(a) A researcher analyzed an unknown solid, extracted from the bark of spruce tr
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Question
(a) A researcher analyzed an unknown solid, extracted from the bark of spruce trees, to determine its percentage composition. An 11.32 mg sample was burned in a combustion apparatus. The carbon dioxide (24.87 mg) and water (5.82 mg) were collected and weighed. From the results of this analysis, calculate the percentage composition of the unknown solid.
(b) Determine the empirical formula of the unknown solid.
(c) Through mass spectrum, the molecular mass was found to be 420 g/mole. What is the molecular formula?
(d) How many aromatic rings could this compound contain?
Explanation / Answer
a]
1 mole of CO2 contains 1 mole of C and 2 moles of O
Moles of CO2 = 24.87 mg / 44 = 5.65*10^-4
Moles of C = 5.65*10^-4
1 mole of H2O contains 2 moles of H and 1 mole of O
Moles of H2O = 5.82mg /18 = 3.23*10^-4
Moles of H = 6.46*10^-4
Mass of C = 5.65*10^-4 *12 = 6.78 mg
Mass of H = 6.46*10^-4 *1 = 0.646 mg
TOtal = 11.32 mg
Mass of O = 11.32 - 6.78-0.646 = 3.894 mg
Moles of O = 2.433*10^-4
b]
Mole ratio
C :O :H = 7 : 3 : 8
C7H8O3 = 140 gms
c]
Molecular fomula is 3*Empirical formula
C21H24O9
d]
Probably 3 aromatic rings
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