The 9th lesson from the 5th std science text book is about the particulate form of matter. It explains how all substances are made up of minute particles. The lesson also elaborates on the concept of matter as something that occupies space and that has mass. Let us see how these scientific concepts may be explained to students with the aid of some simple experiments.
Experiment 1 :
Materials: 1 porcelain tile, I beaker for water, I spoon, 2 glass beakers (250 ml and 100 ml respectively) sugar cubes, granulated (regular) sugar, powdered sugar
(This experiment is carried out while asking the students relevant questions.)
Practical:
-This beaker has water. Is water a substance?
-Yes
-Can you see or identify the particles of water?
-No.
-So does this mean that water does not have any particles?
-Is that possible?
-There must be particles in water.
-What then can you deduce from this observation?
-That the water particles cannot be seen with the naked eye. They are very minute.
-There is air all around us. Can we see the particles of air?
-No.
-Then how do we know that they are present or that the air is present? We can feel the air if we shake the book in our hands. When the particles in air start moving, they create a wind or breeze.
-So we can deduce that the particles of air are also too minute to be seen with the naked eye.
-Now look at the three kinds of sugar placed on the tile. Some are big pieces, some are smaller, while the powdered sugar bits are very tiny.
-Let us now put these three types of sugar into this 100 ml. beaker* full of water, and dissolve them in the water.
-So now that all the big and small bits of sugar have disappeared, does that mean they are no longer present?
-No.
-In fact the water has turned sweet, which indicates that the sugar particles are now in the water.
-So sugar particles too are so minute that they cannot be seen with the naked eye.
-We may infer that substances have particles that are not visible to the naked eye.
-Shall we try and think about this observation from a different angle?
-What is this solid lump of sugar made up of? The sugar particles are all stacked together, they do not change their shape, nor their size. Why is this so?
-It is because a strong force of attraction is at work between the solid particles of sugar. This keeps all the particles in their place, changing neither their shape nor size.
-Now let us pour the water from this small beaker into this bigger one. You can see how the quantity of water has remained constant, while its shape has changed.
That is because the water particles are tied together by a medium force of attraction. They may move from here to there but they stay within the boundaries of the water.
What about the particles in gas? There is almost zero attractive force among its particles, and that is why gas particles can travel in any direction and fill any volume available.
Experiment 2 :
Materials: 1 overflow vessel, 2 beakers (250 and 100 ml ), 1 aluminium block, 1 pendulum bob, 1 stone, 1 rubber balloon, 1 porcelain tile, some thread
Practical:
-This 100 ml beaker does not have any water or anything else in it. Usually we would say, “It’s empty.” But is it really empty?
-No, it is full of air.
-Let us now blow air into this balloon. Now that we have filled the balloon by blowing in air through the mouth, the balloon is full of air. So we may deduce that, in general, gases occupy space.
This 250 ml beaker has a little water. It has filled up 1/4th of the beaker. The rest of the beaker has air. Now let us pour some more water into the beaker. We can see that water has now occupied more space within the beaker. So liquids occupy space.
Let us now fill this overflow vessel with water and hold an empty beaker under it to catch the overflow. Let us place the stone inside this vessel. As you can see, some water has overflowed into the beaker. But what quantity of water will overflow? Only as much as the mass of this stone. The experiment may be repeated using the aluminum block, or the pendulum bob. So we may deduce that solids occupy space and, in general, substances occupy space.
Experiment 3 :
Materials: lumps of sugar, sugar granules, weighing scale
Practical:
-Observe this sugar granule. It is made up of sugar particles. Can you guess how many particles are there in it? No, that it is not possible. So let us call that number ‘x’.
-Now observe this big lump of sugar. It is definitely made up of many more particles than ‘x’. There could well be 10x or 12x particles in this lump.
-Is it possible to make a more exact statement? Yes, it is.
-Each and every object on this Earth is under its gravitational pull. The gravitational pull exerted on one particle will be twice as much on two particles, three times on three particles and so on.
So this means, if we can measure the amount of gravitational pull exerted on any object, we can calculate the number of particles (amount of matter) in that substance. Mass is the measure of the amount of matter within a substance.
-We can do this with the help of this weighing scale. Let us place this bag of sugar on it. The reading shows 5 gm. So that is the total mass of the object (in this case, the sugar).
Now let us add another bag. Now the scale reads 10 gm. That means when the quantity of substance increases, its mass also increases.
So we may deduce that mass is the measure of the quantity of a substance.
In this way, we can do several small, simple experiments to enable students to understand and remember the particle form of substances, or of matter.
Blog: Jayant Phalke, Vidnyanvahini, Pune
translation and editing: samata.shiksha team
Vidnyanvahini is an organisation that works to spread scientific awareness and knowledge among children in rural areas. For more information contact:020- 24222127.