Using Scientific Measurements

FlashbackConvert 2.58 m to kilometers.

Accuracy and PrecisionAccuracy- the closeness of measurements to the correct value of the quantity measured

Precision- the closeness of a set of measurements

Accuracy- how close a measurement is to _____________.

Precision- how close a measurement is to ________________.

Measured values that are accurate are close to the accepted value. Measured values that are precise are close to one another , but they are not necessarily accurate.

Study CheckA technician measures the density of a substance in a lab. He records values of 2.000,1.999, and 2.001 g/mL. The correct value is 2.701. Were the technician’s results accurate? Were the results precise?

A student was asked to measure the pH of a solution. The student performed four trials. The table below shows the results obtained by the study:

If the actual pH of the solution was 6.40, comment on the student’s accuracy and precision.

Trial pH

1 4.51

2 4.50

3 4.52

4 4.50

Percentage ErrorThe accuracy of experimental results can be determined by calculating the percentage error.

Percentage error = Value experimental-Valueaccepted X 100 Valueaccepted

Study CheckWhat is the percentage error for a mass measurement of 17.7g if the correct value is 21.2g?

Study CheckA student took a calibrate 200.o g mass, weighed it on a laboratory balance, and found it read 196.5 g. What is the student’s percent error?

Error in MeasurementSome error or uncertainty always exists in any measurement. the skill of the measurer limits the reliability

of resultsthe conditions of measurement can affect the

outcome

Recording MeasurementsRecord the volume of liquid in the graduated cylinder to the correct number of digits.

A proper measurement should always go one more place value than the divisions marked on the instrument. For example, if the instrument is marked to every 0.1 unit, the measurement can be estimated to the hundredths place.

POGIL activity