Science [4 Mark Questions]

The nain postulates of Dalton’s atomic theory are:

1. All the matters are made up of extremely small particles called atoms (Greek philosopher Democritus used the same name for the smallest indivisible particles).
2. Atoms of the same element are identical in all respects (size, shape, mass and properties).
3. Atoms of different elements have different sizes and masses and possess different properties.
4. Atoms can neither be created nor be destroyed, i.e., atom is indestructible.
5. Atoms of different elements may combine with each other in a fixed simple ratio to form molecules or compounds.
6. An atom is the smallest particle of matter that takes part in a chemical reaction.

Properties of Cathode rays:

1. Cathode rays travel in straight line from cathode towards anode.
2. Cathode rays are made up of material particles which have mass and kinetic energy.
3. Cathode rays are deflected by both electric and magnetic fields. They are negatively charged particles.
4. The nature of the cathode rays does not depend on the nature of the gas filled inside the tube or the cathode used.

1. Cathode Ray Tube is a long glass tube filled with gas and sealed at both the ends.
2. It consists of two metal plates (which act as electrodes) connected with high voltage.
3. The electrode which is connected to the negative terminal of the battery is. called the cathode (negative electrode).
4. The electrode connected to the positive terminal is called the anode(positive electrode).
5. There is a side tube which is connected to a pump.
6. The pump is used to lower the pressure inside the discharge tube.

1. Prepare 5% of barium chloride (5g of BaCL in 100 ml of water) and sodium sulphatesolutions separately.
2. Take some solution of sodium sulphate in a conical flask and some solution of barium chloride in a test tube. 3. Hang the test tube in the conical flask


4. Weigh the flask with its contents. Now mix the two solutions by tilting and swirling the flask. Weigh the flask after the chemical reaction is occurred.

5. Record your observation. It can be seen that the weight of the flask and the contents remains the same before and after the chemical change.

6. Hence, it is proved that during a chemical change, the total mass of matter remains the same.

Step 1:
Write down the symbols of elements/ions side by side so that the positive radical is on the left and the negative radical is on the right hand side.

Step 2:
Write the valencies of the two radicals above their symbols to the right in superscript (Signs ‘+’ and ‘-‘ of the ions are omitted).

Step 3:
Reduce the valencies to simplest ratio if needed. Otherwise interchange the valencies of the elements/ions. Write these numbers as subscripts. However, ‘1’ appearing on the superscript of the symbol is omitted.