1. Unit 2 Measurement Metrics Scientific Notation Uncertainty
Chemistry Notes
Unit 2 Measurement
Metrics
Scientific Notation
Uncertainty

2. Metric Measurement
Fundamental – deals with single measurements that describes a single phenomenon
Ex: time, distance, mass
Derived – deals with two or more measurements that describe a single phenomenon
Ex: m/s, Kg*m/s2, m/s2, N*m

3. SOME REVIEW FOR YOU
The metric system is much easier than our standard system of measurement because units with in the metric system are powers of ten.
Ex: convert 1200 g to kg
Answer  1.20 kg (just move the decimal)
Ex: convert 40 oz.  lbs
Answer  2 ½ lbs (have to do some math)

4. SOME REVIEW FOR YOU Metric Measurement
Some basic units  see table 2.1 on page 29
Length  meters
Time  seconds
Mass  kilogram
Metric Prefixes  see table 2.2 on page 29
Micro m
Mill m
Centi m
Deci m
Kilo m

5. SOME REVIEW FOR YOU Converting between metric units Remember
SSL (Smaller units to larger units move decimal to the left)
K,H,D,b,d,c,m
E.g. When you convert from milli- to deci- you move the decimal point two places

6. SOME REVIEW FOR YOU Conversion with Unit Analysis Method:
Used to convert standard to metric
Standard form below:
## given units ## desired units = desired units
## given units
If set up correctly, the given units will cancel out. That how you know you set it up right.

7. SOME REVIEW FOR YOU Mass = the amount of matter in an object
Measured in kilograms (kg)
Not to be confused weight. Weight is more comparable to force,
W = mg
A balance is an instrument used to determine mass

8. SOME REVIEW FOR YOU
Mass v. Weight

9. REVIEW
Length = the distance covered by a straight line segment between two points
Measured in meters (m)
Time – interval between two occurrences
Measured in seconds (s)

10. SOME REVIEW FOR YOU
Temperature = the average kinetic energy of the particles that make up matter.
Measured in Kelvin (K)
Kelvin is a scale based on molecular motion.
We also use Celsius (oC)
To convert from (oC) to K:
K = (oC)
(oC) = K –

11. SOME REVIEW FOR YOU Example problem: convert 25oC to Kelvin 298 K
Example problem: convert 400 Kelvin to oC
127 oC

12. SOME REVIEW FOR YOU Scientific Notation
Used in science because scientist often work with very large or very small numbers
Ex: Astronomers, Bacteriologists, Chemists

13. SOME REVIEW FOR YOU
To add and subtract numbers that are in scientific notation you have to:
Be sure numbers are in the same units
NOT one in grams and one in kilograms
Be sure the numbers are to the same power
Examples:
2.30 X X 1014 = __________
1.14 X 107 – 3.11 X 109 = __________

14. SOME REVIEW FOR YOU
To multiply or divide numbers that are in scientific notation you have to:
Add exponents if you are multiplying
Subtract exponents if you are dividing
Examples
(6.87 X 1087) (8.24 X 1073) = _________
(4.87 X 1036) / (8.55 X 1021) = ________

15. HOMEWORK
GCWS 2A

16. (More) Uncertainty
Recall: in chemistry (or any science) we deal with a lot of uncertainty.
Question: how else do we handle uncertainty?
Answer: Calculations like percent error and significant digits allow scientist to see how far off they may be.

17. Uncertainty Percent Error: is calculated as seen below
Percent Error = Experimental value – Theoretical value X 100
Theoretical value
Because absolute value is used % error will always be a positive number.

18. Uncertainty
Ex: what is the % error of an experiment where a student produces 43 g of sodium sulfite from the reaction including sodium, sulfur and oxygen? The theoretical mass of sodium sulfite was 49.2 g.
12.6 %
Ex: what is the % error of an experiment where a student observed that the time a certain reaction lasted was s? The theoretical time that was calculated was s.
1.53%

19. MORE HOMEWORK
DO GCWS 2C

20. Uncertainty
What is the measurement below?
11.65 cm

21. Uncertainty All measurements are approximates. Example
Sig figs allow us to be honest about how precise are measurements are
Example
Postage Scale: 3 g - precise to 1 significant figure
Two-pan balance: precise to 3 significant figures
Analytical balance: precise to g 4 significant figures
As we improve the sensitivity of the equipment used to make a measurement, the number of significant figures increases.

22. Uncertainty Significant Figures
Question: Which of the following measurements is the most precise? m
12 m

23. Uncertainty
Answer: m is more precise because what is being said is that this measurement was to the closest m opposed to being measured to the closest meter.
These numbers are not saying the same thing.
is saying the measurement is between m and m
12 is saying the measurement is between 11.5 m and 12.5 m
contains 5 significant digits whereas 12 only contains 2
All numbers but the last ones are certain.

24. Uncertainty Determining Significant digits:
All non-zero numbers are significant
95.32  4 sig figs
Zeros after decimal points are significant
 5 sig figs
Zeros between non-zero numbers are significant
 10 sig figs
Zeros that are place holders are not significant
 2 sig figs
 4 sig figs

25. Uncertainty Adding and subtracting significant figures
Answer should have as many decimal places as the measured number with the smallest number of decimal places.
EX:

26. Uncertainty Multiplying and Dividing with significant figures
answer should have as many significant figures as the measured number with the smallest number of significant figures.
Ex:

27. Summary
What questions do you still have?
What was unclear?