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Atoms And Molecules
Describe some practical applications from daily life which make use of the concept of pressure.
Practical applications based on the concept of pressure are as given below:
1. A sharp knife cuts better than a blunt one. The area of a sharp edge is much less than the area of blunt edge. Therefore, the effective force per unit area is more for the sharp edge than the blunt edge. Hence, a sharp edge cuts better.
2. Railway tracks are laid on large sized wooden sleepers. Therefore, the force due to the weight of the train is on a larger area. Hence, this reduces the pressure considerably. This prevents sinking of the ground under the weight of the train.
3. Pins and nails are made to have pointed ends. Their pointed ends have very small area. When a force is applied over the head of a pin or a nail, it transmits a large pressure (force/area) on the surface and hence easily penetrates through the surface.
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What are polyatomic ions? Give examples.
(a) Magnesium chloride
(b) Calcium oxide
(c) Copper nitrate
(d) Aluminium chloride
(e) Calcium carbonate
Give the names of the elements in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Calculate the molar mass of the following substances:
(a) Ethylene
(b) Sulphur molecule, S8
(c) Phosphorus molecule, P4
(d) Hydrochloric acid, HCl
(e) Nitric acid, HNO3.
What is the mass of:
(a) 1 mole of nitrogen atoms
(b) 4 moles of aluminium atoms
(c) 10 moles of sodium sulphite.
Convert into mole
(a) 12 gm of oxygen gas
(b) 20 gm of water
(c) 22 gm of carbon dioxide.
What is the mass of?
(a) 0.2 mole oxygen atoms.
(b) 0.5 mole of water molecules.
Calculate the number of molecules of sulphur (S8) present in 16 gm of solid sulphur.
Calculate the number of aluminium ions present in 0.56 gm of aluminium oxide.
Explain law of conservation of mass.
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