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Atoms And Molecules
(i) Define centre of gravity of a body.
(ii) What is the difference between centre of gravity and centre of mass?
(i) Centre of gravity: The point at which the resultant of all the parallel forces due to gravity experienced by various particles of the body acts or at which the whole weight of the body acts is called the centre of gravity.
If a force equal to the weight of the body is applied at this point vertically upwards, the body will remain in equilibrium.
Hence a body can be supported at its centre of gravity.
Fig. (i): Centre of Gravity of Some Regular Bodies
Fig. | Body | Centre of gravity |
(a) (b) (c) (d) (e) (f) | Right cylinder Circular disc Triangular lamina A solid cone Rectangular lamina Circular ring | Mid. point Centre of the disc The point of intersection of medians. Point on the axis at a distance h/4 from the base of the cone, h being its height. Point of intersection of diagonals Centre of the ring (outside the body) |
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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.
50 g of 10% lead nitrate is mixed with 50 g of 10% sodium chloride in a closed vessel. After the reaction has taken place, it was found that 6.83 g of lead chloride was precipitated. Besides, the reaction mixture contained 90 g water and sodium nitrate. Calculate the amount of sodium nitrate formed.
Name and explain two important laws of chemical combination ?
What are the postulates of Dalton’s atomic theory of matter?
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