Caffeine contains 49.5% C, 28.8% N, 16.5% 0 and 5.20% H. Calculate the molecular formula. Given that 0.2 moles of caffeine weigh 38.04 g.

Caffeine contains 49.5% C, 28.8% N, 16.5% 0 and 5.20% H. Calculate the

1.	Caffeine contains 49.5% C, 28.8% N, 16.5% 0 and 5.20% H. Calculate the molecular formula. Given that 0.2 moles of caffeine weigh 38.04 g.
Answer» SOLUTION :Calculation of empirical formula of caffeine : The empirical formula of caffeine = `C_4N_2OH_5` Calculation of molecular formula : 0.2 moles of caffeine weigh = 38.84 G `therefore` 0.1 mole of caffeine will weigh `=38.84/0.2 XX 1 = 194.2` `therefore` Molecular mass of caffeine = 194.2 amu Empirical formula mass = `(12.01 xx 4) + (2 xx 14.01( + 16.0 + (5 xx 1.008) = 97.1` `therefore n =("Molecular mass")/("Empirical formula mass") = (194.2)/(971.1) = 2` Hence, the molecular formula of caffeine `= 2 xx C_(4)N_(2)OH_(5) = C_(8)N_(4)O_(2)H_(10)`.