Topic 11 - Measurement and Data Processing
11.1 Uncertainties and errors in measurement and results
Four groups have done a calorimetric experiment to
determine the enthalpy change of a reaction in aqueous
solution, for which the literature value is 38.73 kJ mol-1.
The values found by the groups (in kJ mol-1) were:
A 35.1 ± 0.3
C 33.2 ± 0.1
B 36.5 ± 0.5
D 34.7 ± 0.2
1.
Which result is the most precise?
2.
Which result is the most accurate?
3.
Do you think the major problem is
A
B
C
D
4.
C
D
Using a more precise thermometer.
Not assuming that the specific heat of
the solution equalled that of water.
Using pipettes rather than measuring
cylinders.
Improving the insulation of the
calorimeter.
Which of the following is the best way to report the
mean result of the group?
A
B
C
D
6.
Which result has the lowest absolute uncertainty?
A
B
C
D
8.
A
B
C
D
9.
34.875 ± 0.100 kJ mol-1.
34.9 ± 0.5 kJ mol-1.
34.9 ± 0.8 kJ mol-1.
35 ± 2 kJ mol-1.
Repeating an experiment a number of times will lead
to a decrease in:
A
B
C
D
the random error.
the systematic error.
both the random and the systematic error.
neither the random and the systematic error.
34.875 ± 0.017
749 ± 5
0.0004 ± 0.0001
87500 ± 200
Which result has the lowest percentage uncertainty?
34.875 ± 0.017
749 ± 5
0.0004 ± 0.0001
87500 ± 200
If x = 749 ± 5 and y = 34.8 ± 0.7, which one of
the following will have the greatest percentage
uncertainty?
A
B
C
D
If you were to repeat the experiment which of the
following is most likely to be the improvement that
would most improve the result?
A
B
5.
Random error
Systematic error
Both are equally important
It is not possible to tell from the data given
7.
x+y
x-y
x/y
x.√y
10. Give the result and the absolute uncertainty, to the correct
precision, of the following calculations:
a)
20.1 ± 0.1 + 2.75 ± 0.05
b)
115.4 ± 0.2 × 8.137 ± 0.001
c)
0.572 ± 0.001 (17.6 0.2 - 114 ± 1)
d)
(1 - 0.276 ± 0.002)/0.024 ± 0.001
e)
52800 ± 100/ √(17.2 ± 0.2 - 2.37 ± 0.01)