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Atoms And Molecules
Comment on the statement. “A molecule is the smallest particle of a substance (element or compound) which has the properties of the substance and is stable.”
It is true that a molecule is the smallest particle of a substance which has the properties of that substance and is stable. In case of gases as example oxygen, a molecule (O2) is stable and gives properties of oxygen gas, whereas atom ‘O’ is not stable and does not represent oxygen gas. In case of noble gases such as helium, a molecule is of monoatomic helium atom (He) and represents helium gas and is also stable. In case of a compound, e.g., carbon dioxide, properties of carbon dioxide molecule are the properties of carbon dioxide gas. A molecule of carbon dioxide is stable.
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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.
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 ?
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