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Answer» (i) Molecular mass of H2O=2 × Atomic Mass of H+Atomic Mass of O=2+16=18 a.m.u (i) Molecular mass of CO2 =Atomic Mass of C+2 × Atomic Mass of O=12+32=44 a.m.u (i) Molecular mass of CH4 =Atomic Mass of C+4 × Atomic Mass of H=12+4=16 a.m.u (i) 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 (ii) 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 (iii) 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
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