Definition of Chemistry Chemistry is the study of substances in terms of: Composition What is it...

Definition of Chemistry

Chemistry is the study of substances in terms of:

• Composition What is it made of?

• Structure How is it put together?

• Properties What characteristics does it have?

• Reactions How does it behave with other substances?

Chemicals in Toothpaste

Matter

Matter

• Is what all materials are made of

• Has mass

• Occupies space

• Has characteristics called physical and chemical properties

Physical PropertiesCopper has physical properties:

• Reddish-orange

• Very shiny

• Excellent conductor of heat and electricity

• Solid at 25C

• Melting point 1083C

• Boiling point 2567C

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Physical properties are characteristics observed or measured without changing the identify of a substance: shape, physical state, odor and color.

States of Matter

All substances known as matter exist in one of three forms or states:

• Solids

Have definite volumes and shapes• Liquids

Have definite volumes, but take the shapes of containers

• Gases

Have no definite volumes or shapesCopyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

A physical change occurs in a substance if there is a change in the state or in the physical shape.

Physical Change

Examples of physical changes:

•Paper torn into little pieces (change of size)•Copper hammered into thin sheets•Water evaporating (change of state)•Water poured into a glass (change of shape)

Chemical Properties Chemical properties describe the ability of a

substance to interact with other substances or to change into a new substance.

Example:

Iron has the ability to form rust

when exposed to oxygen.


Chemical Change

In a chemical change or chemical reaction, a new substance forms

that has

• A new composition

• New chemical properties

• New physical propertiesCopyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

**DEMO

Classify each of the following changes as physical or chemical:

A. Bleaching a white shirt

B. Ice melting on the street

C. Toasting a marshmallow

D. Cutting a pizza

E. Iron rusting on an old car

Scientific Method


At a popular restaurant, where Chen is the head chef, the following occur:

• Chen notices that sales of the chef’s salad have dropped.• Chen decides that the chef’s salad needs a new dressing.• In a taste test, four bowls of salad are prepared with four new dressings:

sasame seed, oil and vinegar, blue cheese and anchovies.• The tasters rate the dressing with the sesame seeds the best.• After two weeks with the new dressing, Chen notices that the orders for the

chef’s salad have doubled.• Chen decides that the sesame dressing improved the sales of the chef’s

salad because the sesame dressing improved the taste of the salad.

Chapter 2 Measurements

Measurement

You make a measurement every time you:

• Measure your height • Read your watch• Take your temperature• Weigh a cantaloupe


Stating a Measurement

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

Units in the Metric SystemIn the metric and SI systems, one unit is used for each type of measurement:

Measurement Metric SILength meter (m) meter (m)Volume liter (L) cubic meter (m3)Mass gram (g) kilogram (kg)Time second (s) second (s)Temperature Celsius (C) Kelvin (K)

Scientific Notation

Scientific notation • Is used to write very large

or very small numbers• For the width of a human

hair of 0.000 008 m is written as:

8 x 10-6 m• Of a large number such as 2 500 000 s is written as:

2.5 x 106 s Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Comparing Numbers in Standard and Scientific Notation

Here are some numbers written in standard format

and in scientific notation:

Number in

Standard Format Scientific Notation

Diameter of Earth

12 800 000 m 1.28 x 107 m

Mass of a human

68 kg 6.8 x 101 kg

Length of a pox virus

0.000 03 cm 3 x 10-5 cm

Select the correct scientific notation for each.

A. 0.000 008

1) 8 x 106 2) 8 x 10-6 3) 0.8 x 10-5

B. 72 000

1) 7.2 x 104 2) 72 x 103 3) 7.2 x 10-4

Solution

Select the correct scientific notation for each.

A. 0.000 008

2) 8 x 10-6

B. 72 000

1) 7.2 x 104

Write each as a standard number.

A. 2.0 x 10-2

1) 200 2) 0.0020 3) 0.020

B. 1.8 x 105

1) 180 000 2) 0.000 018 3) 18 000

Solution

Write each as a standard number.

A. 2.0 x 10-2

3) 0.020

B. 1.8 x 105

1) 180 000

. l2. . . . l . . . . l3 . . . cm

• The markings on the meter stick at the end of the blue line are read as:

The first digit 2 plus the second digit 2.7

• The last digit is obtained by estimating. • The end of the line might be estimated between 2.7–

2.8 as half-way (0.5) or a little more (0.6), which gives a reported length of 2.75 cm or 2.76 cm.

Reading a Meter Stick

Known + Estimated Digits

In the length reported as 2.76 cm, • The digits 2 and 7 are certain (known)• The final digit 6 is estimated (uncertain)• All three digits (2.76) are significant including the

estimated digit

Significant Figures

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

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

A. 0.030 m 2

B. 4.050 L 4

C. 0.0008 g 1

D. 2.80 m 3

Solution

Rounding Off Calculated Answers

In calculations,

• Answers must have the same number of significant figures as the measured numbers.

• Often, a calculator answer must be rounded off.

• Rounding rules are used to obtain the correct number of significant figures.


Rounding Off Calculated Answers

When the first digit dropped is 4 or less,

• The retained numbers remain the same.

45.832 rounded to 3 significant figures

drops the digits 32 = 45.8

When the first digit dropped is 5 or greater,

• The last retained digit is increased by 1.

2.4884 rounded to 2 significant figures

drops the digits 884 = 2.5 (increase by 0.1)

Adding Significant Zeros

• Sometimes a calculated answer requires more significant digits. Then one or more zeros are added.

Calculated AnswerZeros Added to Give 3 Significant

Figures

4 4.001.5 1.500.2 0.200

12 12.0

Adjust the following calculated answers to give

answers with three significant figures.

A. 824.75 cm

B. 0.112486 g

C. 8.2 L

Solution

Adjust the following calculated answers to give answers

with three significant figures.

A. 825 cm First digit dropped is greater than 5.

B. 0.112g First digit dropped is 4.

C. 8.20 L Significant zero is added.

Calculations with Measured Numbers

In calculations with

measured numbers,

significant figures or

decimal places are

counted to determine

the number of figures in

the final answer. Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

When multiplying or dividing, use

• The same number of significant figures as the measurement with the fewest significant figures.

• Rounding rules to obtain the correct number of significant figures.

Example:

110.5 x 0.048 = 5.304 = 5.3 (rounded)

4 SF 2 SF calculator 2 SF

Multiplication and Division

When adding or subtracting, use

• The same number of decimal places as the measurement with the fewest decimal places.

• Use rounding rules to adjust the number of digits in the answer.

25.2 one decimal place

+ 1.34 two decimal places

26.54 calculated answer

26.5 answer with one decimal place

Addition and Subtraction

For each calculation, round the answer to give thecorrect number of significant figures.

A. 2.19 x 4.2 =

1) 9 2) 9.2 3) 9.198

B. 4.311 ÷ 0.07 =

1) 61.59 2) 62 3) 60

C. 235.05 + 19.6 + 2 = 1) 257 2) 256.7 3) 256.65

D. 58.925 - 18.2 =1) 40.725 2) 40.73 3) 40.7

A. 2.19 x 4.2 = 2) 9.2 B. 4.311 ÷ 0.07 = 3) 60 C. 235.05 +19.6 + 2 256.65 rounds to 257 Answer (1)

D. 58.925 -18.2

40.725 rounds to 40.7 Answer (3)

Solution

*****

Exact Numbers

• Exact numbers are NOT measured and do NOT have a limited number of significant figures. They do NOT affect the number of sig figs in a calculated answer.

Metric and SI Prefixes

Indicate the unit that completes each of the followingequalities:

A. 1000 m = 1) 1 mm 2) 1 km 3) 1 dm

B. 0.001 g = 1) 1 mg 2) 1 kg 3) 1 dg

C. 0.1 s = 1) 1 ms 2) 1 cs 3) 1 ds

D. 0.01 m = 1) 1 mm 2) 1 cm 3) 1 dm

Indicate the unit that completes each of the following

equalities:

A. 1000 m = 1 km (2)

B. 0.001 g = 1 mg (1)

C. 0.1 s = 1 ds (3)

D. 0.01 m = 1 cm (2)

Solution

Some Common Equalities

A conversion factor

• Is a fraction obtained from an equality

Equality: 1 in = 2.54 cm

• Is written as a ratio with a numerator and denominator

• Can be inverted to give two conversion factors for every equality

1 in and 2.54 cm 2.54 cm 1 in

Conversion Factors

Setting Up a Problem

How many minutes are 2.5 hours?Given unit = 2.5 hrNeeded unit = ? minUnit Plan= hr min

Set up problem to cancel hours (hrs).

Given Conversion Neededunit factor unit2.5 hr x 60 min = 150 min (2 SF) 1 hr


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

1) 2440 cm

2) 244 cm

3) 24.4 cm

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

2) 244 cm

2.44 m x 100 cm = 244 cm

1 m

Solution

• 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.Given unit x factor 1 x factor 2 = needed unitUnit 1 x Unit 2 x Unit 3 = Unit 3

Unit 1 Unit 2

Using Two or More Factors

How many minutes are in 1.4 days?

Given unit: 1.4 days

Factor 1 Factor 2

Plan: days hr min

Set up problem:

1.4 days x 24 hr x 60 min = 2.0 x 103 min

1 day 1 hr

2 SF Exact Exact = 2 SF

Example: Problem Solving

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

3.0 ft x 12 in x 2.54 cm x 10 mm =

1 ft 1 in. 1 cm

Calculator answer: 914.4 mm

Needed answer: 910 mm (2 SF rounded)

Check factor setup: Units cancel properly

Check needed unit: mm

Solution

Definition of Chemistry Chemistry is the study of substances in terms of: Composition What is it...

Documents

Transcript of Definition of Chemistry Chemistry is the study of substances in terms of: Composition What is it...