Question

A compound containing only c, h, and o, was extracted from the bark of the sassafras tree. the combustion of 43.5 mg produced 118 mg of co2 and 24.2 mg of h2o. the molar mass of the compound was 162 g/mol. determine its empirical and molecular formulas.

Answer 1

% C = (12/44) x (118/43.5) x 100 = 74 %
% H = (2/18) x (24.2/43.5) x 100 = 6.18 %
% O = 100 - (74 + 6.2) = 19.82 %
Divide % of elements by atomic masses:
C = (74/12) = 6.17 ; H = (6.18/1) = 6.18 ; O = (19.82/16) = 1.24
Divide by the smallest (1.24)
C : H : O = 5 : 5 : 1
The empirical formula is C₅H₅O; it is mass = 81 g [(12 x 5) + (1 x 5) + (16 x 1)]
Molecular formula mass = 162
n = 162 / 81 = 2
Molecular formula (C₅H₅O)₂ = C₁₀H₁₀O₂