1. Unit 1 Part 2: Measurement
Mr. Gates
Chemistry

2. Measurement
Measurement is a quantitative description of both a number and a unit.
Ex. 6 feet and 2 inches

3. Standards There needs to be standards in order for units to work.
The King’s foot.

4. Accuracy vs. Precision
Accuracy describes how close a measurement is to the accepted value
Precision describes how close a measurement is to other measurements taken.

5. Percent Error Percent Error expresses the accuracy of a measurement
%𝐸𝑟𝑟𝑜𝑟= (Actual value) –(Theoretical value) Theoretical value x 100
Practice: If a student weighs a sack of potatoes to be Ibs, but the label on the sack says it is 32.3Ibs, what is the percent error?

6. Significant Figures
All numbers in a measurement that can be known precisely plus one additional number that is estimated. Digits in a measurement that indicate the precision of an instrument used to take a measurement.

7. Examples (going for a walk)
3 miles (3 estimated)
1.9 miles (9 estimated)
1.91 miles (1 estimated)
1.918 miles (8 estimated)

8. Which Figures are Significant?
All nonzero digits are significant
Ex. 5.3 has two significant figures
Zeroes appearing in front (to the left) of a nonzero digit are NOT significant
Ex has three significant figures
Zeroes appearing in between two nonzero digits are ALWAYS significant
Ex has four significant figures
Zeroes appearing to the right of a nonzero number and after the decimal place are significant.
Ex has five significant figures
Zeroes to the right of nonzero digits and to the left of a decimal place are ambiguous.
Ex. 300 has ?? … it depends

9. Ambiguous Numbers???
200 miles
200 miles
200. miles
200.0 miles

10. Practice How many significant figures are in the following numbers?
.0891
109.3
6.0
0.0005
1.089
7.0020
.08340

11. Rules for Rounding
If the number to the right of the last significant figure is from 0-4, round down.
If the number to the right of the last significant figure is from 5-9, round up.
Examples:
rounded to three significant figures is 26.8
Rounded to four significant figures is 26.82
Practice:
Rounded to three significant figures?
Rounded to two significant figures?

12. Practice Round the number 34.1050 to: 2 sig figs 5 sig figs 4 sig figs
34.11
3 sig figs
34.1
Round the number to:
2 sig figs
0.054
5 sig figs
4 sig figs
3 sig figs
0.0540

13. Exceptions that Make the Rule
There is an UNLIMITED amount of sig figs in two circumstances.
Counted numbers
23 students in class (can’t have a fraction of a person)
Exact/defined quantities
12 inches in a foot
Like … (catching my breath)… …. To infinity and beyond zeroes

14. Sig Figs w/ Calculations
Addition or Subtraction The answer can have no more decimal places than the number with the least decimal places in the calculation. Ex = 3.36, but with proper sig figs the answer is… =3.4 Ex = , but with proper sig figs the answer is… = 11.39

15. Sig Figs w/ Calculations
Multiplication and Division
The answer can have no more sig figs than the number with the least amount of sig figs in the calculation.
Ex x 2.6 = 3.224, but with proper sig figs the answer is...
= 3.2
Ex x = , but with proper sig figs the answer is…
= 33.5

16. Scientific Notation
Scientific notation is a number written as the product of two numbers.
Follows the following format:
M x 10N
M is some number between 1 and 10
N is the amount of times the decimal places had to be moved.
N ≠ decimals

17. Putting #’s in Sci. Notation
Every time the decimal place is moved the exponent must move too.
M x 10N
If the decimal moves  then the exponent goes down
If the decimal moves  then the exponent goes up

18. In and Out
Put into scientific notation: ,840,000,000 Take out of scientific notation: 3.65 x x 10-4

19. Sig Figs and Sci. Notation
All of the numbers in proper scientific notation are significant… No ambiguous numbers!!!
2000 is 2.00 x 103 with three sig figs.

20. Addition/Subtraction in Sci. Notation
Adding and Subtracting:
Exponents must be the same!!!
EX: x 105
x 105
11.17 x 105 (not correct sig figs)
11.2 x 105 (not correct sci not.)
1.12 x 106

21. Multiplying/Dividing in Sci. Notation
Multiplying and Dividing:
EX: x 102
x 4.2 x 103
30.24 x 105 (not correct sig figs)
30. x 105 (not correct sci. not.)
3.0 x 106

22. International System of Measurement
Internationally used system of measurement known as the “Metric System”

23. Benefits of Using the Metric System
Scientist all over the world use this system.
They can share and understand each other’s work.
Based on multiples of ten. Makes for easier conversions.

24. SI Base units

25. Volume
The amount of space an object takes up.
Base unit is cm3

26. Mass The amount of matter in an object.
Base unit is the kg because the gram is too small.

27. Weight
The pull gravity has on the mass of an object.

28. Fluid Volume
When dealing with a fluid (gas or liquid) the most commonly used unit is the liter (L)
1ml = 1cm3

29. SI Prefixes

30. Dimensional Analysis
Method of converting from one unit to another of equal value using conversion factors.

31. Conversion Factors
These are fractions that are equal to one because the top is equal to the bottom despite the differing units.
Multiplying anything by one will not change the number.
Conversion factors spawn from two numbers that are equal to each other.
Ex. 100cm = 1m
100𝑐𝑚 1𝑚 or 1𝑚 100𝑐𝑚

32. Using Dimensional Analysis
How many mg are in 1.32kg?
= 𝑚𝑔
How many seconds are in your lifetime?
How many cases of pop will you drink in your lifetime?
1.32kg
1000g
1000mg
1kg 1g

33. Converting Complex Units
What is 19 in2 in ft2?