Course: General Chemistry I (CHEM 140, Section: 02)Instructor: Cevdet Akbay Office location: LS 227Office phone: 672-1943Office hours: MTWRF 10:00 AM-12:00 PM or by appointments

Chemistry: The Study of Change

Chapter 1

 

Why ice melts and water evaporates? Why keeping foods cold slows their spoilage?

How our bodies use food to maintain life?

Why leaves turn colors in the fall? How a battery generates electricity?

How Blah blah blah

Chemistry supplies answers to these questions and countless others like them. Then, how we define Chemistry? It depends:

Chemistry is the scientific discipline that treats the composition, properties, and transformations of matter.

Chemistry is the study of the properties of materials and the changes that materials undergo.

You are just beginning the journey of learning chemistry.

One of the joys of learning chemistry is seeing how chemical principles operate in all aspects of our lives, from lighting a match to the development of drugs to cure cancer.

This first chapter provides an overview of what chemistry is about and deals with some fundamental concepts of matter and scientific measurements.

1. Matter is anything that occupies space and has mass.

2. A substance is a form of matter that has a definite composition and distinct properties.

Chemistry is the study of matter and thechanges it undergoes (another definition)

water, ammonia, sucrose, gold, oxygen

A mixture is a combination of two or more substances in which the substances retain their distinct identities.

1. Homogenous mixture – composition of the mixture is the same throughout.

2. Heterogeneous mixture – composition is not uniform throughout.

air, soft drink, milk, solder

cement, iron filings in sand

Physical means can be used to separate a mixture into its pure components.

magnetdistillation

An element is a substance that cannot be separated into simpler substances by chemical means.

• 115 elements have been identified

• 83 elements occur naturally on Earth

gold, aluminum, lead, oxygen, carbon

• 32 elements have been created by scientists

technetium, americium, seaborgium

These elements vary widely in their abundance, as shown in Figure 1.6.

Figure 1.6 Elements in percent by mass in (a) Earth's crust (including oceans and atmosphere) and (b) the human body.

Some of the more familiar elements are listed in Table 1.2, along with the chemical abbreviations—or chemical symbols—used to denote them.

All the known elements and their symbols are listed on the front inside cover of this text. The table in which the symbol for each element is enclosed in a box is called the periodic table.

The symbol for each element consists of one or two letters, with the first letter capitalized. These symbols are often derived from the English name for the element, but sometimes they are derived from a foreign name instead (last column in Table 1.2).

A compound is a substance composed of atoms of two or more elements chemically united in fixed proportions.

Compounds can only be separated into their pure components (elements) by chemical means.

Water (H2O) Glucose (C6H12O6)

Ammonia (NH3)

Most elements can interact with other elements to form compounds. Hydrogen gas, for example, burns in oxygen gas to form water.

Figure 1.10

Conversely, water can be decomposed into its component elements (hydrogen and oxygen) by passing an electrical current through it, as shown in Figure 1.7.

Figure 1.7 Water decomposes into its component elements, hydrogen and oxygen, when a direct electrical current is passed through it. The volume of hydrogen (on the right) is twice the volume of oxygen (on the left).

Pure water, regardless of its source, consists of 11% hydrogen and 89% oxygen by mass.

This macroscopic composition corresponds to the molecular composition, which consists of two hydrogen atoms combined with one oxygen atom.

As seen in Table 1.3, the properties of water bear no resemblance to the properties of its component elements.

Hydrogen, oxygen, and water are each unique substances.

Law of constant composition: A law that states that the elemental composition of a pure compound is always the same, regardless of its

source. This law is also known as law of definite proportions. It was first put forth by the French chemist Joseph Louis Proust in 1800s.

Each of the followings can be classified as a heterogeneous mixture, homogeneous mixture, compound, or element. How would you classify each?

1) Iced tea a) heterogeneous mixture b) homogeneous mixture c) compound d) element

2) Ethyl alcohol a) heterogeneous mixture b) homogeneous mixture c) compound d) element

3) Ozone a) compound b) homogeneous mixture c) heterogeneous mixture d) element

4) Air in the classroom a) heterogeneous mixture b) homogeneous mixture c) compound d) element

5) Table salt a) heterogeneous mixture b) homogeneous mixture c) compound d) element

6) A salt and sand mixturea) heterogeneous mixture b) homogeneous mixture c) compound d) element

1) b 2) c 3) a 4) b 5) c 6) a

1) Which of the following is not matter? 

a) elemental phosphorus b) light c) dust d) pizza

2) Which of the following is a pure substance? 

a) concrete b) nitrogen c) blue-cheese salad dressing d) air

4) Which of the following is not a state of matter?a) Gasb) Vacuumc) Solidd) Liquid

1) b 2) b 3) b 4) b

3) Passing an electric current through a certain substance produces oxygen and sulfur. This substance cannot be a(n)

a) Compoundb) Elementc) Mixtured) Pure substance

Three States of MatterMatter can exist in one of three states of matter: a gas, a liquid, or a solid.

A gas is highly compressible and will assume both the shape and the volume of its container.

A liquid is not compressible and will assume the shape but not the volume of its container.

A solid also is not compressible, and it has a fixed volume and shape of its own.

Some Characteristics of Gases, Liquids and Solids and the Microscopic Explanation for the Behavior

gas liquid solidassumes the shape and volume of its

container

particles can move past one another

assumes the shape of the part of the container

which it occupies

particles can move/slide past one another

retains a fixed volume and shape

rigid - particles locked into place

compressible

lots of free space between particles

not easily compressible

little free space between particles

not easily compressible

little free space between particles

flows easily

particles can move past one another

flows easily

particles can move/slide past one another

does not flow easily

rigid - particles cannot move/slide past one

another

Properties of MatterEvery substance has a unique set of properties (or characteristics) that allow us to recognize it and to distinguish it from other substances. For example, the properties listed in Table 1.3 allow us to distinguish hydrogen, oxygen, and water from one another.

The properties of matter can be categorized as physical properties or chemical properties.

Physical properties can be measured without changing the identity and composition of the substance. These properties include color, odor, density, melting point, boiling point, and hardness.

Chemical properties describe the way a substance may change or react to form other substances. A common chemical property is flammability, the ability of a substance to burn in the presence of oxygen.

Extensive properties of substances depend on the quantity of the sample and include measurements of mass and volume. Extensive properties relate to the amount of substance present.

Some properties—such as temperature, melting point, and density—do not depend on the amount of the sample (matter) being examined. These properties, called intensive properties, are particularly useful in chemistry because many can be used to identify substances.

Physical or Chemical?

A physical change does not alter the composition or identity of a substance.

A chemical change alters the composition or identity of the substance(s) involved.

ice meltingsugar dissolving

in water

hydrogen gas burns in oxygen gas to form water

Which of the following is a chemical process? a) dissolving sugar in water b) crushing of stone c) tarnishing of silver d) melting of lead

Which of the following is an intensive quantity? a) heat content of a substance b) mass of a substance c) density of a substance d) volume of a substance

Which one of the following is a physical process? a) the rusting of iron b) the explosion of nitroglycerine c) the baking of a potato d) the condensation of water vapor e) the formation of polyethylene from ethylene

c

c

d

Matter - anything that occupies space and has mass.

mass – measure of the quantity of matter

SI unit of mass is the kilogram (kg)

1 kg = 1000 g = 1 x 103 g

weight – force that gravity exerts on an object

weight = g x mass

on earth, g = 9.8 m/s2

on moon, g= 1.63 m/s2

A 60 kg bar will weigh

~600 N on earth

~100 N on moon

Table 1.2 SI Base Units

Base Quantity Name of Unit Symbol

Length meter m

Mass kilogram kg

Time second s

Current ampere A

Temperature kelvin K

Amount of substance mole mol

Luminous intensity candela cd

Table 1.3 Prefixes Used with SI Units

Prefix Symbol Meaning

Tera- T 1012

Giga- G 109

Mega- M 106

Kilo- k 103

Deci- d 10-1

Centi- c 10-2

Milli- m 10-3

Micro- 10-6

Nano- n 10-9

Pico- p 10-12

UnitEx. meter

Volume – SI derived unit for volume is cubic meter (m3)

1 cm3 = (1 x 10-2 m)3 = 1 x 10-6 m3

1 dm3 = (1 x 10-1 m)3 = 1 x 10-3 m3

1 L = 1000 mL = 1000 cm3 = 1 dm3

1 mL = 1 cm3

Density – SI derived unit for density is kg/m3

1 g/cm3 = 1 g/mL = 1000 kg/m3

density = mass

volume d = mV

A piece of platinum metal with a density of 21.5 g/cm3 has a volume of 4.49 cm3. What is its mass?

d = mV

m = d x V = 21.5 g/cm3 x 4.49 cm3 = 96.5 g

273 K = 0 0C 373 K = 100 0C

32 0F = 0 0C 212 0F = 100 0C

0F = x 0C + 3295

K = 0C + 273.15

0C = x (0F – 32)59

0 0C = 32 0F100 0C = 212 0F

Convert 172.9 0F to degrees Celsius.

0F = x 0C + 3295

0F – 32 = x 0C95

x (0F – 32) = 0C95

0C = x (0F – 32)95

0C = x (172.9 – 32) = 78.395

Scientific NotationThe number of atoms in 12 g of carbon:

602,200,000,000,000,000,000,000

6.022 x 1023

The mass of a single carbon atom in grams:

0.0000000000000000000000199

1.99 x 10-23

N x 10n

N is a number between 1 and 10

n is a positive or negative integer

Scientific Notation568.762

n > 0

568.762 = 5.68762 x 102

move decimal left

0.00000772

n < 0

0.00000772 = 7.72 x 10-6

move decimal right

Addition or Subtraction

1. Write each quantity with the same exponent n

2. Combine N1 and N2 3. The exponent, n, remains

the same

4.31 x 104 + 3.9 x 103 =

4.31 x 104 + 0.39 x 104 =

4.70 x 104

Scientific Notation

Multiplication

1. Multiply N1 and N2

2. Add exponents n1 and n2

(4.0 x 10-5) x (7.0 x 103) =(4.0 x 7.0) x (10-5+3) =

28 x 10-2 =2.8 x 10-1

Division

1. Divide N1 and N2

2. Subtract exponents n1 and n2

8.5 x 104 ÷ 5.0 x 109 =(8.5 ÷ 5.0) x 104-9 =

1.7 x 10-5

Significant Figures

0.00420 g 3 significant figures

• Any digit that is not zero is significant

1.234 kg 4 significant figures

• Zeros between nonzero digits are significant

606 m 3 significant figures

• Zeros to the left of the first nonzero digit are not significant

0.08 L 1 significant figure

• If a number is greater than 1, then all zeros to the right of the decimal point are significant

2.0 mg 2 significant figures

• If a number is less than 1, then only the zeros that are at the end and in the middle of the number are significant

The use of exponential notation eliminates the potential ambiguity of whether the zeros at the end of a number are significant

• When a number ends in zeros but contains no decimal point, the zeros may or may not be significant. 5000 (one, two, three, or four significant figures) 10,500 (three, four, or five significant figures)

1.03 x 104

1.030 x 104

1.0300 x 104

Three significant figures

Four significant figures

Five significant figures

How many significant figures are in each of the following measurements?

24 mL 2 significant figures

3001 g 4 significant figures

0.0320 m3 3 significant figures

6.4 x 104 molecules 2 significant figures

560 kg 2 or 3 significant figures

560. kg 3 significant figures

Significant Figures

Addition or SubtractionThe answer cannot have more digits to the right of the decimalpoint than any of the original numbers.

89.3321.1+

90.432 round off to 90.4

one significant figure after decimal point

3.70-2.91330.7867

two significant figures after decimal point

round off to 0.79

Significant Figures

Multiplication or Division

The number of significant figures in the result is set by the original number that has the smallest number of significant figures

4.51 x 3.6666 = 16.536366 = 16.5

3 sig figs round to3 sig figs

6.8 ÷ 112.04 = 0.0606926

2 sig figs round to2 sig figs

= 0.061

Accuracy – how close a measurement is to the true value

Precision – how close a set of measurements are to each other

accurate&

precise

precisebut

not accurate

not accurate&

not precise

1. Determine which unit conversion factor(s) are needed

2. Carry units through calculation

3. If all units cancel except for the desired unit(s), then the problem was solved correctly.

Dimensional Analysis

Given unit xDesired unit

Given unit= Desired unit

1 L = 1000 mL

How many mL are in 1.63 L?

1L

1000 mL1.63 L x = 1630 mL

1L1000 mL

1.63 L x = 0.001630L2

mL

We know that 1 inch is the same length as 2.54 centimeters. We’re told that the new start of the Indians basketball team is 64 cm tall and that he’s going to be the starting center. Based on height alone we’ll be able to tell if he’ll help the team but we Americans think in INCHES not CENTIMETERS so we need to convert units.

1 in

2.54 cm64 cm X

64

2.54in

Given unit xDesired unit

Given unit= Desired unit

Desired unit

Given unit

Remember

= 25.4 in

The speed of sound in air is about 343 m/s. What is this speed in miles per hour?

1 mi = 1609 m 1 min = 60 s 1 hour = 60 min

343ms

x1 mi

1609 m

60 s

1 minx

60 min

1 hourx = 767

mihour

meters to miles

seconds to hours

A car travels 28 mi per gallon of gasoline. How many kilometer per liter will it go?

1.0 km = 0.62137 mi or1.0 km

0.62137 mi

1.0 gal = 3.7854 L or 1.0 gal3.7854 L

Con

vers

ion

fact

ors

1.0 km

0.62137 mior

1.0 gal

3.7854 Lor

28migal

x1.0 km

0.62137 mi= 45

kmgal

45kmgal

1 gal

3.7854 Lx = 12 km

L

28migal

x1 km

0.62137 mi

1 gal

3.7854 Lx = 12 km

L

TWO steps

ONE step

Watch for significant figures. The real number is 11.9 km/L, however, here we have three sig. figures. We have started with a two sig. figure number (28). Thus, the final answer has to have two significant figures!

Step 1

Step 2