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Welcome to CHEM 121: Survey of General Chemistry

Prof. Abdi Mohamed

Contact Info: Page 1 of Syllabus

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Chem 121, Welcome on Board!

Lecture 1 Outline Introduction

Course Organization and Procedures The Scientific Method Measurement and Scientific Notation Measured Numbers and Significant Figures Problem Solving

Dimensional Analysis Density Problems Temperature Conversions

The Seattle Times: Carbon monoxide poisoning sickens 13 in Seattle

http://seattlepi.nwsource.com/local/360902_co29.html

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Course Organization and Procedure

Meetings: All in AS1519Labs on Wednesdays

Lectures on Mon and first hours of Wednesdays

Your course grade will be computed as follows:

3 midterms (lowest dropped) 200 pts 32%

Cumulative Final 200 pts 32%

6 Quizzes (10 pts each, lowest dropped) 50 pts 8%

8 Homeworks (3 WebCT HBA assignments) 45 pts 7%

8 labs (2 WebCT quizzes for 60 pts, rest 40 pts) 100 pts 16%

Group Presentation (Lab Presentation) 20 pts 3%

Subjective Evaluation 15 pts 2%

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Past Student Performance

Grading Scale

Based on percent overall points (see syllabus, page 4)… No curving

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

A Range B Range C Range D/W/F Range

Fall 07 and Winter 08 Grades

Per

cent S

tuden

ts

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Spring Student Performance

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Musings on Straight Lectures

Are there problems with straight lecturing?

The advantages of working together:

- A doctor’s order is 0.125 mg of ampicillin. The liquid suspension on hand contains 250 mg/5.0 mL. How many milliliters of the solution are required?

- Alex is 34 years of age. How old is Alex in seconds?

http://www.youtube.com/watch?v=2luAeK0Tuu8

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Lecture Format

Active Learning: Get Engaged

Why group work? Why active learning?

Warm-up questions or quiz ~ 5–10 minutes

Short lecture ~ 15 minutes

Group activity ~ 10 minutes

Second Short lecture ~ 15 minutes

Active Learning (Individual/pair) ~ 10 minutes

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Comments from Prev. Quarters.

My Philosophy: Getting students engaged on course content facilitates learning and provides opportunities to correct misconceptions early on.

Research on learning: students need to be active for meaningful learning to transpire.

“It made me actually work with what I had just learned instead of listening and not really paying that good of attention. They really helped me.”

“I learned this way the best.” Not for everyone …Some hate it! (~ 5 to 10%)

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Feelings Towards Chemistry

“Chemistry was my last pre-req class and I put it off to the end because I thought I would be horrible at it and that I would hate it.”

“Chemistry is not for me.” “Neither of these turned out to be true.” “I enjoyed learning chemistry.”

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What you don’t have to worry about in this class … In the past, you may have memorized

formulas? Forget about that . . . All formulas will be available to you during

exams You are allowed to bring your own 4 x 6” index

card to all the midterms You are allowed to bring 8.5 x 11” sheet to the

final exam Applied knowledge, not memorization

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The Scientific Method: Overview

Four Steps:

1. Observation

2. Hypothesis

3. Experiment

4. Theory

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The Nature of Science Activity

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Measurement and Scientific Notation

Measurement gives us three things:

1) Value 2) Unit (dimension) 3) error (uncertainty)

In chemistry we Measure quantities. Do experiments. Calculate results. Use numbers to report

measurements.

Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Stating Measurements

In every measurement, a number is followed by a unit.

Observe the following examples of measurements:

Number and Unit

35 m

0.25 L

225 lb

3.4 hr

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Units in the Metric System

In the metric and SI systems, one unit is used for each

type of measurement:

Measurement Metric SI

Length meter (m) meter (m)

Volume liter (L) cubic meter (m3)

Mass gram (g) kilogram (kg)

Time second (s) second (s)

TemperatureCelsius (C) Kelvin (K)

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Some Units You Should Know

The inside back cover of your text lists some useful conversion factors. That page will be available to you during exams, but it is good idea to be familiar with these units anyway.

Length: 1 meter (m) = 100 centimeters (cm)

1 inch (in) = 2.54 cm (exact)

Volume: 1 liter (L) = 1000 milliliters (mL)

Mass: 1 kilogram (kg) = 1000 grams (g)

1 g = 1000 mg

1 kg = 2.20 Ib

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Prefixes and Scale

You should definitely learn this inside out. Again, these prefixes are given in the inside back cover of your text, which should be available to you on exam dates.

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A very large or a very small number can be expressed as a number between 1 and 10 and power of 10

Power of 10 can be either positive or negative.

coefficient power of ten coefficient power of ten 1.5 x 102 7.35 x 10-4

To write a number in scientific notation, the decimal point is placed after the first digit.

The spaces moved are shown as a power of ten.

52 000. = 5.2 x 104 0.00378 = 3.78 x 10-3

4 spaces left 3 spaces right

The Scientific Notation

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Comparing Numbers in Scientific and Standard formats

Here are some numbers written in standard format and in scientific notation

Number in

Standard Format Scientific Notation Diameter of the Earth

12 800 000 m 1.28 x 107 m

Mass of a human

68 kg 6.8 x 101 kg

Length of a virus

0.000 03 cm 3 x 10-5 cm

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Pause: Group Activity, On-the-Board Problem Session

Group activity: all groups work on problems on group activity 1 worksheet, problems 1-3

While working on the problems, ask if you have any questions. I’m more than happy to help

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Measured Numbers

Two types of numbers:

1) Measured numbers: obtained by measuring quantities

2) Exact numbers: obtained by counting, defined numbers

Come up with examples involving measured number and exact numbers:

Measured Numbers Exact Numbers

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Significant Figures (SF) in Calculations: A Guided-Inquiry Exercise

Study the following examples and determine the rules for rounding off numbers. First, what does it mean to round a number?

5.304 becomes 5.3 when rounded

110.548 becomes 110.5 when rounded

Okay, so what is the rule for rounding?

The rule is:

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Determining Significant Figures

TABLE 1.4

Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings

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All non-zero numbers in a measured number are significant.

Measurement Number of Significant Figures

38.15 cm 4

5.6 ft 2

65.6 lb 3

122.55 m 5

Counting Significant Figures

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Sandwiched zeros Occur between nonzero numbers. Are significant.

Measurement Number of Significant Figures

50.8 mm 32001 min 40.0702 lb 30.40505 m 5

Sandwiched Zeros

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Leading zeros Precede non-zero digits in a decimal number. Are not significant.

Measurement Number of Significant Figures

0.008 mm 1

0.0156 oz 3

0.0042 lb 2

0.000262 mL 3

Leading Zeros

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Trailing zeros

Are zeros at the right end of number

Are significant ONLY if the number contains decimal

If the number has NO decimal, these are NOT SF

Measurement Number of Significant Figures

25000 cm 2 2.00 kg 3 48 60.0 mL 5

25 005 000 g 5480. 3

Trailing Zeros

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Significant Figures in Scientific Notation

In scientific notation All digits including zeros in the coefficient are

significant.

Scientific Notation Number of Significant Figures

8 x 104 m 1

8.0 x 104 m 2

8.00 x 104 m 3

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State the number of significant figures in each of the following measurements:

A. 0.030 m

B. 4.050 L

C. 0.0008 g

D. 2.80 m

Consult with someone sitting next to you.

Learning Check

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A. Which answer(s) contains 3 significant figures? 1) 0.4760 2) 0.00476 3) 4.76 x 103

B. All the zeros are significant in

1) 0.00307 2) 25.300 3) 2.050 x 103

C. The number of significant figures in 5.80 x 102 is

1) one 2) two 3) three

Learning Check

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In which set(s) do both numbers contain the same number of significant figures?

1) 22.0 and 22.00

2) 400.0 and 4.00 x 102

3) 0.000015 and 150 000

Learning Check: You Decide

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Significant Figures (SF) in Calculations: A Guided-Inquiry Exercise

Look at the following example involving multiplication or division:

M/D: 110.5 x 0.048 = 5.304 = 5.3 (rounded)

4 SF 2 SF calculator 2 SF

How did you determine how many sig. figs our answer should have?

Now, what about addition or subtraction: here is an example:

A/S: 110.5 + 0.048 = 110.5 (rounded)

How is sig. figs in final answer determined?

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Pause: Think Aloud Pair Problem Solving (TAPPS)

Work with some one sitting next to you on ALE 1 worksheet, problems 1-5. YOU HAVE 5 MINUTES

Alternative in answering the questions

One of you solves one problem out-load, sharing your thinking process as you solve the problem with your partner; the other listens, giving you feedback as necessary. Start with problem 1

On the next problem, switch roles. The listener become problem-solver and vice versa

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Pause: Individual Learning Exercise

Work on your own problems 6-10 of ALE 1. You have 5 minutes. Go.

Now, check your answers with someone sitting next to you. Reconcile any differences you may have

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Problem Solving: Dimensional Analysis

Trick is to identify correct equivalent statement(s) 1 m = 1000 mm

1 lb = 16 oz

2.20 lb = 1 kg

Obtain fraction from equality; write as numerator and denominator (ratio)

Ratio can be inverted to give two conversion factors for each equality

1 in. And 2.54 cm 2.54 cm 1 in.

Correct conversion factor cancels some units and leaves desired units

When done check for SF and SENSE

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Table 1.9: Some Common Equalities

Quick examples:

1) Convert 6 hours to second. (2) How many m in 524 cm?

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Problem Solving: Density

Density

Compares the mass of an object to its volume.

Is the mass of a substance divided by its volume.

Density expressionD = mass = g or g = g/cm3 volume mL cm3

Note: 1 mL = 1 cm3

Table 1.10 shows densities for common materials

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Pause: Group Activity Exercise

Group activity: all groups work on ALE 1 worksheet, problems 11-18, skip # 15

While working on the problems, ask if you have any questions. I’m more than happy to help

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Problem Solving: Temperature Conversions

Temperature scales Fahrenheit (oF)

Celsius (oC)Kelvin (K)

Have reference points for the boiling and freezing points of water.

Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Temperature Conversion Formulas

On the Fahrenheit scale, there are 180°F between the freezing and boiling points and on the Celsius scale, there are 100°C, thus a ratio of 1.8oF/1oC

Zero points are different

Conversion Factors

TF = 1.8 TC + 32

TT - 32

CF18.

TC = TK - 273

TK = TC + 273

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Pause: Individual/Group Learning Exercise

Work on problems 4-9 on group activity on your own first, then work as group on the same problems

While working on the problems, ask if you have any questions. I’m more than happy to help

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Write the initial and final units. Write a unit plan to convert the initial unit to the final

unit. Write equalities and conversion factors. Use conversion factors to cancel the initial unit and

provide the final unit.

Unit 1 x Unit 2 = Unit 2Unit 1

Initial x Conversion = Final unit factor unit

Dimensional Analysis: An In-depth Look

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Setting up a Problem

How many minutes are 2.5 hours?

Initial unit = 2.5 hr

Final unit= ? min

Plan = hr min

Setup problem to cancel hours (hr).

Initial Conversion Finalunit factor unit

2.5 hr x 60 min = 150 min (2 SF)

1 hr

Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings

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A rattlesnake is 2.44 m long. How many centimeters long is the snake?

1) 2440 cm

2) 244 cm

3) 24.4 cm

Pause: TAPPS Exercise

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Often, two or more conversion factors are required to obtain the unit needed for the answer.Unit 1 Unit 2 Unit 3

Additional conversion factors are placed in the setup to cancel each preceding unit Initial unit x factor 1 x factor 2 = Final unitUnit 1 x Unit 2 x Unit 3 = Unit 3

Unit 1 Unit 2

Using Two or More Factors

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How many minutes are in 1.4 days?

Initial unit: 1.4 days

Factor 1 Factor 2

Plan: days hr min

Example: Problem Solving

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Be sure to check your unit cancellation in the setup. The units in the conversion factors must cancel to

give the correct unit for the answer.

What is wrong with the following setup?1.4 day x 1 day x 1 hr

24 hr 60 min

Units = day2/min is not the unit needed

Units don’t cancel properly.

Check the Unit Cancellation

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A bucket contains 4.65 L of water. How manygallons of water is that?

Unit plan: L qt gallon

Equalities: 1.06 qt = 1 L 1 gal = 4 qt

Pause Group Work

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If a ski pole is 3.0 feet in length, how long is the ski pole in mm?

More Group Work

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If your pace on a treadmill is 65 meters per minute,

how many minutes will it take for you to walk a

distance of 7500 feet?

Individual Learning Check