Types of Error in Laboratory Measurements

1. 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 Types of Error in Laboratory Measurements

2. Error in the Lab There is always a measure of error with measurements.

3. 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)

4. 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

5. 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

6. 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

7. Which type of error?A thermometer records all temperatures 3 degrees too low. • Operator error • Procedural error • Instrumental error

8. Which type of error?You record the length as 35.0cm but the correct resolution is 35.00cm. • Operator error • Procedural error • Instrumental error

9. Which type of error?You should have heated the solution more to get all of the solute to dissolve. • Operator error • Procedural error • Instrumental error

10. Percent Error • Percent Error – used to calculate how far your data is from the expected or theoretical value