1. Unit 2: Measuring and Calculating
Chapter 2
“1000 grams...well it sounded like a lot when i orderd it. ah well, I cant make hide nor hair of these metric boobytraps”
My car gets fourty rods to the hogshead and that's the way I like it

2. Objectives By the end of this unit, you will be able to:
Distinguish between qualitative and quantitative characteristics
List three requirements for making a measurement
List and define the seven basic SI units with their categories of measurement
Define the commonly used SI prefixes
Define mass, weight, balance, and state the difference between mass and weight
Define temperature and give the basis for the Celsius temperature scale
Distinguish accuracy and precision

3. Objectives cont.
Define significant digits and counting numbers and determine the number of significant digits in a given measurement
Express results of math equations in significant digits
Convert numbers from decimal to scientific notation
Combine SI units to form derived units
Demonstrate use of logic to solve problems
Use the factor-label method to solve problems
Define density and perform calculations using density, mass, and volume

4. The International System (SI)
Qualitative measurement – a description with no measurement
Color
Smell
Quantitative measurement- a description with numerical information
Length
Mass

5. SI System continued… Three requirements for quantitative measurement
We must know exactly what property we are trying to measure
We must have some standard with which to compare whatever we are measuring
We must have some method of making this comparison

6. SI System continued…
The SI system is the standard measuring system used in science
SI is a modified version of the metric system
Most countries use SI or are converting to it
The SI system is very simple and consistent
The SI system has seven basic units…

7. Seven Basic Units of SI Quantity Unit Unit Symbol Length Meter m Mass
Kilogram kg
Time
Second s
Electric Current
Ampere A
Temperature
Kelvin K
Amount of substance
Mole
Mol
Luminous intensity
Candela cd

8. SI prefixes
In SI, prefixes are added to the base units to obtain different units of a convenient size for measuring larger or smaller quantities
Kilometer = 1000 meters
Millimeter = 1/1000 of a meter
You will need to memorize the metric prefixes and the values which they stand for
Next, a table of the metric prefixes…

9. SI Prefixes Prefix Symbol Meaning Multiplier Mega M Million 1,000,000
Kilo K
Thousand
1,000
Deci d
Tenth
0.1
Centi c
Hundredth
0.01
Milli m
Thousandth
0.001
Micro
Millionth
Nano n
Billionth
Pico p
Trillionth

10. Homework
Worth a possible 5 points
Due:

11. Mass and Weight What's the difference?
Weight is a measure of the force of gravity between two objects
On objects weight on Earth can change when the distance between the object and the center of the Earth changes
Mass is a measure of the amount of matter an object has
Mass never changes

12. Mass The SI unit for mass is the kilogram The Balance
In the lab, we usually use the gram (g), because a kilogram is too large
The mass of a paperclip is about 1.5 g
The Balance
The balance is the tool used to measure mass
Using the balance

13. Length
Length is the distance covered by a line segment connecting two points
The SI unit for length is the meter (m)
Length is usually measured with a ruler or similar device
Examples
A nickel has a diameter of ~2 cm
A notebook is about 25 cm long

14. Time Time is the interval between two occurrences
The SI unit for time is the second (s)
Time is usually measured with a clock or watch
The atomic clock is the most accurate tool for measuring time

15. Temperature
The temperature of a sample of matter is a measure of the average kinetic energy of the particles that make up the sample
The greater the kinetic energy, the higher the temperature
Temperature is usually measured with a thermometer
The SI unit for temperature is the Kelvin (k)
The Celsius scale is also often used
The Celsius scale is based on the boiling point and freezing point of water
It is related to the Kelvin scale. More later…

16. Accuracy Vs. Precision
Accuracy refers to how close a measurement is to the true or correct value for the quantity
Precision refers to how close a set of measurements for a quantity are to one another, regardless of whether the measurements are correct
Usually measurements that have precision are also accurate, but not always

19. Assignment Complete Exercises 1-2 on page 19 of your text
This assignment is worth 10 points
Due: By the end of class

20. Significant Digits (Sig Fig’s)
All digits that occupy places for which actual measurement was made are referred to as significant digits
The places actually measured include one uncertain, or estimated digit
See Figure 2-7 in your text

21. Sig Fig’s cont. The exactness of measurements is very important
This is determined by the number of significant digits in the measurement
There are a few rules for determining the number of significant digits in a recorded measurement
Counting numbers (an exception)
When something is counted (not measured) it is considered to have an infinite amount of significant figures (more on that later)

22. Sig Fig Rules Digits other than zero are always significant
96 g 2 sig figs
sig figs
sig figs
One or more final zeros used after the decimal point are always significant
km 5 sig figs
sig figs
Zeros between two other significant digits are always significant
5.029 m 4 sig figs
Zeros used solely for spacing the decimal point are not significant
7000 g 1 sig fig
kg 3 sig figs

23. Practice How many significant digits in each of the following? 30.4
2700
5.10
0.023
7.0200
3.00
2.700
0.0304
51.0

24. Assignment Complete Exercise 5 on page 24 of your text
This assignment is worth 5 points
Due: Tomorrow

25. Pop Quiz!!! Write the correct number of sig figs for the following:
g meters
m ,000 cd
kg g
4. 50,000.0 L km
cm pm
dm g
g ML
L L
mL g
cg pencils

26. Scientific Notation
Scientific Notation makes it easier to work with large numbers
In Scientific Notation all numbers are expressed as the product of a number between 1 and 10 and a whole-number power of 10
M x 10n
1,000 = 1 x 103
Using Scientific Notation also makes counting sig figs easier
8000 = 8 x sig fig
= x sig figs

27. Scientific Notation Practice
Convert the following to scientific notation
30,000
1,567
5.67
7,500,000

28. Scientific Notation Rules
To determine the number of digits that should appear in the answer to a calculation, we use two rules
In addition and subtraction, the answer may contain only as many decimal places as the measurement having the least number of decimal places
= 8.5
This answer should then be rounded off to the nearest tenth, so the answer would be 8.5
In Multiplication and division, the answer may contain only as many significant digits as the measurement with the least number of significant digits
1.1 x = 2.200
You can only have 2 significant digits, so your answer would be 2.2

29. Assignment Complete Exercises 6-12 on page 27 of your text
This will be worth a possible 10 points
Due: Tomorrow

30. Derived Units
By combining SI units, we can obtain measurement units to express other quantities
Distance divided by time = speed
Length x Length = area
Unit of area is the square meter (m2)
Area x Length = volume
Unit of volume is the cubic meter (m3)
Most often in lab we use the milliliter (mL) for volume
1000 cm3 = 1000 mL = 1 L = 1 (dm3)

31. Problem Solving 3 part method for solving problems
Decide what information is given
Decide what information is needed
Find a “bridge” that can help you use the information that you have to obtain the information that you need
The “bridge” is the information that you will learn studying chemistry

32. Conversion Factors A conversion factor is a ratio equivalent to one
Convert 72 cm to meters
100 cm = 1 meter
100 cm/100cm = 1m/100cm; therefore 1m/100cm is your conversion factor
72cm x 1 = 72cm x (1m/100cm)
So, 72cm = 72m/100 = 0.72 m
Convert 5.5 L to ml

33. Conversion Factors Cont.
Vertical bar
To make conversions easier, we can set off each factor by a vertical bar
Convert 5 dm3 to cm3

34. Factor Label Method
In the factor label method, units are treated as factors, and as such, can be divided out
Example on board

35. Density Density is mass per unit of volume Density = mass/volume D=m/v
Unit is g/ml

36. Assignment Complete Exercises 13-24 on pages 30-31
Exercises 29, 32, 38, and 39 on page 32 of the text
Exercises 44, 45,46 on page 35 of your text
Worth 20 points
Due: Monday

37. Chapter Review Complete chapter review questions
48 all, 49a, 50 all, 51 all, 54, 55, 57, 59, 60, 61, 62, 64, 65, 66 all, 68 all, 69 all, 70, 71 all, 73 all, 83, 85, 86, 94, and 95 on pages of your text
Remember, these questions will be very similar to those found on the unit test, so do them all
This will be collected for a possible 25 points