TOPIC: Chemical Reactions vs Physical Phenomena
METHOD: Practical – Ss work in groups
AIMS OF THE LESSON:
- Ss understand such things as: substance, element, compound, mixture, physical
phenomenon, chemical reaction
- Ss can divide substances,
- Ss can tell differences between a mixture and a compound
- Ss can recognize changes (physical and chemical)
- Ss can write down simple chemical reactions, Ss can recognize reactants and products
DIDACTIC HELP:
- substances and mixtures
- tasks for Ss
LESSON
INTRODUCTION
1. Aims of the lesson
2. Ss are told what they are going to do during this lesson
I CHEMICAL SUBSTANCES AND THEIR MIXTURES
What are chemical substances?
How can we divide substances and their mixtures?
SUBSTANCES
SIMPLE SUBSTANCES
COMPOUND SUBSTANCES
ELEMENTS
COMPOUNDS
METAL
MIXTURES
NON-METAL
HOMOGENOUS
HETEROGENOUS
Task1.Divide the following substances into groups:
magnesium, sulphur, copper, magnesium oxide, iron sulphide, granite, water with sugar,
sulphur with iron dust, carbon dioxide
METAL
ELEMENTS
NON-METAL
COMPOUNDS
MIXTURES
HOMOGENOUS HETEROGENOUS
II. PHYSICAL PHENOMENA AND CHEMICAL CHANGES
Experiments
Ss prepare pictures related to experiments, we write down observations and conclusions
together
Experiment 1. We prepare a mixture of iron and sulphur
Observation : Iron filings and sulphur powder form a mixture, its constituents can be
distinguished with the naked eye. The constituents of the mixture separate when magnet
attracts iron filings.
Conclusion: Constituents of such a mixture do not change their properties when separated.
Experiment 2. Sublimation of impure iodine ( separation of a mixture of sand and iodine)
Cold water
iodine crystals
mixture of
iodine and sand
Observation: Iodine is in a constant shape in room temperature and it is a lustrous substance,
it’s blue and black. Iodine when heated sublimates and it gives violet fumes which have
irritating smell. Iodine fumes solidify when they contact something cold. It’s a process of
resublimation. The sand that impures iodine remains at the bottom of the beaker.
Conclusion: The process doesn’t change the iodine properties. We get purified iodine without
sand.
Task 3. Burning magnesium in oxygen (Caution – dangerous flame)
Observation: Magnesium is burning with a light luminous flame and white powder appears
Conclusion: Magnesium burning is a chemical reaction (burning is a violent process of
oxidation, substance is combining with oxygen). The reaction scheme:
2Mg +
O2
→
2 MgO
MAGNESIUM + OXYGEN →
MAGNESIUM OXIDE
Reactants
Product
Reagents
What is a physical phenomenon?
It’s a process in which constituents have their own properties e.g. mixture forming, melting,
sublimation.
What is a chemical change?
New substance occurs in result of chemical reaction, it has different properties than reagents
e.g. magnesium burning.
How do we call substances that take part in a chemical reaction?
How do we call substances that appear in result of the reaction?
Homework
Below there are physical and chemical changes:
- combustion of sulphur in oxygen
A)
B)
C)
making oxygen out of mercury oxide (II)
condensation of nitrogen
combustion of magnesium
water vaporizing
warming copper in the flame of a blowpipe
boiling of water
underline chemical reactions
write down the reactions
point reactants and products