Atoms and Molecules — Science STD 9 — Question

Which of the above elements is most reactive and why?

9.72g of potassium chloride dissolves in 30g of water at 70°C. Calculate the solubility of potassium chloride at that temperature.

The difference in the mass of 100 moles each of sodium atoms and sodium
ions is 5.48002g. Compute the mass of an electron.

A student placed a gas jar containing air in the upside down position over a gas jar full of red-brown bromine vapours. He observed that the red brown colour spread upwards into the jar containing air. Based on this observation, the student concluded that it is only the bromine vapour which moves up and diffuses into air in the upper jar, the air from the upper jar does not move down by diffusion into the lower jar containing bromine vapours. Do you agree with this conclusion of the student? Give reason for your answer.

Give one use each of the following radioactive isotopes:

1. Uranium-235
2. Cobalt–60

What is an atom? How do atoms usually exist?

Suggest separation technique(s) one would need to employ to separate the following mixtures:
Mercury and water.

By which method of separation the volatile component from its non-volatile solute can be separated?

Explain how, cathode rays are formed from the gas taken in the discharge tube.

Define a compound. Give two points of evidence to show that sodium chloride is a compound.