Matter in Our Surroundings — Science STD 9 — Question

Show by means of calculations that 5 moles of CO₂ and 5 moles of H₂O do not have the same mass. How much is the difference in their masses?

Explain the following giving examples.
Saturated solution.

In photosynthesis, 6 molecules of carbon dioxide combine with an equal number of water molecules through a complex series of reactions to give a molecule of glucose having a molecular formula C₆H₁₂O₆. How many grams of water would be required to produce 18g of glucose? Compute the volume of water so consumed assuming the density of water to be 1g cm^–3.

Name the scientist who studied the movement of pollen grains suspended in water through a microscope. What is this phenomenon known as?

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

Ice at 0°C is more effective in cooling than water at 0°C. Give reason.

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

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.

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.

Why burns caused by the steam are much more severe than boiling water?