Download Sig. Fig. & Temperature Slides

Chapter 3:
Temperature, Proportions,
Density, Problem Solving
Sections 3.6 - 3.10
Chemistry 111
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Topics
• Probably won’t Finish Chapter 3 Today
– 1st set of workbook problems will be due Thursday 7/8
(you should have started them already)
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•
•
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Significant Figures
Temperature Lecture
Temperature Exercise
Problem Solving:
– Identify Knowns & Unknowns
– Per Paths
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Chapter 3 - Exercise #1 (Recap)
How many m are there in 2 miles?
a. miles  km  m  m
b. miles  ft  in  cm  m  m
To Solve:
(1) Find all of your conversion ratios (PERs) &
write them out (one for each arrow).
(2) Start with the given & write out the problem.
(3) Punch in the numbers.
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Chapter 3 - Exercise #1 (Recap)
miles  km  m  m
 1 miles   1 km   106 m 
 1m 
, or  6

,  3 , 

 1.609 km   10 m   1 m 
 10 m 
 1.609 km   103 m   1 m 
   6   3.2 109
  
2 miles  
 1 miles   1 km   10 m 
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Chapter 3 - Exercise #1 (Recap)
miles  ft  in  cm  m  m
 1 miles   1 ft   1 in   1 cm   106 m 


, 
, 
,  2 , 
 5280 ft   12 in   2.54 cm   10 m   1 m 
 5280 ft   12 in   2.54 cm   10 2 m   1 m 
   6 
  
  
  
2 miles  
 1 miles   1 ft   1 in   1 cm   10 m 
 3.2 109
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Counting Significant Figures
1. Nonzero Integers. Nonzero integers always count as
significant figures.
2. Zeros. There are three classes of zeros:
1. Leading Zeros are zeros that precede all the nonzero digits.
These do not count as significant figures. In the number 0.0056,
the three zeros simply indicate the position of the decimal point.
This number has only two significant figures.
2. Captive Zeros are zeros between nonzero digits, these always
count as significant figures. The number 5.009 has four
significant figures.
3. Trailing Zeros are zeros at the right end of the number. They are
significant only if the number contains a decimal point.
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Counting Significant Figures
Note 1: In Scientific notation, all digits in
the coefficient are significant
figures.
Note 2: Exact numbers can be considered to
have a  (infinite) number of
significant figures.
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Rules for Computations & Sig. Figs.
1.
For multiplication and division, the number of
significant figures in the result is the same as the number
with the least precise measurement used in the
calculation. For example:
5.667 × 4.1 = 24.234
2.
For addition and subtraction, the
result has the same number of
decimal places as the least precise
measurement used in the
calculation. Set the problem up
like 2nd grade math!

24
5.11
20.5
+ 2.812
28.422  28.4
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Rules for Computations & Sig. Figs.
Note 1: For multiplication and division – the
sig. figures are counted.
Note 2: For addition and subtraction – the
decimal places are counted.
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Temperature Scales
• Fahrenheit (°F)
• U.S. Weather
• Celcius (°C)
• Chem. Lab, Metric
Weather
• Kelvin (K)
• Science Lab,
especially gases.
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Fahrenheit & Celcius
Fahrenheit
212°
Lotsa
Steps
(180)
32°
Celcius
Boil
RATIO OF STEPS
IS EXACTLY:
180
1.8
9
——— = ——— = —
100
1.0
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Freeze
100°
Nice #
of steps
(100)
0°
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Kelvin
• Same scale as Celcius
• Never use the degree symbol °
• Starts at Absolute Zero
– 0.0 K = absolute zero
– 273.15 K = 0.0 °C
– All molecular motion is stopped at absolute
zero.
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Team Exercise #1 – Sample
Fahrenheit (°F)
Celcius (°C)
Kelvin (K)
Why it’s
Important
25
0.0
77.3
98.6
32
451
107
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Team Exercise #1 – 20 Minutes
• Develop a table of your favorite / important
temperatures. Determine the temperature (with
sig. figs.) in °C, °F, and K at each of these
temperatures.
– Chemically important: 25 °C, 0.0 K, 77.3 K
– Life important: 98.6 °F, 32 °C, 451 °F, 107 °F
– Your favorite: ________, _______, _______
• Don’t forget:
– Do one sheet of paper.
– Put everyone’s name on it.
– Fill in your log sheet.
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Problem Solving
List all "givens," including units.
List all units of wanted quantities.
Decide how to solve the problem.
Dimensional
Analysis
Algebra
Write the PER/PATH
Solve the equation for
the wanted quantity.
Write the calculation setup.
Include Units.
Substitute all given values.
Include Units.
Calculate the answer.
Calculate the answer.
Check the answer. Are the
units correct? Is the number
reasonable.
Check the answer. Are the
units correct? Is the number
reasonable.
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Writing PER/PATHS
• This needs practice! I’ll do a few, you’ll do
a few.
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Writing PER/PATHS (2)
• A woman gives birth to a 7.5-lb baby. How
would a hospital using metric units record
this baby’s mass?
Start: lb
End: kg
Path: lb – oz – g – kg
16 oz 28.35 oz 1 kg
Conversions:
,
, 3
1 lb
1g
10 g
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Writing PER/PATHS (3)
• How many grams of milk are in a 12.0
fluid-ounce glass?
Start: fl.oz.
End: g
Path: fl.oz.– qt – gal – ft3 – lb – g
Conversions:
32 floz 1 gal 7.48 gal 64.4 lb
1 lb
,
,
,
,D
3
3
1 qt
4 qt
1 ft
1 ft
453.6 g
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Writing PER/PATHS (4)
• Standard typewriter paper in the United
States is 8½ in. x 11 in. What is the area in
centimeters?
• Start: in
End: cm2
Path: in  in2 – cm2
Conversion:
2.54 cm 2.54 2 cm 2
A  lw,
1 in
,
2
1 in
2
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Team Work #2
• Work on book homework as a team BUT…
– Follow the organization in Figure 3.9.
– Work as a team on 1 sheet of paper & turn it in
at the end of class.
– Full credit Points for getting at least 2 done.
– Use 1 sheet of paper for each problem.
• Do these (from book HW assignment):
– 28, 31, 35, 50
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