Key Formula
1 mole of atoms = 6. 022 × 1023 atoms = Gram atomic mass or Molar mass of element
Number of moles = Mass of element / Molar Mass
Number of moles = Given number of atoms / Avogadro number
or m = n × M and N = n × N0
Let us apply these formula to solve numerical problems.
Q. In a reaction 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide. 0.9 g water and 8.2 g of sodium ethanoate. Show that these observations are in agreement with the law of conservation of mass.
[NCERT]
Sodium carbonate + ethanoic acid sodium ethanoate + carbon dioxide + water.
Q. Hydrogen and oxygen combine in the ratio of 1 : 8 by mass to form water. What mass of oxygen gas would be required to react completely with 3 g of hydrogen gas?
[NCERT]
Q. Which postulate of Dalton's atomic theory is the result of the law of conservation of mass?
[NCERT]
(b) Law of constant Proportions / Law of definite proportions :
Q. Which postulate of Dalton's atomic theory can explain the law of definite proportions?
[NCERT]
Q. Define the atomic mass unit.
[NCERT]
Q. Why is it not possible to see an atom with naked eyes?
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Q. Calculate the molecular masses of H2, O2, Cl2, CO2, CH4, C2H6, C2H4, NH3, CH3OH.
[NCERT]
Q. Calculate the formula unit masses of ZnO, Na2O, K2CO3, given atomic masses of Zn = 65 u, Na = 23 u,
K = 39 u, C = 12 u and O = 16 u
[NCERT]
Q. Calculate the molar mass of the following substances.
[NCERT]
Q. What is meant by the term chemical formula?
[NCERT]
Q. How many atoms are present in a
(i) H2S molecule and
(ii) ?
[NCERT]
Q. What are polyatomic ions? Give examples
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Q. Give the names of the elements present in the following compounds.
[NCERT]
Q. Write down the formulae of
[NCERT]
Q. Write down the names of compounds represented by the following formulae :
[NCERT]
Q. Write the chemical formulae of the following.
[NCERT]
Q. If one mole of carbon atoms weighs 12 grams, what is the mass (in grams) of 1 atom of carbon?
[NCERT]
Q. Which has more number of atoms, 100 grams of sodium or 100 grams of iron (given, atomic mass of
Na = 23u, Fe = 56u)?
[NCERT]
Q. A 0.24 g sample of compound of oxygen and boron was found by analysis to contain 0.096 g of boron and 0.144 g of oxygen. Calculate the percentage composition of the compound by weight.
[NCERT]
Q. When 3.0 g of carbon is burnt in 8.00 g oxygen, 11.00 g of carbon dioxide is produced. What mass of carbon dioxide will be formed when 3.0 g of carbon is burnt in 50.00 g of oxygen? Which law of chemical combination will govern your answer?
[NCERT]
Q. What is the mass of –
(a) 1 mole of nitrogen atoms?
(b) 4 moles of aluminium atoms (Atomic mass of aluminium = 27)?
(c) 10 moles of sodium sulphite (Na2SO3)?
[NCERT]
Q. Convert into mole.
(a) 12 g of oxygen gas
(b) 20 g of water
(c) 22 g of carbon dioxide
[NCERT]
Q. What is the mass of :
(a) 0.2 mole of oxygen atoms?
(b) 0.5 mole of water molecules?
[NCERT]
1. What is an atom? |
2. What is a molecule? |
3. How are atoms and molecules related? |
4. What are the differences between atoms and molecules? |
5. Can atoms exist independently without forming molecules? |
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