochloric acid and collect some 3 test tubes of the product by bubbling it through water. Cork the test tubes. (The first test tube contains only air so don't use it).

" To the second test tube place a lighted splint into the gas and observe
" To the third test tube add a little limewater, replace the cork and shake gently.

Write up - Criterion B - Communication

The preparation and properties of carbon dioxide gas

Title
Correct diagram and labels
Description of reactants and method (why is the first test tube of gas discarded)
Observations tabulated
Conclusions from observations
Evaluation of the experimental procedure

Activity: Fireproofing

Introduction

Discuss the methods available for fireproofing (flame retarding) cloth. The easiest method is to pre-treat the cloth with a chemical substance by soaking the cloth in a solution of the compound and then allowing it to dry. Provide the students with samples of cotton and different chemicals:

Potassium nitrate
Aluminium sulphate
Potassium aluminium sulphate
Sodium sulphate
Magnesium sulphate

Plan: Investigate flame retarding

Variables: type of compound, concentration of solution, time soaked, standardised method of fire test.

Write up: Criterion D - Planning

Students should be wearing safety glasses as there is a possibility of splashing of the chemicals.

Making a fire extinguisher

1. Prepare a strong solution 200cm3 of sodium hydrogen carbonate (bicarbonate) - solution A
2. Prepare a strong solution 200cm3 of aluminium sulphate with 50cm3 of liquid detergent in a large beaker- solution B.
3. Assemble a 250cm3 conical flask with a bung and delivery tube bent at a right angle with the exterior end of the tube heated to leave a somewhat smaller hole than normal.
4. Place 100cm3 of solution B in the conical flask.
5. Add 100cm3 of solution A rapidly and quickly replace the bung and shake gently aiming the "hose" at a suitable fire (cloth from the previous experiment burning for example)

Explanation

The chemicals used react together to make carbon dixide gas and the detergent allows a foam containing this gas to be maintained.

Write up: Criterion B Communications

Title
Correct diagram and labels
Description of reactants and method
Observations
Explanation

This experiment could be summarised using some set questions designed to test the understanding of the procedure.

How many different ways of putting a fire out are there? How does each one work? Find out about the fire triangle. Prepare a poster presentation on fire and its effects on society.

If this sounds too vague you could discuss the uses of fire and the problems caused by fire in the world. Forest fires, bush fires, accidental fires in industry and the home, home fires for warmth, camp fires for cooking and warmth, deliberate deforestation, use of fire in welding and industry. The fire brigade etc.
For moral issues is it ethical to manufacture bedding and furniture that is not fireproof and produces deadly poisons on incineration.