Daniel L. Reger Scott R. Goode David W. Ball

www.cengage.com/chemistry/reger

Chapter 1 Introduction to Chemistry

What is Science?

“Natural abilities are like natural plants; they need pruning by study.” – Sir Francis Bacon (1561-1626)

The Nature of Science and Chemistry

• • Definitions

Science:

knowledge • Sir Francis Bacon: “And thus knowledge itself is power” • Modern science, the acquisition of knowledge, is acquired by experience (experiment) •

Chemistry:

the study of matter and its interactions with other matter and with energy.

Chemistry and the Natural Sciences

The Scientific Method

•

Scientific method

: investigations that are guided by theory and earlier experiments.

•

Hypothesis

: a possible explanation for an event.

•

Law

: a statement that summarizes a large number of observations.

•

Theory

: an explanation of the laws of nature.

Matter

•

Matter

: anything that has mass and occupies space.

•

Mass

: the quantity of matter in an object.

•

Weight

: the force of attraction between an object and other objects.

Mass and Weight

Mass on moon and earth is the same.

Weight on moon and earth is the different.

Properties of Matter

•

Property

: anything observed or measured about a sample of matter.

•

Extensive property

: depends on the size of the sample.

• mass, volume •

Intensive property

: independent of sample size.

• density, color, melting or boiling point

Physical Properties and Changes

•

Physical properties

: can be measured without changing the composition of the sample.

• mass, density, color, melting point •

Physical change

: a change that occurs without changing the composition of the material.

• freezing, melting

Chemical Properties

•

Chemical properties

: describe the reactivity of a material.

• Natural gas burns in air; iron rusts.

•

Chemical change

: at least part of the material is changed into a different kind of matter.

• The digestion of sugar is a chemical change.

Practice

State if the underlined property or changes is intensive or extensive and chemical or physical.

a) The color of mercury is silvery.

b) The sample of iron rusts by reaction with oxygen.

c) The heat released by burning coal can power a city.

d) Water boils at 100 °C.

e) A new pencil is 10 inches long.

Classification of Matter

• •

Substances

- a material that is chemically the same throughout.

Two types of substances • Elements cannot be broken into simpler substances.

•

Compounds

can be broken down into elements.

Substances

•

Substance

: cannot be separated into component parts

by physical methods.

•

Compound

: a substance which can be separated into simpler substances

by chemical methods.

•

Element

: a substance which

cannot

be separated into simpler substances

by chemical methods.

Mixtures

•

Mixture

: matter that can be separated into simpler materials by physical methods.

•

Heterogeneous mixture

: composition of the mixture changes from one part to another.

•

Homogeneous mixture

or

solution

: composition of the mixture is uniform throughout.

•

Alloy

: a solution of a metal and another material (usually another metal).

Classification of Matter

Practice

Identify the following types of matter as elements, compounds, heterogeneous mixtures, or homogeneous mixtures.

a) b) c) d) Sodium chloride Stainless steel Chlorine soil

Measurement

• Most modern science depends on measurements • • Parts of a measurement • The object of the measurement • The value of the measurement • The units of the measurement • The reliability of the measurement Example “The mass of iron was 4.0501 grams • All parts MUST be present in an answer for complete credit!!

Accuracy and Precision

• Modern chemistry is largely based on experimental measurements. The confidence in measurements involves: •

Accuracy

: agreement of a measurement with the true value.

•

Precision

: agreement among repeated measurements of the same quantity.

Accuracy and Precision

accurate and precise accurate but not precise precise but not accurate neither accurate nor precise

Accuracy and Precision

Significant Figures

• The

number of significant figures

is the number of digits from the first non zero digit through the last reported digit.

• The uncertainty is at least ±1 unit in the last reported digit.

• • Leading zeros – zeros preceding the first non-zero digit are NEVER significant. Trailing zeros – a decimal point is the key.

• No decimal – trailing zeros are NOT significant • Decimal – trailing zeros ARE significant

Significant Figures

• Quantities that are not limited by significant figures: • counted numbers or tallies.

• defined numbers.

• the power of ten in exponential notation.

Significant Figures

• How many significant figures are present in each of the measured quantities?

• 0.0012

106 2006 900.0

1.0012

0.001060

Significant Figures

• Since trailing zeros in numbers without a decimal points may be confusing for significant figures

use scientific notation

.

• 100

1

x 10 2

1.0

x 10 2

1.00

x 10 2 1? Or should there have been a decimal?

1 2 3

Practice

• Determine the number of significant figures: 100.

30505 125,904,000 4.800 x 10 -3 100.0

437,000 4.80 x 10 -3 0.0048

Uncertainty in Addition and Subtraction

• • • The absolute uncertainty can be no smaller than the least accurate number.

12.0

2

- 10.

4

1.

62 1.6

• The answer should have no more decimal places than the least accurate number.

Uncertainty in Multiplication and Division • Answers should have no more significant figures than the least accurate number.

•

3121

# sig. digits

4

x

12

x

2

=

37

452 =

3.7

=

2

=

2

x 10 4

NOT 37!!!!!!

37000 is questionable

Mixed Operations

• Determine accuracy in the same order as the mathematical operations, # of significant digits are in

red.

•

3

m v = 2.79 g 8.34 mL - 7.58 mL =

3 3

density = 3.7 g/mL

2 3

2.79 g 0.76mL

2

• Be mindful of what your calculator gives you!!

Rounding

• • • Be cautious about rounding during multiple steps.

Keep more significant figures than you need in intermediate steps.

Ex: • 2.5 x 4.50 x 11.25 = ?

Practice

• Evaluate each expression to the correct number of significant figures.

(a) 4.184 x 100.620 x (25.27 - 24.16) (b) (c) 8.925 - 8.904

x 100% 8.925

9.6 x 100.65

+ 4.026

8.321

Practice

Calculate each to the correct number of significant figures .

a) 0.1654 + 2.07 - 2.114 b) 8.27 x (4.987 - 4.962) 9.5 + 4.1 + 2.8 + 3.175

c) 4 (4 is exact) 9.025 - 9.024

d) 9.025

Base Units in the SI

Quantity Length Mass Time Temperature Amount Unit

meter second kelvin mole

Electric current

ampere

Luminous intensity

candela

Abbreviation

m kilogram kg s K mol A cd

Common Prefixes Used With SI Units

Prefix mega kilo centi milli micro nano pico Abbreviation M k c m m n p Meaning 10 6 10 3 10 -2 10 -3 10 -6 10 -9 10 -12

Prefixes Used With SI Units

1 kilogram is equal to 1000 g.

Unit Conversion Factors

•

Unit conversion factor

: a fraction in which the numerator is a quantity equal or equivalent to the quantity in the denominator, but expressed in different units • The relationship 1 kg = 1000 g • Generates two unit conversion factors:    1 kg 1000 g    and    1000 g 1kg   

Unit Conversions

• • • Lets convert 5.73 g to kg.

Start with what you know!!!

Add conversion factors to cancel units • Units must be same on top & bottom to cancel 5 .

73

g

   1

kg

1000

g

   0.00573 kg grams on top grams on bottom

Practice

Convert the following: a) 17.43 km to cm b) 165 μg to kg

Conversion Among Derived Units

• • •

Volume

is the product of three lengths.

The standard unit of volume is the cubic meter (m 3 ).

100 cm = 1 m (100 cm) 3 10 6 cm 3 = (1 m) = 1 m 3 3 Two important non-SI units of volume are the liter and milliliter.

1 liter (L) = 1000 mL = 1000 cm 3 1 mL = 1 cm 3

Volume

Volumes can be expressed in different units depending on the size of the object .

1 m 3 contains 1000 L 1 L contains 1000 mL

Using Unit Conversions

• Express a volume of 1.250 L in mL, cm 3 , and m 3 1.250

L    1000 mL 1 L  1,250 mL 1.250

L    1000 cm 3 1 L    1,250 cm 3 1.250

L    1 10 6 m 3 cm 3    1,250  10 3 m 3

Density

• •

Density

: mass per unit volume d  m V • Density, in SI base units, is kg/m 3 (kg m -3 ).

• Most commonly used density units are g/cm 3 (g cm -3 or g/mL) for solids and liquids , and g/L for gases.

Conversions Between Equivalent Units

• The density of Ti is 4.50 g/cm 3 4.50 g = 1 cm 3 .

or • Calculate the volume of 7.20 g Ti.

What we know 7.20

g Ti     1 cm 3 4.50

g     1.60

cm 3 Ti Answer: √ number √ units √ object √ sig figs Units cancel

English System

Practice

a) Express 323 milliliters in gallons.

b) Express 3.61 cubic feet in cubic centimeters.

Temperature Conversion Factors

T F  T C    1.8

1.0

o o F C    32 o F T C T K   T F  32 o F     1.0

o 1.8

o C F    T C  273.15

For water 0 Kelvin 273 373 -273 o Celsius 0 o 100 o -460 o Fahrenheit 32 o 212 o

Practice

• Express 17.5

°C in °F and in K.

Practice

• It has been estimated that 1.0 g of seawater contains 4.0 pg of Au. The total mass of seawater in the oceans is 1.6x10

12 Tg, If all of the gold in the oceans were extracted and spread evenly across the state of Georgia, which has a land area of 58,910 mile 2 , how tall, in feet, would the pile of Au be?

Density of Au is 19.3 g/cm 3 . 1.0 Tg = 10 12 g.

Practice

• One metal object is a cube with edges of 3.00 cm and a mass of 140.4 g. A second metal object is a sphere with radius 1.42 cm and a mass of 61.6 g. Are these objects made of the same or different metals? Assume the calculated densities are accurate to 1.00%.

Practice

• • A 40-lb container of peat moss measures 14 x 20 x 30 in. A 40-lb container of topsoil has a volume fo 1.9 gal. Calculate the density of both the peat moss and the topsoil.

How many bags of peat moss are needed to cover an area measuring 10 ft x 20 ft x 2 in?

Practice

On a typical day, a hurricane expends the energy equivalent to the explosion of two thermonuclear weapons. A thermonuclear weapon has the explosive power of 1.0 Mton of nitroglycerin. Nitroglycerin generates 7.3 kJ of explosive power per gram of nitroglycerin. The hurricane’s energy comes from the evaporation of water that requires 2.3 kJ per gram of water evaporated. How many gallons of water does a hurricane evaporate per day?

THINK!!

Homework: OWL: All of the required assignments book: All questions from the end of the chapter are recommended as practice.