Matter in Our Surroundings — Science STD 9 — Question

A gold sample contains 90% of gold and the rest copper. How many atoms of gold are present in one gram of this sample of gold?

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

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?

How will you separate a mixture of sodium chloride and sand?

Define valency by taking examples of silicon and oxygen.

Copper sulphate reacts with sodium hydroxide to form a blue precipitate of copper hydroxide and sodium sulphate. In an experiment, 15.95g of copper sulphate reacted with 8.0g of sodium hydroxide to form 9.75g of copper hydroxide and 14.2g of sodium sulphate. Which law of chemical combination is illustrated by this data? Give reason for your choice.

How would you obtain sodium chloride from a mixture of sodium chloride and sulphur without using water?

In an experiment, 1.288g of barium sulphate was obtained from 1.03g of barium. In another experiment, 3.672g of barium sulphate gave, on reduction, 2.938g of barium. Show that these figures verify the law of constant proportions.

How will you separate iron pins from sand?