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. Operator error Procedural error Instrumental error

Which type of error. You record the length as 35 Which type of error? You record the length as 35.0cm but the correct resolution is 35.00cm. Operator error Procedural error Instrumental error

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

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