Chemistry Reference
In-Depth Information
10. How close was your calculated value to the actual molar mass of
butane? What were some sources of error that could have caused
the results to be different from what was expected?
What's Going On?
The chemical formula for butane is C
4
H
10
and the actual molar mass of
butane is 58.12 g/mol. Figure 2 shows the structural formula of butane.
In this experiment, the butane was collected in a graduated cylinder
that was held under water to ensure that the gas was not lost to the
atmosphere. The volume was measured at the surface of the water to
ensure that the atmospheric pressure was equal to the combination of
gases within the graduated cylinder, which included butane and some
water vapor that was present due to evaporation. For this reason, Dalton's
law was used to calculate the pressure of butane. The pressure, volume,
and temperature can all be used to calculate the number of moles of
butane collected. Since the number of moles of a substance is equal to
its mass divided by its molar mass, the moles of butane and the mass
obtained from weighing the lighter before and after collection could be
used to determine the experimental molar mass of butane.
H
H
H
H
H
C
C
C
C
H
H
H
H
H
Figure 2
Structural formula for butane
Connections
The ideal gas equation was established as a combination of several
existing gas laws.
Boyle's law
(
P
1
V
1
=
P
2
V
2
) shows the relationship between
pressure and volume. Charles' law (
V
1
/
T
1
=
V
2
/
T
2
) shows the relationship
between volume and temperature. Avogadro's law (V
1
/
n
1
=
V
2
/
n
2
)
discusses the relationship between the volume of a gas and the number
of moles, and Gay-Lussac's law (
P
1
/
T
1
=
P
2
/
T
2
) shows the relationship
