Page 2 - 3. LESSON NOTES-(NUMERICALS BASED ON MOLE CONCEPT)
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Examples: Conversion into number of moles

               Q.1 Convert the following into moles
                               23
               a) 12.044 X 10  atoms of sulphur
               b) 71 g of chlorine gas
               Ans: a) n=N/NA
                                    23
                                                 23
               Or, n= 12.044 X 10 /6.022 X10  = 2 moles
               b) Molar mass of Chlorine gas ( Cl2) = 35.5 X2 =71 g
               n= m/M=71/71= 1 mole
               Conversion into mass:
               Q.2 Calculate the mass of the following
               a)  2 moles of calcium atoms
               b) 7 moles of CaCO3 molecules
               Ans: a) molar mass of Ca= 40g
               m= n X M = 2X 40=80g
               b) Molar mass of CaCO3 = 100g
               m= n X M= 100 X 7 = 700 g
               Conversions of Number of particles into mass:
               Q3.a) Calculate the mass of 30.11 X 10  molecules of Carbon dioxide
                                                         23
                                                      22
               b) Calculate the mass of 6.022 X 10 atoms of sodium.
                                                23
                                                             23
               Ans: a) n= N/NA = 30. 11 X 10 /6.022 X10  = 5 moles
               Molar mass of Carbon dioxide= 44 g
               m=n X M= 5 X44= 220g
               b) n= N/NA = 6.022 X 10 /6.022 X10  = 1/10 moles= 0.1 moles
                                                      23
                                         22
               Molar mass of Sodium = 23 g
               m=n X M= 0.1 X 23= 2.3 g










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