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# 131 1-31-2011

## on Feb 01, 2011

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significant figures

significant figures

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## 131 1-31-2011Presentation Transcript

• review
35 mm = _______ dm _____ mm _____ km
0.25 dm3 = _____ cL = ______ cc
Bromine heptafluoride _____
N2 S3 ________________________
Na2S
6500000 = ________
0.00344 = __________
3.6 X 10-3 x 6.1 X 10-6 = _____________
3.6 X 10-3 / 6.1 X 10-6 = _____________
• review
35 mm = 0.35 dm = 35000mm = 0.000035km
0.25 dm3 (L) = 25cL = 250 cc (mL)
Bromine heptafluoride__BrF7___
N2 S3 dinitrogentrisulfide
Na2S sodium sulfide
6500000 = 6.5 X 106
0.00344 = 3.44 X 10-3
3.6 X 10-3 x 6.1 X 10-6 = 21.96 X 10-9 = 2.2 X 10-8
3.6 X 10-3 / 6.1 X 10-6 = 0.59 X 103 = 5.9 X 102
• Measurements are estimates
Exact numbers
Counted -- I have 3 sons
Defined -- 4 qt in 1 gal
Measured
“exactness” limited by measuring device, object and user
• Significant figures
Measured and exact number
Exact:
Counted
13,000 people attended the conference
49 citizens attended the council meeting
Defined
12 in = 1 ft, 2.54 cm = 1 in
1 kg = 2.2 lb NOT defined – remember weight changes!!!
Measurements
All are estimates – depend on precision of device
• 16 oz = 1 lb, exact -- defined
2.54 cm = 1 in, exaact -- defined
454 g = 1 lb, measured
1.6 km = 1 mi not exact (rounded off for convenience)
Actual exact number:
1 mi X 5280ft/mi X 12 in/ft X 2.54 cm/in = 160934 cm
or 1.609344 km this would be the EXACT conversion
Exact or measured??
Measuring
Estimate an
If possible
If lines are very
Close together
May not be
Practical!!!
A real meter stick, you probably cannot
This means you think the real
Value is between 2.9 and 3.1
Not between 2 and 4!!
• Counting Significant Figures
Number of Significant Figures
38.15 cm
5.6 ft
65.6 lb
122.55 m
Complete: All non-zero digits in a measured number are (significant or not significant).
Number of Significant Figures
0.008 mm
0.0156 oz
0.0042 lb
0.000262 mL
Complete: Leading zeros in decimal numbers are (significant or not significant).
• Sandwiched Zeros
Number of Significant Figures
50.8 mm
2001 min
0.702 lb
0.00405 m
Complete: Zeros between nonzero numbers are (significant or not significant).
• Trailing Zeros
Number of Significant Figures
25,000 in.
200 yr
48,600 gal
25,005,000 g
Complete: Trailing zeros in numbers without decimals are (significant or not significant) if they are serving as place holders.
• review
35 mm = _______ dm _____ mm _____ km
0.25 dm3 = _____ cL = ______ cc
Bromine heptafluoride _____
N2 S3 ________________________
Na2S
6500000 = ________
0.00344 = __________
3.6 X 10-3 x 6.1 X 10-6 = _____________
3.6 X 10-3 / 6.1 X 10-6 = _____________
• review
35 mm = 0.35 dm = 35000mm = 0.000035km
0.25 dm3 (L) = 25cL = 250 cc (mL)
Bromine heptafluoride__BrF7___
N2 S3 dinitrogentrisulfide
Na2S sodium sulfide
6500000 = 6.5 X 106
0.00344 = 3.44 X 10-3
3.6 X 10-3 x 6.1 X 10-6 = 21.96 X 10-9 = 2.2 X 10-8
3.6 X 10-3 / 6.1 X 10-6 = 0.59 X 103 = 5.9 X 102
• Measurements are estimates
Exact numbers
Counted -- I have 3 sons
Defined -- 4 qt in 1 gal
Measured
“exactness” limited by measuring device, object and user
• Significant figures
Measured and exact number
Exact:
Counted
13,000 people attended the conference
49 citizens attended the council meeting
Defined
12 in = 1 ft, 2.54 cm = 1 in
1 kg = 2.2 lb NOT defined – remember weight changes!!!
Measurements
All are estimates – depend on precision of device
• 16 oz = 1 lb, exact -- defined
2.54 cm = 1 in, exaact -- defined
454 g = 1 lb, measured
1.6 km = 1 mi not exact (rounded off for convenience)
Actual exact number:
1 mi X 5280ft/mi X 12 in/ft X 2.54 cm/in = 160934 cm
or 1.609344 km this would be the EXACT conversion
Exact or measured??
Measuring
Estimate an
If possible
If lines are very
Close together
May not be
Practical!!!
A real meter stick, you probably cannot
This means you think the real
Value is between 2.9 and 3.1
Not between 2 and 4!!
• Counting Significant Figures
Number of Significant Figures
38.15 cm
5.6 ft
65.6 lb
122.55 m
Complete: All non-zero digits in a measured number are (significant or not significant).
Number of Significant Figures
0.008 mm
0.0156 oz
0.0042 lb
0.000262 mL
Complete: Leading zeros in decimal numbers are (significant or not significant).
• Sandwiched Zeros
Number of Significant Figures
50.8 mm
2001 min
0.702 lb
0.00405 m
Complete: Zeros between nonzero numbers are (significant or not significant).
• Trailing Zeros
Number of Significant Figures
25,000 in.
200 yr
48,600 gal
25,005,000 g
Complete: Trailing zeros in numbers without decimals are (significant or not significant) if they are serving as place holders.
• HW
Quiz Wed: metrics, sci not, naming
HW problems: CH 1: 9-16-24, 61, 62
53 a,c (c volume displacement), 54 (density)
Next class: classification of matter, chem and physical properties, (Ch3 sec 1 and Ch 5 sec 3) start conversion factors (Ch 1: sec 6,7,8)
Check out mastering chemistry for problems!!
• Learning Check
A. Which answers contain 3 significant figures?
0.4760 2) 0.00476 3) 4760
B. All the zeros are significant in
1) 0.00307 2) 25.300 3) 2.050 x 103
C. 534,675 rounded to 3 significant figures is
1) 535 2) 535,000 3) 5.35 x 105
Answers: a: 2/3; b: 2/3; c: 2/3
• Learning Check
In which set(s) do both numbers contain the same number of significant figures?
1) 22.0 and 22.00
2) 400.0 and 40
3) 0.000015 and 150,000
• Learning Check
State the number of significant figures in each of the following:
A. 0.030 m1 2 3
B. 4.050 L 2 3 4
C. 0.0008 g 1 2 4
D. 3.00 m 1 2 3
E. 2,080,000 bees 3 5 7
29 people attended the conference ???EXACT
Answers: a 2 b 4 c 1 d 3 e 3
• Significant Numbers in Calculations
• A calculated answer cannot be more precise than the measuring tool.
• A calculated answer must match the least precise measurement.
• Significant figures are needed for final answers from
2) multiplying or dividing
The answer has the same number of decimal places as the measurement with the fewest decimal places.
25.2 gone decimal place
+ 1.34 gtwo decimal places
26.54 answer 26.5 one decimal place
• Learning Check
In each calculation, round the answer to the correct number of significant figures.
A. 235.05 + 19.6 + 2.1 =
1) 256.75 2) 256.8 3) 257
B. 58.925 - 18.2 =
1) 40.725 2) 40.73 3) 40.7