1. III. Using Measurements (p. 44 - 57)
CH. 2 - MEASUREMENT
III. Using Measurements
(p )
C. Johannesson

2. A. Accuracy vs. Precision
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
C. Johannesson

3. B. Percent Error Indicates accuracy of a measurement your value
accepted value
C. Johannesson

4. B. 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 %
C. Johannesson

5. C. Significant Figures Indicate precision of a measurement.
Recording Sig Figs
Sig figs in a measurement include the known digits plus a final estimated digit
2.35 cm
C. Johannesson

6. C. Significant Figures Counting Sig Figs (Table 2-5, p.47)
Count all numbers EXCEPT:
Leading zeros
Trailing zeros without a decimal point -- 2,500
C. Johannesson

7. Counting Sig Fig Examples
C. Significant Figures
Counting Sig Fig Examples
4 sig figs
3 sig figs
3. 5,280
3. 5,280
3 sig figs
Write on board:
sig figs
sig fig
sig fig
sig figs
sig figs
sig fig
sigs figs
2 sig figs
C. Johannesson

8. C. Significant Figures (13.91g/cm3)(23.3cm3) = 324.103g 324 g
Calculating with Sig Figs
Multiply/Divide - The # with the fewest sig figs determines the # of sig figs in the answer.
(13.91g/cm3)(23.3cm3) = g
4 SF
3 SF
3 SF
324 g
C. Johannesson

9. C. Significant Figures 3.75 mL + 4.1 mL 7.85 mL 3.75 mL + 4.1 mL
Calculating with Sig Figs (con’t)
Add/Subtract - The # with the lowest decimal value determines the place of the last sig fig in the answer.
3.75 mL mL
7.85 mL
3.75 mL mL
7.85 mL
 7.9 mL
C. Johannesson

10. C. Significant Figures Calculating with Sig Figs (con’t)
Exact Numbers do not limit the # of sig figs in the answer.
Counting numbers: 12 students, 4 soccer balls, 7cups, etc.
Exact conversions: 1 m = 100 cm, 1 foot = 12 in, 1 day = 24 hours, etc.
C. Johannesson

11. C. Significant Figures Practice Problems 5. (15.30 g) ÷ (6.4 mL)
4 SF
2 SF
= g/mL
 2.4 g/mL
2 SF g g
 18.1 g
18.06 g
C. Johannesson

12. D. Scientific Notation 65,000 kg  6.5 × 104 kg
Converting into Sci. Notation:
Move decimal until there’s 1 digit to its left. Places moved = exponent.
Large # (>1)  positive exponent
Small # (<1)  negative exponent
Only include sig figs.
C. Johannesson

13. D. Scientific Notation Practice Problems 7. 2,400,000 g 8. 0.00256 kg
9. 7  10-5 km
 104 mm
2.4  106 g
2.56  10-3 kg km
62,000 mm
C. Johannesson

14. D. Scientific Notation (5.44 × 107 g) ÷ (8.1 × 104 mol) =
Dividing in Sci. Notation
(5.44 × 107 g) ÷ (8.1 × 104 mol) =
Type on your calculator:
EXP EE
EXP EE
ENTER
EXE
5.44 7
8.1 ÷ 4 =
= 670 g/mol
= 6.7 × 102 g/mol
C. Johannesson

15. D. Scientific Notation

16. D. Scientific Notation Multiplying in Sci. Notation
(5.23 × 106 m) (7.1 × 10-2 m) =
Type on your calculator:
EXP EE
EXP EE
ENTER
EXE
5.23 6
7.1 x -2

17. D. Scientific Notation
C. Johannesson

18. D. Scientific Notation Adding & Subtracting in Sci. Notation
(4.2 × 104 kg) + (0.79 × 104 m) =
Type on your calculator:
EXP EE
EXP EE
ENTER
EXE
4.2 4
0.79 + 4
= × 104 kg

19. D. Scientific Notation
Adding & Subtracting Sci. Notation without a Calc.
Exponents MUST have the same value!
If not, decimal point must be moved (either right or left) to make exponents equal
Add or subtract the first factors
Exponents remain the same, or may need to be adjusted if the answer has more than 1 digit to the left of the decimal point.
C. Johannesson

20. D. Scientific Notation

21. E. Proportions Direct Proportion Inverse Proportion y x y x
C. Johannesson