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Chapter 3: Temperature, Proportions, Density, Problem Solving

Sections 3.6 - 3.10

Chemistry 111

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3

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)

• 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

m

mor

m

m

m

km

km

miles

6

6

3 10

1,

1

10,

10

1,

609.1

1

96

3

102.310

1

1

10

1

609.12

m

m

km

m

miles

kmmiles

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Chapter 3 - Exercise #1 (Recap)

miles ft in cm m m

m

m

m

cm

cm

in

in

ft

ft

miles

1

10,

10

1,

54.2

1,

12

1,

5280

1 6

2

9

6

2

102.3

10

1

1

10

1

54.2

1

12

1

52802

m

m

cm

m

in

cm

ft

in

miles

ftmiles

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Counting Significant Figures1. 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 24

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!

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)

• Celcius (°C)

• Kelvin (K)

• U.S. Weather

• Chem. Lab, Metric Weather

• Science Lab, especially gases.

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RATIO OF STEPSIS EXACTLY:

180 1.8 9——— = ——— = —100 1.0 5

Fahrenheit & CelciusFahrenheit Celcius

32° Freeze 0°

LotsaSteps (180)

Nice # of

steps (100)

212° Boil 100°

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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 – SampleFahrenheit (°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

D ecide how to so lve the prob lem.

Check the answ er. A re theunits co rrect? I s the num ber

reasonable.

Calcu late the answ er.

W rite the calcu lation setup.I nclude Units.

W rite the P ER / P A T H

D im ensionalA nalysis

Check the answ er. A re theunits co rrect? I s the num ber

reasonable.

Calcu late the answ er.

Substitute all g iven values .I nclude Units.

So lve the equation forthe w anted quantity .

A lgebra

L ist a ll un its o f w anted quantities .

L ist a ll "g ivens," includ ing un its .

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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

Conversions: g

kg

g

oz

lb

oz310

1,

1

35.28,

1

16

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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: gPath: fl.oz.– qt – gal – ft3 – lb – g Conversions:

g

lbD

ft

lb

ft

gal

qt

gal

qt

floz

6.453

1,

1

4.64,

1

48.7,

4

1,

1

3233

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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:

22

22

1

54.2,

1

54.2,

in

cm

in

cmwlA

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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