An organic acid has the following composition by mass, Empirical formula, organic compound, Empirical formula, Molecular formula
PROBLEM:
An organic
acid has the following composition by mass,
Carbon = 40.0%, Hyfrogen = 6.7% and Oxygen = 53.3%
Its mass
spectrum shows the major peaks,
including the molecular ion at m/e
values 15, 43, 45 and 60. Calculate the
empirical and molecular formula of the compound by using the above values also suggests structural
formula to this acid. After finding the molecular formula also identify various
specious responsibilities for the peaks in mass spectrum.
ANSWER:
Empirical
formula = CH2O
Molecular
formula= C2H4O2 or CH3COOH
CH3+
= 15 m/e, CH3CO+=43 m/e, CO2H+ = 45 m/e and CH3CO2H+=
60 m/e
PROBLEM:
In an experiment, 0.240g of magnesium ribbon
produced 0.400g of magnesium oxide. Calculate its empirical formula.
ANSWER:
MgO
PROBLEM:
An oxide of copper has the following
composition by mass;
Cu = 0.635g & O = 0.080g
Calculate the empirical formula of
the oxide.
ANSWER:
Cu2O
PROBLEM:
0.500g of an organic compound “X” containing only carbon, hydrogen and
oxygen produces 0.733g of CO2 and 0.300g of H2O on
complete combustion. The mass spectrum of the compound shows it has a molecular
mass of 60. Calculate its molecular & empirical formula.
ANSWER:
Empirical formula = CH2O
Molecular formula = C2H4O2
PROBLEM:
On complete combustion of 0.400g of a
hydrocarbon, 1.257g of CO2 and 0.514 of water were produced. Calculate the
empirical formula of the hydrocarbon. If the relative molecular mass of the
hydrocarbon is 84 then, what is its molecular formula?
ANSWER:
Empirical formula = CH2
Molecular formula = C6H12
PROBLEM:
A compound of nickel wa analysed and shown to have the following
%age composition by mass;
Ni = 37.9% ; S=20.7% ; O = 41.4%
Calculate its empirical formula.
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