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

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

Why is it advisable to use pressure cooker at higher altitudes for cooking food?

The chlorine atom is electrically neutral but chloride ion is charged. Explain.

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.

Draw a labeled diagram of the experimental set-up to study the latent heat of vaporization of water.

Compare the properties of electrons, protons and neutrons.

Non metals are usually poor conductors of heat and electricity. They are non-lustrous, non-sonorous, non-malleable and are coloured.

1. Name a lustrous non-metal.
2. Name a non-metal which exists as a liquid at room temperature.
3. The allotropic form of a non-metal is a good conductor of electricity. Name the allotrope.
4. Name a non-metal which is known to form the largest number of compounds.
5. Name a non-metal other than carbon which shows allotropy.
6. Name a non-metal which is required for combustion.

An element X has a mass number = 37 and it contains 17 protons.

1. Write the symbolic representation of the element.
2. Find the number of neutrons and electrons in the element.
3. Write the electronic configuration of the element.

Classify the following as physical or chemical changes:

1. Cooking of food.
2. Boiling of water.
3. Cutting of trees.
4. Dissolving salt in water.
5. Digestion of food.
6. Melting of ice.

Write a method to separate a mixture of sand and potash alum.