Matter in Our Surroundings — Science STD 9 — Question

Define vapourization.

The atomic number of an element X is 16.
What will be the valency of X?

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

Verify by calculating that:
5 moles of CO₂ and 5 moles of H₂O do not have the same mass.

Define:

1. Solute
2. Solvent

Name the elements water is made of. What are the valencies of these elements? Work out the chemical formula for water.

Give reason:

1. Plasma is found in the stars. 
2. The molecules of a solid have the strongest intermolecular forces.

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.

1. Compare the properties of solids, liquids and gases in tabular form.
2. Give two reasons for saying that wood is a solid.

During class, the students resemble molecules in a solid (because they are very close to one another)

While going from one classroom to another the students resemble molecules in a liquid (because they are a little more father apart from one another)

What is meant by the symbol of an element? Explain with examples.