Class XI Chapter 1 – Some Basic Concepts of Chemistry

Class XI Chapter 1 – Some Basic Concepts of Chemistry   Calculate the molecular mass of the following: (i) H2O (ii) CO2 (iii) CH4 Answer H2O: The molecular mass of water, H2O = (2 × Atomic mass of hydrogen) + (1 × Atomic mass of oxygen) = [2(1.0084) + 1(16.00 u)] = 2.016 u + 16.00 u = 18.016 = 18.02 u CO2: The molecular mass of carbon dioxide, CO2 = (1 × Atomic mass of carbon) + (2 × Atomic mass of oxygen) = [1(12.011 u) + 2 (16.00 u)] = 12.011 u + 32.00 u = 44.01 u CH4: The molecular mass of methane, CH4 = (1 × Atomic mass of carbon) + (4 × Atomic mass of hydrogen) = [1(12.011 u) + 4 (1.008 u)] = 12.011 u + 4.032 u = 16.043 u    Calculate the mass percent of different elements present in sodium sulphate (Na2SO4). Answer The molecular formula of sodium sulphate is . Molar mass of = [(2 × 23.0) + (32.066) + 4 (16.00)] = 142.066 g ... Continues...