SCIENCE4.0 Properties, Applications AndReactions Of Substances
CONTENTS Wednesday, October 19, Introduction 4.1.1 Evidence For The Occurrence Of Chemical Reaction 4.1.2 Evidence For A Chemical Change 2011 Activity 1: Mixing an Acid and a Base Science, Unit - 04 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 2
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 3
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 2011 something in the laboratory but also observing carefully what happens, recording what is observed, and suggesting reasons to explain why Science, Unit - 04 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. 4
Wednesday, October 19, Reactions 2011 Science, Unit - 04 Physical Reaction Chemical Reaction As there is no any As there is change inchemical change, it is chemical composition, it revisable. is irreversible E.g. Freezing and E.g. Burning a 5 melting or dissolving matchstick and evaporating.
Wednesday, October 19, 4.1.2 EVIDENCE FOR A CHEMICAL CHANGE Evolving gas, 2011 the temperature changes, a substance disappears, Science, Unit - 04 Forming of precipitation, Occurrence of color change, Occurrence of smell, light and Sound. 6
ACTIVITY 1: MIXING AN ACID AND A BASE Wednesday, October 19, You will need: t 20 ml or 4 large teaspoons of vinegar (acid) 2011 t 1 small teaspoon of bicarbonate of soda (a base) t a small glass or plastic jar Science, Unit - 04 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? 7 Question 3: What type of reaction is this?
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 2011 What to do: Science, Unit - 04 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?
Wednesday, October 19, ACTIVITY 3: BURNING You will need: t a candle 2011 t the lid of a jar or a tin t matches. Science, Unit - 04 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? 10
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) 2011 t a glass jar to mix the chemicals. Science, Unit - 04 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?
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 2011 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). Science, Unit - 04 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 13
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 2011 mass (isotopes). We also know that atoms are not indivisible; they are composed of smaller Science, Unit - 04 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. 14
Atoms Atomic no. Atomic mass. Wednesday, October 19, O 8 16 O 8 18 H 1 1 H 1 2 2011 C 6 12 Science, Unit - 04 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 15 a neutron is neutral and has a mass of 1.675 x 10-24g
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 2011 negative electrons were embedded in the surface. This model is sometimes referred to as the “plum pudding” model of the atom. Science, Unit - 04 16
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 2011 and that it contains most of the mass of an atom and all of the positive charge. Science, Unit - 04 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. 17
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 2011 An atom is electrically neutral: #electrons = #protons The number of protons determines the identity of an element Science, Unit - 04 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) 18
Wednesday, October 19,PREFERENCES www.launc.tased.edu.au 2011 http://www.launc.tased.edu.au/online/sciences/PhysSci/pschem/change/Change.h tm Science, Unit - 04 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 19