Task: Using an online simulation of combustion analysis, to calculate the empirical and molecular formulae of organic
substances.
Instructions:
Using the simulation of the elemental analysis of organic substances by combustion on
http://www.chm.davidson.edu/vce/Stoichiometry/CH.html complete the table below for at least 5 different
substance; A, B, C, D and an unknown. Make sure you read the instructions first!
Step 1
Step 2
Step 3
Step 4
Convert mass of CO2 produced to moles of C
present in the original sample.
Divide each
answer by the
smallest.
Write down
the empirical
formula.
Calculate the molecular
formula.
Convert mass of H2O produced to moles of H
present in the original sample:
Substance X
An experiment
showed that 0.438g
of an unknown
organic compound
combusted
completely to give
1.479g of CO2 and
0.303g of H2O. The
compound consisted
of the elements C,H
only. What is its
empirical formula? If
its molecular mass
is 78g mol-1 what is
its molecular
formula?
n(C) = mass CO2 x
1 mol CO2
Mr(CO2)
n(C) = 1.479 gCO2 x
x
0.0366/0.0366 = 1
1 mol C
1 mol CO2
x
44.01 gCO2
1 mol C
1 mol CO2
n(C) = 0.336059986366735 ≈ 0.0336 (4s.f.)
----------------------------------------------------------------------
n(H) = mass H2O x
1 mol H2O
Mr(H2O)
x
CnHn
-----------------------
1 mol H
x2
1 mol H2O
0.0366 /0.0366 = 1
n(H) = 0.303 gH2O x
Mr = 78 = (12.01n) + (1.01n)
78 = 13.02n
Thus n = 78 /13.02 = 5.99
n≈6
1 mol CO2
1 mol H2O
18.015gH2O
x
1 mol H
1 mol H2O
x2
n(H) = 0.0168193117235637 x2 ≈ 0.0336 (4 s.f.)
and the molecular formula is
therefore:
C6H6
Task: Using an online simulation of combustion analysis, to calculate the empirical and molecular formulae of organic
substances.
Substance A
An experiment
showed that
________ g of an
unknown organic
compound
combusted
completely to give
g of CO2 and g of
H2O. The compound
consisted of the
elements __, __, __,
__ only. What is its
empirical formula? If
its molecular mass
is ________g mol-1
what is its molecular
formula?
Substancet B
An experiment
showed that
________ g of an
unknown organic
compound
combusted
completely to give
g of CO2 and g of
H2O. The compound
consisted of the
elements __, __, __,
__ only. What is its
empirical formula? If
its molecular mass
is ________g mol-1
what is its molecular
formula?
Task: Using an online simulation of combustion analysis, to calculate the empirical and molecular formulae of organic
substances.
Substance C
An experiment
showed that
________ g of an
unknown organic
compound
combusted
completely to give
g of CO2 and g of
H2O. The compound
consisted of the
elements __, __, __,
__ only. What is its
empirical formula? If
its molecular mass
is ________g mol-1
what is its molecular
formula?
Substance D
An experiment
showed that
________ g of an
unknown organic
compound
combusted
completely to give
g of CO2 and g of
H2O. The compound
consisted of the
elements __, __, __,
__ only. What is its
empirical formula? If
its molecular mass
is ________g mol-1
what is its molecular
formula?