Question

Q.1 Describe an activity to show that matter is made up of particles.

Q.2 Write the factors on which the states of matter depend. Describe these factors.

Answer 1

The following activity demonstrates that matter is made up of particles:

Measure out 10ml of sugar crystals in a dry graduated cylinder.
Take 500 ml of water in a beaker and mark the level of water with a marker.
Transfer the sugar crystals to the water. The sugar crystals will settle to the bottom of the beaker. Taste the water.
Stir thoroughly to dissolve the sugar crystals in water.
Note the volume of the solution and taste the solution. The volume of sugar solution is same as the volume of water taken. It tastes sweet.
The two substances taken are 500ml water and 10ml sugar.
Their total volume is = 500 + 10 = 510 ml
Volume after dissolution = 500ml

Following are the observations of the activity:

1. The sugar disappears but the sweet taste of the final solution indicates it is present uniformly in the solution.
2. The total volume of sugar solution is less than the sum of the individual volumes of water and sugar taken.

The activity indicates that the water has spaces which can be occupied by the sugar so that they form a solution that has both of them distributed uniformly. This can only be possible if matter is made up of tiny discrete particles with spaces in between them. Sugar particles occupy the empty spaces between the water particles and hence the final solution has a volume equal to the volume of water taken and a uniform sweet taste.
If the structure of matter was continuous without any empty spaces then it would not be possible for the sugar and water particles to intermingle with each other and form a solution with a sweet taste.

The factors on which states of matter depend are:

1. Temperature
2. Pressure

When the temperature of a substance is increases, the kinetic energy of the molecule constituting the substance also increases and molecules either vibrate faster at their positions (in solids) or move around with a faster speed (in liquids and gases). The energy supplied by heat overcomes the forces of attraction between the particles. If the heat energy supplied equals the latent heat of fusion then the solid is converted to its liquid form. When the energy equals the latent heat of vapourisation of a substance then the liquid form converts into gas.
When pressure is applied to a gas, the particles are brought closer to each other like in a liquid. Gas cylinders keep gases under pressure in liquid form and when they are released they convert into gaseous form. Cooking gas cylinders and cigarette lighters have gases under pressure in liquid form.