Matter in Our Surroundings — Science STD 9 — Question

Calculate the number of moles present in a drop of chloroform (CHCl₃) weighing 0.0239g.
(Atomic masses: C = 12u; H = 1u; Cl = 35.5u)

How will you separate a mixture of cooking oil (groundnut oil) and water?

The substance X normally exists in a physical state which can flow easily but does not fill its vessel completely. It also turns anhydrous copper sulphate blue. When substance X is cooled excessively, it changes into a substance Y which has a fixed shape as well as a fixed volume. If, however, the substance X is heated strongly, it changes into a substance Z which has neither a fixed shape nor a fixed volume.

1. Name the substances (i) X (ii) Y and (iii) Z.
2. What is the process of conversion of X into Y known as?
3. At which temperature X gets converted into Y?
4. What is the process of conversion of X into Z known as?
5. At which temperature X gets converted into Z?

Alka was making tea in a kettle. Suddenly she felt intense heat from the puff of steam gushing out of the spout of the kettle. She wondered whether the temperature of the steam was higher than that of the water boiling in the kettle. Comment.

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

Melting of wax is a physical change but burning of wax is a chemical change. Explain.

Show by an experiment that by increasing the temperature, the substance can be changed into liquid and then into vapours.

An element A forms an oxide A₂O₅.

1. What is the valency of element A?
2. What will be the formula of chloride of A?

What are (i) metals (ii) non-metals, and (iii) metalloids? Give two examples each of metals, non-metals and metalloids.

Is air a mixture or a compound? Give three reasons for your answer.