Is Matter Around Us Pure? — Science STD 9 — Question

Comment on the following statements:

1. Evaporation produces cooling.
2. Rate of evaporation of an aqueous solution decreases with increase in humidity.
3. Sponge though compressible is a solid.

Calculate the number of sodium ions that are present in 212g of sodium carbonate.

The scientists now say that there are actually five states of matter A, B, C, D and E. The state A has a fixed volume but no fixed shape. The state B can be compressed very easily by applying pressure and state C has a fixed shape as well as a fixed volume. The state D is mixture of free electrons and ions whereas state E is named after an Indian scientist and a famous physicist.

1. Name the physical states (i) A (ii) B (iii) C (iv) D, and (v) E.
2. Name one substance belonging to state C which can directly change into vapours on heating. What is this process known as?
3. Name one substance which normally belongs to state B but whose solid form changes directly into gaseous state.
4. Name the most common substance belonging to state A.
5. Which state of matter makes the sum and other stars to glow.

In what respects does a true solution differ from a colloidal solution?

Why is heat energy needed to melt a solid? What is this heat energy called?

A certain species X has 17 protons, 18 electrons and 20 neutrons.

1. What is such a particle called?
2. What is the mass number of X?
3. What is the atomic number of X?

List the points of differences between homogeneous and heterogeneous mixtures.

Why does the temperature of a substance remain constant during its melting point or boiling point?

Which method is better for recovering sugar from sugar solution: evaporation or crystallization? Give reason for your answer.