CHEMISTRY =

Chemistry is the study of matter and energy and the interactions between them

Studying science requires that one be a good observer.

observation inference

involves a judgmentor assumption

uses the fivesenses

Observations

DataObservations are also called data.

There are two types of data.

qualitative data quantitative data

descriptions; measurements; no numbers must have numbers

and UNITS

How good are the measurements?

• Scientists use two word to describe how good the measurements are-

• Accuracy- how close the measurement is to the actual value.

• Precision- how well can the measurement be repeated.

Differences

• Accuracy can be true of an individual measurement or the average of several.

• Precision requires several measurements before anything can be said about it.

PRECISION VERSUS ACCURACY

Problem : Identify if the following figures are either accurate or precise or

both:

• A._________ B._________ C.__________ D._________A ? Both A & P Only

Precise Neither A/P

In terms of measurement

• Three students measure the room to be 10.2 m, 10.3 m and 10.4 m across.

• Were they precise?• Were they accurate?

Data

• Must be organized

• Can be organized into charts, tables, or graphs

Line Graphshows continuous change

0

10

20

30

40

50

60

Jan Feb Mar Apr

Month

Sh

are

Pri

ce (

$)

Stock Price over Time

Elements of a “good” line graph

• axes labeled, with units

• use the available space

• title• neat

Temp. v. Vol. for a Gas at Constant Pressure

0123456789

10

120 140 160 180 200 220 240

Temp. (K)

Vo

lum

e (

L)

How to read a graph• Interpolate - read

between data points• What volume would the

gas occupy at a temperature of 150 K?

• Extrapolate - read data beyond data points

• What volume would the gas occupy at a temperature of 260 K?

• Which do you have more confidence in? Why?

Temp. v. Vol. for a Gas at Constant Pressure

0123456789

10

120 140 160 180 200 220 240

Temp. (K)

Vo

lum

e (

L)

(independent variable)

(dep

ende

nt v

aria

ble)

7 L

~4 L

Line Graph

Mass (g)

Age (Year of Penny)

Mass (g)

Age (Year of Penny)

Mass (g)

Age (Year of Penny)

Mass (g)

Age (Year of Penny)

How does the mass of a penny change with age?

A B

C D

Hypothesis

• A suggested solution to the problem.

• Must be testable• Sometimes

written as If…Then… statements

• Predicts an outcome

Scientific Law vs. Scientific Theory

Law of Gravity

A theory tries to explain whyor how something happens.

A law states what happens.

Theory of GravityAtomic TheoryCollision Theory of Reactions

Significant Figures

• Numbers in science are used to measure • Measurements can only be taken to the least

precise level of the measuring device

4. 0.080

3. 5,280

2. 402

1. 23.50

Significant Figures

Counting Sig Fig Examples

1. 23.50

2. 402

3. 5,280

4. 0.080

4 sig figs, rule #

3 sig figs, rule #

3 sig figs , rule #

2 sig figs , rule # Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Rounding rules

• Look at the number behind the one you’re rounding.

• If it is 0 to 4 don’t change it.• If it is 5 to 9 make it one bigger.• Round 45.462 to four sig figs.• to three sig figs.• to two sig figs.• to one sig figs.

45.4645.54550

Watch the Sig Figs

• When rounding, you don’t change the size of the number.

• You should end up with a number about the same size (magnitude).

• Use place holders- they’re not significant.– Round 15253 to 3 sig figs– Round 0.028965 to 3 sig figs 15300

0.0290

Significant figures (cont’d)

• 98.748 __________

• 950.9 __________

• 0.08 __________

• 0.058 __________

• 8.097 __________

• 74.99 __________

Round to the tenths Round to the hundredths

# of sig figs in the answer is based on the # sig figs in least precise measurement.

Which is the least precise?7.22m or 7.22555 m

Significant FiguresCalculating with Sig Figs

Significant FiguresCalculating with Sig Figs

– Add/Subtract - The # with the lowest decimal value determines the place of the last sig fig in the answer.

• (This is the measurement that is the LEAST precise)

3.75 mL

+ 4.1 mL

7.85 mL

224 g

+ 130 g

354 g 7.9 mL 350 g

3.75 mL

+ 4.1 mL

7.85 mL

224 g

+ 130 g

354 g Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Significant FiguresCalculating with Sig Figs

– Multiply/Divide - The # with the fewest sig figs determines the # of sig figs in the answer.

• (This is the measurement that is the LEAST precise)

(13.91g/cm3)(23.3cm3) = 324.103g

324 g

4 SF 3 SF3 SF

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

MEASURING WITH ACCURACY AND PRECISION

Practice Measuring Length

4.5 cm

4.54 cm

3.0 cm

Timberlake, Chemistry 7th Edition, page 7

cm0 1 2 3 4 5

cm0 1 2 3 4 5

cm0 1 2 3 4 5

How to measure Mass

100 200 400300 5000

0 10 20 30 40 50 60 70 80 90

0 1 2 3 4 5 6 7 8 9 10

How to Measure Volume

50

40

30

20

10

0

Graduated Cylinder

Come in variety of sizes

measure milliliters

• Meniscus - the curve the water takes in the cylinder

How to Measure Volume50

40

30

20

10

0

Meaure at the bottom of the meniscus.

The Metric System

• The units of measurement in science are from the metric system.

• The three most common are mass (grams), volume (liters), and length (meters)

• The metric system utilizes these base units then adds prefixes to indicate values increasing or decreasing by a factor of 10.

Converting

k h D d c m• how far you have to move on this chart,

tells you how far, and which direction to move the decimal place.

• The box is the base unit, meters, Liters, grams, etc.

. . . . . . .

Converting

k h D d c m• In order to convert from one unit to another, set

up a proportion where the unknown (X) and the given (G) with their respective units of measurement are on top and the conversion factors are under in the right place.

. . . . . . .

)(unitfactor

)(

)(unitfactor

) (unit X

2

2

1

1 unitG

Metric Conversions

• 10cm = _____m

• 1mm = _____cm

• 10dL = _____mL

• 5 liters = _____mL

Metric Conversions

• 0.1dL = _____cL

• 1Kg = _____g

• 100 mm = _____cm

• 300,00mg = _____g

What about micro- and nano-?

• The jump in between is 3 places• Convert 15000 μm to m

• Convert 0.00035 cm to nm

k h D d c m μ n3 3

. . . . . . . . .

Scientific Notation

How wide is our universe?

210,000,000,000,000,000,000,000 miles(22 zeros)

This number is written in decimal notation. When numbers get this large, it is easier to write them in

scientific notation.

Powers of 10

• http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/

• http://www.powersof10.com/

Scientific Notation

A number is expressed in scientific notation when it is in the form

a x 10n

where a is between 1 and 10and n is an integer

Write the width of the universe in scientific notation.

210,000,000,000,000,000,000,000 milesWhere is the decimal point now?

After the last zero.Where would you put the decimal to make

this number be between 1 and 10?Between the 2 and the 1

2.10,000,000,000,000,000,000,000.

How many decimal places did you move the decimal?

23When the original number is more than 1,

the exponent is positive.The answer in scientific notation is

2.1 x 1023

1) Express 0.0000000902 in scientific notation.

Where would the decimal go to make the number be between 1 and 10?

9.02The decimal was moved how many places?

8When the original number is less than 1, the

exponent is negative.9.02 x 10-8

Write 28750.9 in scientific notation.

1. 2.87509 x 10-5

2. 2.87509 x 10-4

3. 2.87509 x 104

4. 2.87509 x 105

2) Express 1.8 x 10-4 in decimal notation.0.00018

3) Express 4.58 x 106 in decimal notation.4,580,000

On the graphing calculator, scientific notation is done with the button.

4.58 x 106 is typed 4.58 6

4) Use a calculator to evaluate: 4.5 x 10-5

1.6 x 10-2

Type 4.5 -5 1.6 -2

You must include parentheses if you don’t use those buttons!!

(4.5 x 10 -5) (1.6 x 10 -2)

0.0028125Write in scientific notation.

2.8125 x 10-3

5) Use a calculator to evaluate: 7.2 x 10-9

1.2 x 102

On the calculator, the answer is:6.E -11

The answer in scientific notation is 6 x 10 -11

The answer in decimal notation is 0.00000000006

6) Use a calculator to evaluate (0.0042)(330,000).

On the calculator, the answer is1386.

The answer in decimal notation is 1386

The answer in scientific notation is 1.386 x 103

7) Use a calculator to evaluate (3,600,000,000)(23).

On the calculator, the answer is:8.28 E +10

The answer in scientific notation is 8.28 x 10 10

The answer in decimal notation is 82,800,000,000

Write (2.8 x 103)(5.1 x 10-7) in scientific notation.

1. 14.28 x 10-4

2. 1.428 x 10-3

3. 14.28 x 1010

4. 1.428 x 1011

Write in PROPER scientific notation.(Notice the number is not between 1 and 10)

8) 234.6 x 109

2.346 x 1011

9) 0.0642 x 104

on calculator: 6426.42 x 10 2

Write 531.42 x 105 in scientific notation.

1. .53142 x 102

2. 5.3142 x 103

3. 53.142 x 104

4. 531.42 x 105

5. 53.142 x 106

6. 5.3142 x 107

7. .53142 x 108