1. Scientific Measurements

2. Measurements Objective Distinguish between accuracy and precision
Determine the number of significant figures in measurements
Perform mathematical operations involving significant
Convert measurements into scientific notation
Distinguish between inversely and directly proportional relationships

3. Measurements Accuracy and Precision
Accuracy refers to the closeness of measurements to the correct or accepted value of the quantity measured
Precision refers to the closeness of a set of measurements of the same quantity made in the same way

4. Measurements
Accuracy and Precision

5. Measurements Accuracy and Precision
Percentage error is calculated by subtracting the accepted value from the experimental value, dividing the difference by the accepted value, and then multiplying by 100

6. Measurements Accuracy and Precision Sample Problem
A student measures the mass and volume of a substance and calculates its density as 1.40 g/mL. The correct, or accepted, value of the density is 1.30 g/mL. What is the percentage error of the student’s measurement?

7. Measurements
Accuracy and Precision
Sample Problem Solution

8. Measurements Accuracy and Precision Error in measurement
Skill of the measurer
Conditions of measurement
Measuring instruments

9. Measurements Significant Figures
Significant figures in a measurement consist of all the digits known with certainty plus one final digit, which is somewhat uncertain or is estimated
The term significant does not mean certain

10. Measurements Significant Figures Reporting measurements
using significant figures

11. Measurements Significant Figures
Determining the number of significant figures

12. Measurements
Significant Figures

13. Measurements Significant Figures Sample Problem
How many significant figures are in each of the following measurements?
a g
b cm
c. 910 m
d L
e kg

14. Measurements Significant Figures Sample Problem Solution a. 28.6 g
There are no zeros, so all three digits are significant
b cm
By rule 4, the zero is significant because it is immediately followed by a decimal point; there are 4 significant figures
c. 910 m
By rule 4, the zero is not significant; there are 2 significant figures

15. Measurements Significant Figures Sample Problem Solution d. 0.04604 L
By rule 2, the first two zeros are not significant; by rule 1, the third zero is significant; there are 4 significant figures
e kg
By rule 2, the first three zeros are not significant; by rule 3, the last three zeros are significant; there are 5 significant figures

16. Measurements
Significant Figures

17. Measurements
Significant Figures

18. Measurements Significant Figures
Addition or subtraction with significant figures
When adding or subtracting decimals, the answer must have the same number of digits to the right of the decimal point as there are in the measurement having the fewest digits to the right of the decimal point

19. Measurements Significant Figures
Multiplication or division with significant figures
For multiplication or division, the answer can have no more significant figures than are in the measurement with the fewest number of significant figures

20. Measurements Significant Figures Sample Problems
Express each answer to the correct number of significant figures
a m m
b. 2.4 g/mL  mL

21. Measurements Significant Figures Sample Problem Solutions
a m m = 2.84 m
There should be two digits to the right of the decimal point, to
match 5.44 m
b. 2.4 g/mL  mL = 38 g
There should be two significant figures in the answer, to match
2.4 g/mL

22. Measurements Scientific Notation
In scientific notation, numbers are written in the form M × 10n, where the factor M is a number greater than or equal to 1 but less than 10 and n is a whole number
Example: mm = 1.2 × 10−4 mm
Move the decimal point four places to the right and multiply the number by 10−4

23. Measurements Scientific Notation
Determine M by moving the decimal point in the original number to the left or the right so that only one nonzero digit remains to the left of the decimal point
Determine n by counting the number of places that you moved the decimal point. If you moved it to the left, n is positive. If you moved it to the right, n is negative

24. Measurements Scientific Notation
Addition and subtraction —These operations can be performed only if the values have the same exponent (n factor)
Example: 4.2 × 104 kg × 103 kg or

25. Measurements Scientific Notation
Multiplication —The M factors are multiplied, and the exponents are added algebraically
Example: (5.23 × 106 µm)(7.1 × 10−2 µm)
= (5.23 × 7.1)( )
= × 104 µm2
= 3.7  105 µm2

26. Measurements Scientific Notation
Division — The M factors are divided, and the exponent of the denominator is subtracted from that of the numerator
Example:
= (5.44 / 8.1)( )
= × 103
= 6.7  102 g/mol

27. Measurements Direct Proportion
Two quantities are directly proportional to each other if dividing one by the other gives a constant value
read as “y is proportional to x.”

28. Measurements
Direct Proportion

29. Measurements Inverse Proportion
Two quantities are inversely proportional to each other if their product is constant
read as “y is proportional to 1 divided by x.”

30. Measurements
Inverse Proportion