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D-4
If the flask was sealed, the pressure inside would increase. However, in this experiment the flask is not
sealed. The extra volume of the air-gas mixture escapes into the buret from the Erlenmeyer flask (pressure
remains constant). Hence, the volume of gas collected in the buret will be greater than that expected from
the amount of sulfamic acid used in the run. To estimate the error in the measured volume of nitrogen in
the buret, proceed as follows.
(a)
The volume available to the gas in the flask is V1 and the temperature of the flask at the start of
the reaction is T1. Use Charles' Law to calculate V2, the volume to which V1 expands at the
temperature at the end of the experiment, T2.
(b)
Subtract V1 from V2 to get
V, the excess volume.
(c)
Assume that
V goes into the buret. Calculate this excess volume as a percent of the final
volume of gas collected in the buret.
You will be asked to compare the experimentally determined value of R with the accepted literature value
of R. The percent error in your answer is defined as:
Percent error =
experimental value - accepted value
accepted value
x 100%
The experimentally determined value of R should be within ±10% of the literature value of R, if the
experiment is performed correctly.
