1. SCIENCE
4.0 Properties, Applications And
Reactions Of Substances

2. CONTENTS
Wednesday, October 19,
 Introduction
 4.1.1 Evidence For The Occurrence Of Chemical Reaction
 4.1.2 Evidence For A Chemical Change
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 Activity 1: Mixing an Acid and a Base
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 Activity 2: Freezing and Boiling
 Activity 3: Burning
 Activity 4: Dissolving
 4.2.1 The Law of Conservation of Mass
 4.2.2 Dalton’s Atomic Theory
 4.2.3 Recent Discoveries About The Atom
 Isotopes
 Sub Atomic Particle
 Nuclear Model Of The Atom
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3. Wednesday, October 19,
INTRODUCTION
 Name :- Properties, Applications And Reactions
2011
Of Substances
Science, Unit - 04
 Subject :- Science
 Unit :- 4.0
 Slides :- 18
 Done By :- M.M.Aznee Ahamed
 Class :- 9F
 School :- Royal College
 Done On :- 01.07.2011
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4. 4.1.1 EVIDENCE FOR THE OCCURRENCE OF
Wednesday, October 19,
CHEMICAL REACTION
 Scientists often discover information about the world around them by
carrying out experiments. Experimenting involves not only doing
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something in the laboratory but also observing carefully what happens,
recording what is observed, and suggesting reasons to explain why
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things are happening (You studied in Grade 09 Science lesson 1).
 Observations are things or events that are noticed. A good observer
uses all the senses, not just sight
 A good scientist makes a careful record of what is observed.
 Scientists also try to explain why things happen in terms of what they
see and what they already know.
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5. Wednesday, October 19,
Reactions
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Physical Reaction Chemical Reaction
As there is no any As there is change in
chemical change, it is chemical composition, it
revisable. is irreversible
E.g. Freezing and
E.g. Burning a 5
melting or dissolving
matchstick
and evaporating.

6. Wednesday, October 19,
4.1.2 EVIDENCE FOR A CHEMICAL CHANGE
 Evolving gas,
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 the temperature changes,
a substance disappears,
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
 Forming of precipitation,
 Occurrence of color change,
 Occurrence of smell, light and Sound.
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7. ACTIVITY 1: MIXING AN ACID AND A BASE
Wednesday, October 19,
 You will need:
 t 20 ml or 4 large teaspoons of vinegar (acid)
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 t 1 small teaspoon of bicarbonate of soda (a base)
 t a small glass or plastic jar
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 t a teaspoon.
What to do:
 Place the bicarbonate of soda into the glass jar
 Slowly add the vinegar, a little at a time at first, then the rest all at once. Stir
 Question 1: Can you suggest possible reasons for any of your
observations?
 Question 2: Do you think the vinegar and the bicarbonate of soda are still
the same chemically after the experiment as they were before the chemicals
were mixed? Why do you think so?
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 Question 3: What type of reaction is this?

9. ACTIVITY 2: FREEZING AND BOILING
Wednesday, October 19,
 You will need:
 t about 200 ml of water
 t an ice cube tray
 t a small saucepan with lid
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 What to do:
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 Place half the water in an ice cube tray (you want about two ice cubes) and place
the tray in the freezer.
 Allow it to freeze overnight.
 The next day take out the ice cube tray and note the appearance of the ice.
 Place the ice cubes on a saucer and allow the cubes to warm up again.
 Note the changes that occur.
 While the ice cubes are melting place about 100 ml of water in a saucepan
and heat it until it starts to boil. Turn the heat down so that it continues to boil
gently. Observe the boiling process and record your observations.
 Place a lid over the saucepan for a minute. Take the lid off again. What is on
the lid? Once again note your observations.
 Question 1: Has the water been changed by these processes? Explain.
 Question 2: In your opinion, what has happened? 9
 Question 3: What type of reaction is this?

10. Wednesday, October 19,
ACTIVITY 3: BURNING
 You will need:
 t a candle
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 t the lid of a jar or a tin
 t matches.
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 What to do:
 Light a candle and attach it with some candle wax to the lid of a jar.
Write down your observations of the burning candle. Do not touch the
candle or try to blow it out until you have completed all your
observations.
 Question 1: Has the candle been changed by the process? Explain
your answer.
 Question 2: What type of reaction is this?
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11. ACTIVITY 4: DISSOLVING
Wednesday, October 19,
 You will need:
 t 50 ml (one half a small tea cup) of water
 t 1 teaspoon salt
 t a small saucepan with lid (and a stove)
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 t a glass jar to mix the chemicals.
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 What to do:
 Place a teaspoon of salt and the water into the jar and stir vigorously.
What happens to the salt? Make sure all the salt has dissolved.
 Now pour the salt and water into a saucepan and heat gently. What
happens to the water? What happens to the salt?
 Stop heating before your saucepan dries out completely.
 Question 1: Was the salt changed by the dissolving process? Explain.
 Question 2: If you did the same experiment with sugar would the same
things happen
 Question 3: If you kept on heating sugar what do you think would
happen?
 Question 4: Would sugar still be the same chemically after continued
heating? Explain. 11
 Question 5: What type of reaction is this?

13. 4.2.2 DALTON’S ATOMIC THEORY
Wednesday, October 19,
 All matter is composed on tiny particles called atoms
 The concept of the element is an old one.
 The Ancient Greeks believed that atoms had various shapes and that
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they combined by means of interlocking patterns and little hooks to
produce various substances (Today we know that atoms are held
together by electrostatic forces).
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 Dalton’s Atomic Theory can be summarized as follows:
 All matter is made up of small particles called atoms.
 Atoms cannot be subdivided
 Atoms can neither be created nor destroyed in chemical
reactions.
 All atoms of the same element are identical in mass, size, and
physical properties.
 The properties of the atoms of one element differ from those of all
other elements
 Atoms combine in simple whole number ratios to form
compounds
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14. 4.2.3 RECENT DISCOVERIES ABOUT THE ATOM
Wednesday, October 19,
 Not all of the Dalton’s postulates were correct.
 We know today that the atoms of a particular element do share identical
chemical properties but the atoms of a given element may differ in their
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mass (isotopes).
 We also know that atoms are not indivisible; they are composed of smaller
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particles (sub atomic particles)
 After the discovery of petroleum, scientists fond compound with complex
ratio
 E.g. Wax - C:H = 25:52
Isotopes
 Isotopes are atoms that have the same atomic number and differing mass
number.
 Isotopes always have the same number of protons (and electrons) and
differing number of neutrons.
 E.g.
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15. Atoms Atomic no. Atomic mass.
Wednesday, October 19,
O 8 16
O 8 18
H 1 1
H 1 2
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C 6 12
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C 6 14
Sub Atomic Particles
 Protons
 discovered in 1886 by the German Physicist Eugene Goldstein using a
cathode ray tube
 a proton possesses one unit of positive charge and a mass of 1.673 x 10-24g
 Electrons
 discovered in 1897 by the English Physicist J.J. Thompson
 an electron possesses one unit of negative charge and has a mass of 9.109
x 10-28g
 Neutrons
 discovered in 1932 by the English Physicist James Chadwick
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 a neutron is neutral and has a mass of 1.675 x 10-24g

16. Nuclear Model Of The Atom
Wednesday, October 19,
 The “Plum Pudding” Model
 In 1898 Thompson proposed that the atom was a sphere of
positive electricity containing most of the mass, and that small
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negative electrons were embedded in the surface. This model is
sometimes referred to as the “plum pudding” model of the atom.
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17.  The “Planetary” Model
Wednesday, October 19,
 In 1911 Ernest Rutherford designed an experiment using alpha particles
and thin gold foil - “gold foil experiment”. Rutherford was very surprised
by his finding but offered the following explanations which became known
as the “planetary” model of the atom.
 He proposed that the atom contains a very dense, small nucleus at its centre
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and that it contains most of the mass of an atom and all of the positive
charge.
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 He proposed that the nucleus contained the protons (he did not know of the
existence of the neutron at that time) with electrons orbiting around the
nucleus.
 He predicated that the nucleus contained (not yet discovered) neutral particle
because the nucleus appeared to be unusually heavy.
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18.  The nucleus is 1/10000 of the diameter of the atom itself.
Wednesday, October 19,
 The nucleus contains protons and neutrons, therefore the nucleus has
a positive charge. The amount of positive charge depends on the
number of protons.
 Electrons are found some distance from the nucleus
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 An atom is electrically neutral: #electrons = #protons
 The number of protons determines the identity of an element
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 The atomic number is a number characteristic of an element which
gives the number of protons associated with atoms of the element.
 The mass number is the number that gives the total number of protons
and neutrons present in the nucleus of an atom.
 X = symbol of the element
 A = mass number (p + n)
 Z = atomic number (p)
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19. Wednesday, October 19,
PREFERENCES
 www.launc.tased.edu.au
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 http://www.launc.tased.edu.au/online/sciences/PhysSci/pschem/change/Change.h
tm
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 www.mi.mun.ca
 http://www.mi.mun.ca/users/edurnfor/1100/atomic%20structure/sld001.htm
 www.youtube.com
 http://www.youtube.com/watch?v=J5hM1DxaPLw&feature=related
 Google Images
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