1. Measurement

2. Measurement A quantity that has both a number and a unit
Which is a measurement?
12 cm
134.54
0.0034

3. The Metric System Standard units of measurement (SI)
Temperature conversion:
Quantity
Unit
Symbol
Length
meter m
Mass
kilogram kg
Temperature
Kelvin K
Time
second s
Amount of substance
mole
mol
Converting temp; think about the alphabet
--C to K goes up in the alphabet, so add
--K to C goes down in the alphabet so subtract
°C = Kelvin

4. Metric Prefixes Prefix Meaning Factor Kilo (k) 103 Centi (c) 10−2
1000 times larger than the unit
103
Centi (c)
100 times smaller than the unit
10−2
Milli (m)
1000 times smaller than the unit
10−3
Micro (μ)
1 million times smaller than the unit
10−6
Nano (n)
1 billion times smaller than the unit
10−9

5. Scientific Notation Used to write really big and small numbers
6.02 ×1023
The coefficient is equal to or greater than 1 and less than 10
The exponent is a positive or negative integer
Circle and label coefficient

6. Writing Scientific Notation
For large numbers—
move the decimal to the left until one digit remains in front
Count the number of times the decimal moves
The exponent is positive
Example:
3,000  3 x103
405,000  4.05 x105
Underline large numbers, left, positive

7. For small numbers—
move the decimal to the right until one digit is in front
Count the number of times the decimal moves
The exponent is negative
Example:
 3.4 x10−4
 x10−7
Underline small numbers, right, negative

8. Accuracy
How close a measurement comes to the actual value of whatever is measured
The more # of significant digits, the more accurate the value

9. Precision
How close a series of measurements are to one another or “repeatability”
You must compare two or more measurements to each other

10. Accuracy vs Precision

11. Example: Jack has a height of 70 inches. Which sets of measurements are
Accurate and precise
Precise but not accurate
Neither precise nor accurate
69.5 in., 70.5 in., 70.1 in.
45.3 in., 62.1 in., 84.3 in
78.3 in., 78.0 in., 78.1 in

12. Percent Error
To find out how close you are to an accepted or actual value
Percent error =  exp val – act val  x 100%
act val
error
Point out the absolute value sign, we don’t care if we measured high or low

13. Example: Your data reads 99. 1g but the accepted value is 101
Example: Your data reads 99.1g but the accepted value is 101.0g, what is your percent error?
Percent error = 99.1g − 101.0g × 100
101.0g
%error = 1.88%
Point out the absolute value sign, we don’t care if we measured high or low

14. Measuring with Accuracy
Includes all the digits that are known, plus one that is estimated

15. Measuring with a Ruler 1. Measuring error = 1/10 of smallest division
ii.
Reading error is equal to 1/10 of the smallest division on the ruler
iii.

16. What is the following measurement?
Practice
What is the following measurement?

17. **Measure from the bottom of the meniscus
Measuring a Liquid
**Measure from the bottom of the meniscus

18. Practice
ii. i.

19. iv.
iii.

20. Still More measurements
not on the note takers

21. Sig Figs Show the Uncertainty in Measured Data
Review - Significant Figures
Sig Figs Show the Uncertainty in Measured Data
Measured data is written to convey 2 things!
the magnitude of the measurement
the extent of its reliability
Worker #1 reports a mass of 12 g
Worker #2 reports a mass of g
12 g means
12 ± 1 g
g means ± g
12 g has 2 sig figs
g has 6 sig fig
g is the more precise (certain, reliable) number
The more significant figures a measurement has, the more precise (certain) it is.

22. Making Measurements in the Lab: Correct Sig Figs in Recording Thermometer Data
A. The number of SFs in a measured value is equal to the number of known digits plus one uncertain digit.
23°C
23°C
22°C
22°C
21°C
21°C
you record 21.6°C
you record 21.68°C

23. Making Measurements in the Lab: Correct Sig Figs-Glassware with Graduations
0 mL
1 mL
2 mL
Example Y
A. If the glassware is marked every 10 mLs, the volume you record should be in mLs. (Example X)
B. If the glassware is marked every 1 mL, the volume you record should be in tenths of mLs.
C. If the glassware is marked every 0.1 mL, the volume you record should be in hundredths of mLs. (Example Y)
30 mL
10 mL
Example X
30-mL beaker:
the volume you record should be 13 mL
Buret marked in 0.1 mL you record volume as 0.67 mL

24. Making Measurements in the Lab: Recording Masses with Sig Figs
A. Record EVERY number (especially zeros) that appears on the display of the electronic balance.
B. Trailing zeros MUST be recorded.