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TYPES OF ERROR IN LABORATORY MEASUREMENTS
Learning Goal: To be able to identify specific types of error in the laboratory
Learning Goal: To be able to calculate percent error from measurements when given an accepted value
Error in the Lab
There is always a measure of error with measurements.
Types of Error
The primary types of error in experiments are:Operator Error (not acceptable – can easily
be fixed)Procedural or Design Error (procedure
needs to be modified)Instrumental Error (instrument not
calibrated)
Operator Error Due to a mistake that is the direct fault of the
scientist
(ex. Typing a number in wrongly on the calculator, not reading meniscus at eye level, copying the balance reading wrongly, not recording to the correct number of sig figs)
- Not acceptable in a lab report because they can be immediately fixed
Procedural or Design Error Error due to a faulty procedure or design
Examples: using a bunsen burner instead of a hot water bath caused the temperature to move upwards too quickly; not using a magnetic stirrer caused the solution not to completely dissolve
Instrument Error
Error due to a measuring instrument not being calibrated correctly.
Ex: a clock set 5 minutes fast, a balance that records 5 g less than the actual mass
Note: reading the instrument incorrectly or recording the wrong number of sig figs is an operator error, not an instrumental error
Which type of error?A thermometer records all temperatures 3 degrees too low.
Opera
tor e
rror
Proce
dural e
rr...
Instr
umental e
...
0% 0%0%
1. Operator error
2. Procedural error
3. Instrumental error
Which type of error?You record the length as 35.0cm but the correct resolution is 35.00cm.
Opera
tor e
rror
Proce
dural e
rr...
Instr
umental e
...
0% 0%0%
1. Operator error
2. Procedural error
3. Instrumental error
Which type of error?You should have heated the solution more to get all of the solute to dissolve.
Opera
tor e
rror
Proce
dural e
rr...
Instr
umental e
...
0% 0%0%
1. Operator error
2. Procedural error
3. Instrumental error
Percent Error
Percent Error – used to calculate how far your data is from the expected or theoretical value
