the study of chemistry.ppt

7/28/2019 The Study of Chemistry.ppt

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Oxygen

Carbon Dioxide

Ethylene glycol

Ethanol

Aspirin

Water


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Why Study Chemistry?

It provides an important understanding of our

world and how it works Improvement of health care

Conservation of natural resources

Protection of the environment

Increased food production Development of new materials

It is, by its very nature the central science

Astronomy, atmospheric science, biology, geology,

environmental science, medicine, physics, materialscience, and polymers

The language of chemistry is a universalscientific language


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How Do I Study Chemistry?

It takes lots of practice--homework, reviewing notes,reading the text.

It is different than some other disciplines MICHELANGELO Buonarroti, Italian painter, sculptor andarchitect (1475-1564). If a block of marble were at the frontof this room I suspect we would select Michelangelo to teach

us this art form.Antoine Lavoisier (1743-1794:guillotined) is called theFather of Modern Chemistry but he thinks waters formula isHO. He knows of about a dozen elements, nothing about

polymers, nuclear chemistry, ceramics, etc.

You must study differently for chemistry--study nearlyevery day. The best predictor of your final grade is yourgrade on the first exam.


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B. Classifications of Matter

States of Matter

a gas, a liquid, or a solid

states of matter differ in some of their simple

observable properties gases (vapors) have no fixed volume or shape. They

can be compressed to occupy a smaller volume or

allowed to expand to occupy a larger volume

liquids have a distinct volume independent of thecontainer that they occupy. They assume the shape

of the portion of the container they occupy

solids have a definite shape and a definite volume


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Pure Substances

Most forms of matter are not chemically pure

air

gasoline

Sidewalks

Pure substances have distinct properties and acomposition that does not vary from sample to sample

All substances are elements or compounds elements cannot be decomposed into simpler substances

carbon, helium, iron, oxygen, chlorine, etc.

compounds are composed of two or more elements

Water (H2O) is composed of two elements, hydrogen andoxygen

Mixtures are combinations of two or more substancesin which each substance retains its own chemicalidentity


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Atoms of an element Molecules of an element

Mixture of elements

and a compound

Molecules of a compound


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Some Common Elements and Their Symbols

Carbon C Aluminum Al Copper Cu (fromcuprum )

Fluorine F Barium Ba Iron Fe (fromferrum )

Hydrogen H Calcium Ca Lead Pb (fromplumbum )Iodine I Chlorine Cl Mercury Hg (from hydragyrum )

Nitrogen N Helium He Potassium K (fromkalium )

Oxygen O Magnesium Mg Silver Ag (fromargentum )

Phophorus P Platinum Pt Sodium Na (from natrium )

Sulfur S Silicon Si Tin Sn (fromstannum )

The symbol for each element consist of one or two letters, with the

first letter capitalized.

You will need to know the symbols and names for the first 100 elements


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Compounds

Most elements interact with other elements to formcompounds

Hydrogen burns in oxygen to form water (one O and two Hatoms)


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The observation that the elemental composition of apure compound is always the same is known as the lawof constant composition (law of definite proportions)

Mixtures

Most of the matter we encounter consists of mixtures ofdifferent substances

Each substance in a mixture retains its own chemicalidentity and properties

Mixture composition can vary

a cup of sweetened coffee. chocolate chip cookies. water foundin nature, rocks, wood, cement, steel, etc.

Some mixtures are uniform throughout Homogeneous mixtures or solutions

Some mixtures are not uniform throughout

Heterogeneous mixtures


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C. Properties of Matter

Every substance has a unique set ofproperties characteristics that allow us to recognize and

distinguish one substance from another

Properties of matter can categorized as either

physical orchemical Physical properties can be measured without

changing the identity and composition of thesubstance

Color, odor, density, melting point, boilingpoint, hardness, etc.

Chemical properties describe the way a substancemay change orreactto form other substances

A common chemical property is flammability


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Some properties, such as temperature, meltingpoint, and density, do not depend on the

amount of sample being examinedintensiveproperties.

used to identify substances

Some properties, such as mass and volume, dodepend on the amount of sample beingexaminedextensive properties.


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Physical and Chemical Changes

Duringphysical changes a substances changes

its physical appearance, but not its composition ice melting to become water

water evaporating to become steam

All state changes are physical changes

During chemical changes (chemical reactions) a

substances is changed into a chemically

different substance

propane burning to form carbon dioxide and water

scrambling an egg

a change in state will not revert the substance back

to its original form


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Separation of Mixtures

Mixtures can be separated into their constituent

components mixture components retain their own properties

Take advantage of the differences in the properties

Heterogeneous Mixtures

visual differences

magnetic differences

state differences

Homogeneous Mixtures

Boiling point difference

Polarity differences


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D. Units of Measurement

Many properties of matter are quantitative; thatit, they are associated with numbers

To say that the length of a pencil is 17.5 ismeaningless

The units used for scientific measurements are

those of the

Metric System


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1. SI Units

1960 - international agreement specifying a

particular choice of seven metric units forscientific measurements

SI = Systme International dUnits

SI Base Units

Physical Quantity Name of Unit Abbreviation

Mass Kilogram Kg

Length Meter m

Time Second sa

Temperature Kelvin K

Amount of substance Mole mol

Electric current Ampere A

Luminous intensity Candela cda

The abbreviation sec is frequently used


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Prefixes are used to indicate decimal factions ormultiples of various units

Exponential notation is used to avoid ambiguitywith regard to value certainty, see section 1.8.Learn these prefixes in Table 1.3.

Selected Prefixes Used in the Metric System

Prefix Abbreviation Meaning Example

Giga G 109 1 gigameter (Gm) = 1 X 10 9 m

Mega M 106 1 megameter (Mm) = 1 X 10 6 m

Kilo k 103 1 kilometer (km) = 1 X 10 3 m

Deci d 10-1 1 decimeter (dm) = 0.1 m = 1 X 10 -1 m

Centi c 10-2

1 centimeter (cm) = 0.01 m = 1 X 10-2

mMilli m 10-3 1 millimeter (mm) = 0.001 m = 1 X 10 -3 m

Micro a 10-6 1 micrometer ( m) = 1 X 10 -6 m

Nano n 10-9 1 nanometer (nm) = 1 X 10 -9 m

Pico p 10-12 1 picometer (pm) = 1 X 10 -12 m

Femto f 10-15 1 femtometer (fm) = 1 X 10 -15 m

aThis is the Greek letter mu (pronounced "mew").


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2. Length and Mass

SI base unit oflength is the meter(m)

1 m = 100 cm = 39.37 inches (slightly longerthan a yard)

Mass is a measure of the amount of material inan object.

Mass is different from weight, which dependsupon gravity

SI base unit ofmass is the kilogram (kg)

This base unit is unusual because it uses a prefix,kilo-, instead of the wordgram alone.

Other units of mass are obtained by adding prefixesto the wordgram


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3. Temperature

We sense temperature as a measure of hotness

and coldnessTemperature determines the direction of heat

flow

Heat always flows spontaneously from a substance

at higher temperature to one at lower temperature.The temperature scales commonly employed in

scientific studies are the Celsius and Kelvinscales

The Celsius scale, the everyday scale of temperaturein most countries throughout the world, wasoriginally based on the assignment of 0C to thefreezing poing of water and 100C to its boiling

point at sea level.


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The Kelvin Scale is the SI temperature scale and theSI unit of temperature is the Kelvin (K).

Zero on this scale is - 273.15C, once believed to bethe lowest attainable temperature. Because of this,0K is known as Absolute Zero.

Both the Celsius and Kelvin scales have equal-sizedunitsthat is, a kelvin is the same size as a degreeCelsius.

K = C + 273.15

The freezing point of water, 0C, is 273.15 K

Notice that the degree symbol () is not usedwith temperatures on the Kelvin scale.


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The common temperature scale in the US is theFahrenheit scale

Freezing point of water = 32F

Boiling point of water = 212F

C = 5/9 (F - 32) or F = 9/5 (C) + 32


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4. Volume

The volume of a cube is given by its length

cubed, (length)3

The basic SI unit of volume is the cubic meter

Another common unitof volume is the liter(L),

which equals a cubicdecimeter, dm3.

It is slightly larger than aquart

There are 1000 milliliters (mL)in a liter

Each milliliter is the same volume as acubic centimeter


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Devices Used Most Frequently in Chemistry to Measure Volume


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5. Density

Widely used to characterize substances

Amount of mass in a unit volume of thesubstance

Densitymass

volume=

Densities of solids and liquids are commonly

expressed in grams per cubic centimeter (g/cm3)

or grams per milliliter (g/mL)

The density of water is 1.00 g/ml

Most substances change volume when heated or

cooledDensities are temperature dependent

Assume 25C unless otherwise noted


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Densities of Some Selected Substances at 25C

Substance Density (g/cm3)

Air 0.001

Balsa wood 0.16

Ethanol 0.79

Water 1.00

Ethylene glycol 1.09

Table sugar 1.59

Table salt

Iron 7.9Gold 19.32


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E. Uncertainty in Measurement

There are two kinds of numbers in scientific work:Exact numbers (those whose values are known

exactly)

12 eggs in a dozen, exactly 1000 g in akilogram, and exactly 2.54 cm in an inch

and inexact numbers (those whose values have

some uncertainty)

numbers obtained by measurement

Uncertainties always exist for in measured quantities


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1. Precision and Accuracy

Precision is a measure of how closely

individual measurements agree with oneanother

Accuracy refers to how closely individual

measurements agree with the correct, or true

value.


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2. Significant Figures

Precision of a measured number is indicated

using the concept ofsignificant figures. Those digits in a measured number (or result of a

calculation with measured numbers) that include all

certain digits plus a final one have some uncertainty.

Three measurements (9.12, 9.11, and 9.13 cm)

Avg = 9.12 First two digits (9.1) are certain,

the next digit is estimated, so it has some

uncertainty.


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The greater the number of significant figures,

the greater the certainty implied for the

measurementIn any measurement that is properly reported,

all nonzero digits are significant. Zeros can be

used either as part of the measured value or

merely to locate the decimal point.

Zeros between nonzero digits are always significant

Zeros starting a number are never significant

Zeros ending a number to the right of the decimalpoint are always significant

Zeros ending a number to the left of the decimal

point may or may not be significant

Exponential notation is the solution


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Significant Figures inCalculations

Suppose that 0.0634 g of a compound

will dissolve in 25.31 g of water. How

many grams will dissolve in 100 g ofwater?

10,300

counted by ones = 5 significant figures = 1.0300 x 104

counted by tens = 4 significant figures = 1.030 x 104

counted by 100s = 3 significant figures = 1.03 x 104


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Significant Figure Calculation Rules

Multiplication and Division. When multiplying or dividing measuredquantities, give as many significant figures in the answer as there are

in the measurement with the least number of significant figures.

103.0 x 0.0634 = 6.5302 6.53

2.564 4.522 x 10-2

If the leftmost digit to be dropped is 5, round the last significantfigure up, otherwise simply drop the nonsignificant digits.


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Significant Figure Calculation Rules

Addition and Subtraction. When adding or subtracting measuredquantities, give the same number of decimal places in the answer as

there are in the measurement with the least number of significant

figures.

If the leftmost digit to be dropped is 5, round the last significantfigure up, otherwise simply drop the nonsignificant digits.

10.234 + 0.66 = 16.894 16.89

9.56 = 4.38


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II. Dimensional Analysis

A. This process is called

1. Dimensional analysis (we will use this name)2. Factor-label method, Unit conversion method,

or the Unit Factor Method

Dimensional analysis is a problem solving aid used tohelp ensure that the solutions to problems yield the

proper units.

It provides a systematic way of solving any numericalproblems and of checking solutions for possible errors.

The key to using dimensional analysis is the correct useof conversion factors to change one unit into another.

This method will work for many chemical calculations.When it is not convenient you must still cancel the units

to be certain your answer has the proper dimensions.


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1. A conversion factor is a fraction whose numerator

and denominator are the same quantity expressed

in different units.

2.54 cm and 1 in. are the same length

2.54 cm = 1 in.

2. Two important mathematical realities

Doing the same thing to both sides of an

equation does not change the relationshipMultiplying one does not change the anything

2.54 cm

2.54 cm

1 in.

2.54 cm

== 1 =2.54 cm

1 in.

1 in.

1 in.

=


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3. Since conversion factors are the number one in a

different form, multiplying a measurement and its

units by any number of conversion factors changesthe value and the units but not the reality of the

measurement itself.

How many seconds in a century?

x sec = 1 century 100 years

1 centuryx

365 days

1 yearx

24 hours

1 dayx

60 minutes

1 hourx

60 seconds

1 minutex

1 century = 100 years1 year = 365 days1 day = 24 hours

1 hour = 60 minutes1 minute = 60 seconds

x sec = 3,153,600,000 (3.1536 x 109) sec


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B. Conversion Factors:

Constructed from any two terms that are equal to

each other. If two quantities are equal and if one isthen divided by the other, the quotient equals one

and it is called a Unit Factor or a Conversion Factor.

Remember: any quantity can be multiplied by one

without changing the result.

Examples of Conversion Factors, Memorize these.

a. 1.00 inch = 2.54 cm Length

b. 454 g = 1.00 lb Mass

c. 1.00 L = 1.057 qt Volume

d. 1.00 mL = 1.00 cm3 = 1.00 cc

(learn these first four conversions):

e. 1.00 mol Mg = 24.3 g of Mg

f. Many others that you will learn.


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Volume, like other concepts that will be encountered

throughout the semester, requires the use of

relationships that necessitate the raising ofnumbers to a power, cubing in this specific case

It is imperative to remember to raise both thenumber and the units to the appropriate power

and not just the units

1 in = 2.54 cm 1 in3 2.54 cm3

1 in3 = (1 in)3 = (2.54 cm)3 = 16.39 cm3


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C. Recipe for Dimensional Analysis

1. On the far right, write down the units of the answer.

2. Analyze the information given or known (the units) to

select the proper starting quantity. This information may be

from the problem, the periodic chart, some physical law, or

something you learned.3. Analyze the dimensions (units) of the answer and the

dimensions (units) of the starting quantity to determine the

proper unit factors (conversion factors) to convert the units

given into the units of the answer.

4. This may require several unit factors.

5. Cancel the units and do the numerical calculation.


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Examples:

1. How many inches in 2.57 ft? DO

ANS:

2. How many nm in 3.72 yds? DO

ANS:


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3. A major contributor to global environmental pollution is from coal

burning power plants. Carbon dioxide, a greenhouse gas, is the

major product and all coal contains various amounts of sulfur that

eventually contributes to acid rain. A typical coal burning powerplant burns 2500 tons of coal per day, with a sulfur content of 3%,

and the density of solid bituminous coal is 1346 kg/m3 (solid

anthracite coal has a density of 1506 kg/m3).

a. What volume, in cubit feet, of bituminous coal is burned by atypical coal burning power plant each day?

ANS:


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4. Determine the volume in ft3 of a piece of Pb that has a mass of 13.4

kg, if the density is 11.2 g/cm3. DO

ANS:

5. A gallon of milk weighs 8.00 lbs.

a. What is the mass of one pint in grams? DO

ANS:

b. What is the density of milk in g/mL? DO

ANS:

D l I b ll/D S


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Douglas Isbell/Don SavageHeadquarters, Washington, DC Nov. 10, 1999(Phone: 202/358-1547) Embargoed until 2 p.m. ESTRELEASE: 99-134

MARS CLIMATE ORBITER FAILURE BOARD RELEASES REPORT,NUMEROUS NASA ACTIONS UNDERWAY IN RESPONSE

Wide-ranging managerial and technical actions are underway at NASA's JetPropulsion Laboratory, Pasadena, CA, in response to the loss of the $125 million MarsClimate Orbiter and the initial findings of the mission failure investigation board, whose

first report was released today.

"The 'root cause' of the loss of the spacecraft was the failed translation ofEnglish units into metric units in a segment of ground-based, navigation-relatedmission software, as NASA has previously announced," said ArthurStephenson, chairman of the Mars Climate Orbiter Mission FailureInvestigation Board. "The failure review board has identified other significantfactors that allowed this error to be born, and then let it linger and propagate tothe point where it resulted in a major error in our understanding of thespacecraft's path as it approached Mars.

WEB: http://mars.jpl.nasa.gov/msp98/news/mco991110.html

the study of chemistry.ppt

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