Lesson 1–3: The Properties of Matters and their Classification
We have to use various materials in doing different works. We use thousands of materials, starting with the water to wash our hands and face just after getting up from bed in the morning. We use various types of food, crockery, clothes, toy, stone, cycle, football, marble, book, etc. Of these, some are soft, some are hard, some are shiny, some are round and some are flat. But all of them are matters. All of these materials occupy space and have mass. So, we can say that things which occupy space and have mass are called matters. However, the volume of some very small particles of matters is negligible.
There are numerous types of matters in the world and they are classified in various ways. Among these, one of the classifications is based on the state of the matter. Let us take an example. When a piece of ice is kept in a pot, what happens? It is converted into water. Again we can convert the water into vapour by heating it up. So, it appears that water can be found in three different states, e.g., ice, water and vapour. When water remains in the form of ice, it is in solid state. When it remains water, it is in liquid state. Again when it becomes vapour or steam, it take gaseous state. So, matters are divided into three groups depending on their states.
Matter
- Solid
- Liquid
- Vapour or Gas
Now the question is what characteristics are responsible for making a matter solid, liquid or vapour?
A solid body has a definite shape. The space occupied by a body is its volume. As all solid bodies occupy space, they all have volumes. The size and volume of a solid body can't be changed easily. It is highly rigid, that is, it has rigidity. Although some of the solids have less rigidity (for example: mustard seed, boiled rice, banana).
A liquid has no definite shape. It holds the shape of the container where it is kept. Liquid has a definite volume, because it occupies space like solid. Its volume can also be measured. Does this volume change? No, although depending on the shape of the container the shape of the liquid changes.
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The volume remains the same. As a liquid has no definite shape, its shape is changeable. Therefore, it can be said that the liquid is not rigid like solid, e.g., liquid has no rigidity.
Let us take the example of air to understand the property of gas. Like air a gas has no definite shape. Is there any definite volume of a gas? Think of two cylinders, one small and another large. Now if you keep the same amount of gas in both the cylinders, the gas will occupy the entire space of the small cylinder as well as of the large cylinder. Then it can be said that when the same amount of gas is kept in a small cylinder, its volume is small and if it is kept in the large cylinder, its volume is large. That means, the volume of the gas is the volume of the container in which it is kept. So gaseous matter has no definite shape and volume. There is no rigidity at all.
In addition to that, some other characteristics which can be taken into account for classifying matters are density, rigidity, flexibility, thermal conductivity and electrical conductivity.
Task: Collect the following things from your house and school.
Chalk, pencil, note book, rubber, duster, hammer, pin, soap, spoke of cycles, wheel, cricket bat, safety matches, salt, glass, plate of aluminium, school bell, etc. Classify the matters which are made of paper, wood, metal and which are not made of any of these materials. Also, classify them considering which one glitters and which one does not.
Rigidity and Flexibility
Some matters are soft, some are hard; some are flexible and some are non-flexible. Do the task below to know about these things.
Task:
Take a pot of aluminium, one piece of rubber, one piece of wood, a candle, one piece of stone and a nail. Scratch them with a metal key and observe what happen. Which one can be scratched easily and which one cannot be scratched so easily. Take each of them between two fingers and apply pressure. You will see that some of them are flexible while some are hard and inflexible. Also, find that others of these things have rough surfaces while others are smooth and some others are breakable.
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Now make a table like the one shown below.
| Name of the substance | hard | soft | flexible | inflexible |
|---|---|---|---|---|
| 1. | ||||
| 2. | ||||
| 3. | ||||
| 4. | ||||
| 5. | ||||
| 6. |
Matters can be divided into different types based on their density. But it is seen that metals have the highest density among all solids. In the next lessons we will discuss some more properties of matter.
Lesson 4–6: Properties of Metals and Non-metals
Based on their different properties, matters are classified into two types: metals and non-metals. Now, we will learn about some characteristics of metals and non-metals.
Metals:
We use various types of aluminium pots, gold jewellery, electric wire made of copper for many purposes. How do these matters look like? They all shine or glitter. This is a common characteristic of most metals.
On the other hand, we use aluminium pots or iron pans for cooking. Why? Because they transmit the heat from the oven fire to the main ingredients of cooking (rice, fish, etc.) and the ingredients get boiled due to that heat. Hence, another characteristic of metals is, they conduct heat very well. So, metals are called good thermal conductors.
Again, what is the cause of the use of copper for electric conductivity? To Metals are good electric conductors of electricity. So, we can say that metal or metallic matters are shiney, and they conduct heat and electricity.
Non-metal:
Can you tell how gases such as nitrogen, oxygen or hydrogen look like? You will not be able to answer this question because these gases neither glitter like metals nor they have any visible feature to mark. Again, they do not conduct heat or electricity like metals. So, non-metals are called non-conductors or insulators.
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Task: Take magnesium ribbon, zinc-plate and scales made of plastic, wood and steel scales and keep them in the sun one after another. Observe which of them glitter and which do not. Write down the findings of your observation in the table below.
Table
| Name of the Matter | Property |
|---|---|
Task: To observe the thermal conductivity of a metal (copper)
Required Accessories: Thick copper wire (20 cm), two pieces of cork, safety matches, candle or spirit lamp.
Procedure: Insert the copper wire carefully through the cork so that the cork remains in the middle of the wire.
Light the candle. Now, holding one end of the wire, place its other end on the candle-flame. In this way, hold the wire until your hand does not feel warm (hot).
Fig. 7.1 Thermal conductivity of a metal
Here, what is the reason of using the cork? It is used so that the heat from the flame cannot reach directly to the hand. Why do you feel the heat at the end of the copper wire that you are holding in your hand? One end of the wire receives the heat from the flame and it travels to your other end because copper is a good conductor of heat. If it was not so, you may not have felt the heat. Therefore, it is proved by this experiment that copper is a good thermal conductor. In fact, all metals conduct heat like copper. That is why metals are used where thermal conduction is essential (for example: in refrigerator, air conditioner, solar panel, etc.). Therefore, it is our moral duty to ensure proper uses of metals as well as to avoid wastage of them.
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Task: Observing the thermal conductivity of various matters
Required accessories: 1 glass-spoon, 1 plastic-spoon, 1 aluminium-spoon, 3 one taka coins, 1 beaker of 600 mL, 300 mL water, a spirit lamp, wax, safety matches and stop-watch.
Procedure: Make the wax soft by heating it moderately. Add a little soft wax on the handle of each spoon. Now, place the coins on the wax with pressure so that the coins get stuck on the spoon. Take about 300 mL water in the beaker and put it on the spirit lamp. Now, immerse the three spoons in the beaker by holding them with threads in such a way that the coins stay outside the upper portion of the beaker. Light up the spirit lamp and continue to heat the beaker. Carefully observe the coins. Use the stop watch to record the time to determine the time taken by each coin for being separated from the spoon.
Fig. 7.2 Thermal conductivity of various matters
From which spoon do the coins get separated at first and from which it happened last of all? Why are the coins separated? Undoubtedly, the coin on the aluminium spoon is separated at first because the aluminium is a good conductor. So, heat from the hot water in the beaker reaches the wax of aluminium spoon comparatively faster through conduction. As a result, the wax melts down and the coin is separated. On the other hand, as the thermal conductivity of plastic is the least among the three, the heat from the hot end of the plastic spoon transmits slowly to the cold end that is towards wax due to conduction. As a result, it takes a longer time to melt the wax and the coin on it is separated last of all. Again, thermal conductivity of wood is less than aluminium but greater than plastic, so heat reaches the wax on wood faster than plastic but slower than aluminium. As a result, the time taken to separate the coin from the wax of wooden spoon is more than aluminium but less than plastic.
Lessons 7–8: Electrical Conductivity of Metal and Non-metals
You have known earlier that metals are generally electric conductors and non-metals are electric non-conductors or insulators. Now, you will see yourself how metals act as electric conductors and non-metals act as electric non-conductors.
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Task: Observation of electrical conductivity of metal
Required Accessories: One electrical cell (battery), one electrical bulb, 2 electrical wires, 1 spoon, piece of aluminium, rubber, wood, plastic spoon.
Procedure: Take the electric cell and see that there is a positive (+) sign at one end and a negative (-) sign at the other end. Connect one copper wire at one end of the cell and another copper wire at the other end of the cell (as in the fig.). One of you take the bulb. You will see two raised metallic points or thick wire like points at one end of the bulb which end is supposed to go into the socket. Now, connect the open end of one wire with one of the connecting points of the bulb and connect the other wire with another connecting point.
Fig. 7.3 Electrical conductivity
What do you see? The bulb is illuminating. As copper is an electric conductor, it transmits electricity taking from the cell and send it to the bulb. For this reason, the bulb lights up. If the copper wire was not an electric conductor, it could not conduct electricity, and the bulb would not illuminate.
Now, disconnect the copper wire and give connection between them with an iron or aluminium wire. See what happens? Next, connect the two wires by a piece of wood, plastic, rubber, etc.
Is the electric bulb on now? No, it is off. Since rubber, plastic and piece of wood—all these are electric non-conductors, they cannot conduct electricity from the cell. That's why the bulb has not illuminated.
Lesson 9–10: Melting Point and Boiling Point
Task: To know about the melting point of a solid
Required Accessories: 1 beaker, wax, thermometer, test tube, spirit lamp etc.
Procedure: Take some small pieces of wax in the test tube. Taking water in the beaker and keep it on the spirit lamp, immerse the test tube and the thermometer in the water of the beaker so that none of them touches the bottom or wall of the beaker with the help of a stand (as shown in the figure). Apply heat to the bottom of the beaker with the help of the spirit lamp.
Notice the thermometer reading and the wax in the test tube. Is the temperature of the thermometer increasing? Is there any change of the state of the wax? Observe carefully the condition of the wax when the temperature of the thermometer reaches nearly 57 degree Celsius.
Fig. 7.4 Determination of melting point
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Is the wax melting? When the wax starts to melt, notice the temperature in the thermometer. What is the reading of this temperature? Is it 57 degree Celsius? Then 57 degree Celsius is the melting point of the wax. So, (at standard pressure) the temperature at which a solid begins to melt is known as its melting points. Like wax, each solid has its melting point. Now, determine the melting point of ice.
Boiling Point
When you take some water in a beaker and continue to heat it, what happens? The temperature of water increases and at a certain temperature it begins to boil. The temperature at which water begins to vaporise is called the boiling point of water. Like water, a liquid has its specific boiling point. Let us determine the boiling point of water.
Task: To determine the boiling point of water
Required Accessories: One beaker, water, thermometer, spirit lamp, etc.
Procedure: Take a beaker with half of it filled with water. Put the beaker on the spirit lamp. Immerse the thermometer in the water in the beaker as shown in the figure. Now, apply heat and observe the temperature in the thermometer. When the temperature of the thermometer raises to 95 degree Celsius, carefully observe the condition of water in the beaker.
Fig. 7.5 Determination of the boiling point
When the water begins to boil, notice the temperature in the thermometer. This temperature is the boiling point of water. What is the reading of this temperature? It is 100 degree Celsius. You can determine the boiling point of ether or spirit. But as the organic substances are combustible, you cannot apply heat directly to them. You need to take an aluminium pot with water and heat the beaker with ether or spirit in it.
Change of metal and non-metal when it is strucked:
Task: Observation of the change of metal and non-metal applying strike
Required Accessories: Iron plate, copper pot, one hammer
Procedure: Take the iron pot on one hand and strike it with a hammer by another hand. What happens? It creates a jingling sound. Will it be broken when struck? No, it will not. Similarly, take the copper pot and strike it with the hammer. What happens? Now take some pieces of sulphur and carbon and strike them with the hammer and observe.
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As the iron and copper plates are striken with the hammer, they create jingling sounds and do not break down easily when they are stricken. That means metals are not easily broken. On the other hand, sulphur and carbon will get broken and will not create jingling sounds.
Precaution: Use security spectacle and hand gloves so that sulphur or pieces of charcoal do not enter the eyes or come to contact with your hands.
Freezing Point
We light candles on birth-day parties or when the electricity goes off. What happens in this case? A portion of wax burns to give light and another portion of wax melts down due to heat and falls along the body of the candle which after some time (loss heat) freezes and converts to solid wax again. The process of changing from liquified wax to solid wax is known as cooling. This may happen to all other liquids too.
Task: Determination of the freezing temperature
Required Accessories: 1 test tube, 1 beaker, 1 stand, some wax, water, 1 thermometer, spirit lamp, wire-net, tripod and clamp.
Procedure: Take some wax in the test tube. Fill up the three fourth portion of the beaker with water. Keeping the wire-net over the tripod, place the beaker upon it. Immerse the test tube in the water of the beaker as shown in the figure. Continue to apply heat on the bottom of the beaker by spirit lamp till the wax completely melts down. Now, immerse the thermometer in the test tube so that the lower part of it remains dipped in the melting wax. Remove the test tube with thermometer from the beaker then hold it by the clamp in the stand. Clean the test tube by tissue paper. Observe the temperature of the thermometer. See the temperature at the moment when the wax begins to freeze.
Fig. 7.6 Determination of the freezing point
At what temperature does wax begin to freeze? Is it 57 degree Celsius? Yes, that is correct. This temperature that is 57 degree Celsius is the freezing point of wax. Earlier you got the melting point of wax as 57 degree Celsius.
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That means the melting point and the freezing point of a matter are the same.
Now, tell us what is the freezing point of water? Zero degree Celsius? Then the melting point of water (in the form of ice) should also be zero degree Celsius.
If the temperature of a matter remains beyond its freezing point and if it is greater than the surrounding temperature, then if the matter is kept in the surrounding temperature, it losses heat slowly. As a result, its temperature decreases and when the temperature comes to the freezing point, it changes to solid state, as it happened in case of wax. When the wax was in liquid state, its temperature was more than 57 degree Celsius. When the test tube with wax was brought outside, it emitted heat slowly. As a result, the temperature decreased. It was decreasing in this way to reach the freezing point, e.g., 57 degree Celsius, and then the wax got frozen to become solid.
Topics we have learnt in this chapter are:
- Objects which have mass and which occupies space are matters. Matters are of three states- solid, liquid and gaseous.
- Solid has a definite shape, volume and rigidity. Although there is a definite volume of a liquid, it has no definite size and rigidity.
- Vapour or gas has none of the definite shape, volume (shape) or rigidity.
- Fundamental matters are of two types metals and non-metals. Metals are generally shiny. They conduct heat and electricity and create jingling sounds when struck.
- Non-metals do not generally glitters. These do not conduct heat and electricity and do not create jingling sounds when struck.
- The temperature at which a solid begins to melt is known as its melting point. The melting point and the freezing point of a substance are the same.
- The temperature at which a liquid begins to vaporise is called the boiling point of the liquid.
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