1. 2.3 Using Scientific Measurements

2. Accuracy vs. Precision
Accuracy- closeness of measurement to correct or accepted value
Precision- closeness of a set of measurements

3. Accuracy vs. Precision ACCURATE = CORRECT PRECISE = CONSISTENT
Accuracy - how close a measurement is to the accepted value
Precision - how close a series of measurements are to each other
ACCURATE = CORRECT
PRECISE = CONSISTENT

4. Accuracy vs. Precision

5. Percent Error your value accepted value
Indicates accuracy of a measurement
your value
accepted value

6. Percent Error % error = 2.9 %
A student determines the density of a substance to be 1.40 g/mL. Find the % error if the accepted value of the density is 1.36 g/mL.
% error = 2.9 %

7. Percent Error
A technician experimentally determined the boiling point of octane to be 124.1ºC. The actual boiling point of octane is 125.7ºC. Calculate the error and percent error.
Error= 1.6ºC
Percent error= %

8. Significant Figures Indicates precision of a measurement.
Recording Sig Figs
Sig figs in a measurement include the known digits plus a final estimated digit
2.31 cm

9. Significant Figures
All certain digits plus one estimated digit

10. The underlined zeros do not count.
Significant Figures
Counting Sig Figs
All non-zero numbers are sig figs
Zeros depend on location in number:
LEADING zeros never count
EMBEDDED zeros always count ,005
TRAILING zeros only count if
there is a decimal point , ,500.
The underlined zeros do not count.

11. Practice 101.02 EMBEDDED 5 20.0 TRAILING w/ 3 0.005302 LEADING 4
TRAILING w/o 2
TRAILING w/ 4

12. Rounding Need to use rounding to write a calculation correctly
Calculator gives you lots of insignificant figures and you must round to the right place
When rounding, look at the digit after the one you can keep
Greater than or equal to 5, round up
Less than 5, keep the same

13. Examples Make the following have 3 sig figs: 761.50  762
 762
 14.3
 10.4
 10800
 8020
 204

14. Using Sig Figs in Calculations
Adding/Subtracting:
end with the least number of decimal places

15. Using Sig Figs in Calculations
Adding/Subtracting:
end with the least number of decimal places

16. Using Sig Figs in Calculations
Multiplying/Dividing:
end with the least number of sig figs

17. Using Sig Figs in Calculations
Multiplying/Dividing:
end with the least number of sig figs