1. I. Using Measurements (pp. 28 - 32)
CH. 2 - MEASUREMENT
I. Using Measurements
(pp )

2. A. Accuracy vs. Precision p. 10
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

3. Not Accurate Nor precise.
The average is close
to the center but the
individual values are
not similar

4. Precise, but not accurate
All measurements are close, but not at the “correct” value

5. Accurate AND Precise
All measurements are close, AND at the “correct” value

6. Identify each High Accuracy, high precision.
High accuracy, low precision
Low accuracy, high precision
Low accuracy, low precision

7. B. Percent Error p. 9 Indicates accuracy of a measurement your value
Have students calculate % Error using my measurements vs. their measurements.
accepted value

8. 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 %

9. C. Significant Figures p. 5
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

10. C. Significant Figures Counting Sig Figs (p. 4 of Unit 1 packet)
Count all numbers EXCEPT:
Leading zeros
Trailing zeros without a decimal point -- 2,500

11. Atlantic Pacific Rule Pacific Atlantic
If the decimal is ABSENT, start from the ATLANTIC side, go to the first non-zero digit and start counting.
If the decimal is PRESENT, start from the PACIFIC side, go to the first non-zero digit and start counting.

12. 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
2 sig figs

13. C. Significant Figures 3.75 mL + 4.1 mL 7.85 mL 3.75 mL + 4.1 mL
Calculating with Sig Figs
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
224 g
+ 130 g
354 g
 7.9 mL
 354 g

14. C. Significant Figures (13.91g/cm3)(23.3cm3) = 324.103g 324 g
Calculating with Sig Figs (con’t)
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

15. 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
Exact conversions: 1 m = 100 cm
“1” in any conversion: 1 in = 2.54 cm

16. 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

17. D. Scientific Notation p. 3
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.

18. 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

19. D. Scientific Notation Calculating with 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