Genchem1

1. UNCERTAINTY IN MEASUREMENT
ACCURACY,PRECISION AND ERROR

2. WHY DO ACCURACY AND PRECISION MATTER?
●Important in Science, Engineering and
everyday life.
●Helps improve reliability and quality of
measurements.
●Used in experiments, data collection,
and quality

3. WHAT IS ACCURACY?
●Indicates how close a measurement is to the
true or accepted value
Examples.
1. If the actual weight of an object is 100 g and
your scale reads 99.8 g, it’s accurate.

4. WHAT IS PRECISION?
●Precision is how close multiple measurements
are true to each other, regardless of the true
value.
●Refers to the closeness of measurements within
a set of data.
Example: If a scale gives 95.1 g, 95.2 g, 95.0 g
repeatedly, it is precise but not necessary
accurate.

5. A B C D
DARTS ANALOGY

6. A
LOW ACCURACY AND LOW PRECISION

7. LOW ACCURACY AND HIGH
PRECISION
B

8. HIGH ACCURACY AND LOW PRECISION
C

9. HIGH ACCURACY AND HIGH PRECISION
D

10. ERROR
Error – the difference between the accepted value and the
experimental value.
1. Formula

11. ERROR
Examples
1. In class you determine the melting point of salt is 755 deg C.
The actual value is 805 deg C. What is your percent error?

12. ERROR
2. Joshua uses his thermometer and finds the boiling point of ethyl
alcohol to be 75o C. He looks in a reference book and finds that the
actual boiling point of ethyl alcohol is 80oC. What is his percent error?