Structure of the Atom — Science STD 9 — Question

When ice at -10°C is slowly heated, temperature of ice gradually increases till 0°C, the temperature of the system remains constant when the ice change into water and then further rises. Explain the observation.

The ratio of the radii of hydrogen atom and its nucleus is ~ 10. Assuming the atom and the nucleus to be spherical,

what will be the ratio of their sizes?

What is a physical change? Give two examples of physical changes.

Why does the temperature of a substance remain constant during the change of state?

On the basis of Thomson’s model of an atom, explain how the atom is neutral as a whole.

What does the diffusion of gases tell us about their particles?

What volume of ethyl alcohol and water must be mixed together to prepare 250ml of 60% volume by volume solution of alcohol in water.

What is a chemical change?
Give two examples of chemical changes.

The ‘sea water’ can be classified as a homogeneous mixture as well as a heterogeneous mixture? Comment.

Helium atom has an atomic mass of 4u and two protons in its nucleus. How many neutrons does it have?