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Transcript of Mec chapter 1
Chapter 1
Chemistry: Methods and Measurement
Deniston Topping Caret
7th Edition
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1.1 The Discovery Process
• Chemistry - The study of matter…
– Matter - Anything that has mass and occupies space• A table• A piece paper
– What about air? • Yes, it is matter
1.1
Th
e D
isco
very
Pro
cess
Chemistry:• the study of matter• its chemical and physical properties• the chemical and physical changes it
undergoes• the energy changes that accompany
those processes
• Energy - the ability to do work to accomplish some change
1.1
Th
e D
isco
very
Pro
cess THE SCIENTIFIC METHOD
• The scientific method - a systematic approach to the discovery of new information
Characteristics of the scientific process
1. Observation
2. Formulation of a question
3. Pattern recognition
4. Developing theories
5. Experimentation
6. Summarizing information
1.1
Th
e D
isco
very
Pro
cess
Models in Chemistry
• To aid in understanding of a chemical unit or system– a model is often used– good models are based on
everyday experience
• Ball and stick methane model– color code balls– sticks show attractive forces
holding atoms together
1.1
Th
e D
isco
very
Pro
cess
1.2 Matter and Properties
• Properties - characteristics of matter– chemical vs. physical
• Three states of matter1. gas - particles widely separated, no definite
shape or volume solid
2. liquid - particles closer together, definite volume but no definite shape
3. solid - particles are very close together, define shape and definite volume
Three States of Water
(a) Solid (b) Liquid (c) Gas
Comparison of the Three Physical States
1.2
Mat
ter
and
Pro
pert
ies
1.2
Mat
ter
and
Pro
pert
ies • Physical property - is observed
without changing the composition or identity of a substance
• Physical change - produces a recognizable difference in the appearance of a substance without causing any change in its composition or identity- conversion from one physical state to
another
- melting an ice cube
Separation by Physical Properties
Magnetic iron is separated from other nonmagnetic substances, such as sand. This property is used as a large-scale process in the recycling industry.
1.2
Mat
ter
and
Pro
pert
ies
• Chemical property - result in a change in composition and can be observed only through a chemical reaction
• Chemical reaction (chemical change) - a process of rearranging, removing, replacing, or adding atoms to produce new substances
hydrogen + oxygen water
reactants products
1.2
Mat
ter
and
Pro
pert
ies Classify the following as either a
chemical or physical property:
a. Color
b. Flammability
c. Hardness
d. Odor
e. Taste
1.2
Mat
ter
and
Pro
pert
ies Classify the following as either a
chemical or physical change:
a. Boiling water becomes steam
b. Butter turns rancid
c. Burning of wood
d. Mountain snow pack melting in spring
e. Decay of leaves in winter
• Intensive properties - a property of matter that is independent of the quantity of the substance- Density
- Specific gravity
• Extensive properties - a property of matter that depends on the quantity of the substance- Mass
- Volume1.2
Mat
ter
and
Pro
pert
ies
1.2
Mat
ter
and
Pro
pert
ies
• Pure substance - a substance that has only one component
• Mixture - a combination of two or more pure substances in which each substance retains its own identity, not undergoing a chemical reaction
Classification of Matter
1.2
Mat
ter
and
Pro
pert
ies
• Element - a pure substance that cannot be changed into a simpler form of matter by any chemical reaction
• Compound - a substance resulting from the combination of two or more elements in a definite, reproducible way, in a fixed ratio
Classification of Matter
1.2
Mat
ter
and
Pro
pert
ies
• Mixture - a combination of two or more pure substances in which each substance retains its own identity
• Homogeneous - uniform composition, particles well mixed, thoroughly intermingled
• Heterogeneous – nonuniform composition, random placement
Classification of Matter
Classes of Matter1.
2 M
atte
r an
d P
rope
rtie
s
1.3 Measurement in ChemistryData, Results, and Units• Data - each piece is an individual result of a single
measurement or observation– mass of a sample
– temperature of a solution
• Results - the outcome of the experiment• Data and results may be identical, however usually
related data are combined to generate a result• Units - the basic quantity of mass, volume or
whatever quantity is being measured– A measurement is useless without its units
English and Metric Units
• English system - a collection of functionally unrelated units – Difficult to convert from one unit to
another – 1 foot = 12 inches = 0.33 yard = 1/5280 miles
• Metric System - composed of a set of units that are related to each other decimally, systematic – Units relate by powers of tens– 1 meter = 10 decimeters = 100 centimeters = 1000
millimeters
1.3
Mea
sure
men
t in
C
hem
istr
y
1.3
Mea
sure
men
t in
C
hem
istr
yBasic Units of the Metric System
Mass gram gLength meter mVolume liter L
• Basic units are the units of a quantity without any metric prefix
1.3
Mea
sure
men
t in
C
hem
istr
y
1.3
Mea
sure
men
t in
C
hem
istr
yUNIT CONVERSION
• You must be able to convert between units
- within the metric system
- between the English system and metric system
• The method used for conversion is called the Factor-Label Method or Dimensional Analysis
!!!!!!!!!!! VERY IMPORTANT !!!!!!!!!!!
1.3
Mea
sure
men
t in
C
hem
istr
y• Let your units do the work for you by
simply memorizing connections between units.– For example: How many donuts are in
one dozen?
– We say: “Twelve donuts are in a dozen.”– Or: 12 donuts = 1 dozen donuts
• What does any number divided by itself equal?
• ONE! 1 dozen 1
donuts 12
1.3
Mea
sure
men
t in
C
hem
istr
y1
dozen 1
donuts 12
• This fraction is called a unit factor
• What does any number times one equal?
• That number
• Multiplication by a unit factor does not change the amount – only the unit
• We use these two mathematical facts to use the factor label method– a number divided by itself = 1– any number times one gives that number
back
• Example: How many donuts are in 3.5 dozen?
• You can probably do this in your head but try it using the Factor-Label Method.1.
3 M
easu
rem
ent
in
Ch
emis
try
1.3
Mea
sure
men
t in
C
hem
istr
yStart with the given information...
3.5 dozen
Then set up your unit factor...
dozen 1
donuts 12
See that the units cancel...
Then multiply and divide all numbers...
= 42 donuts
1.3
Mea
sure
men
t in
C
hem
istr
yCommon English System Units
• Convert 12 gallons to units of quarts
1.3
Mea
sure
men
t in
C
hem
istr
yIntersystem Conversion Units
• Convert 4.00 ounces to kilograms
1.3
Mea
sure
men
t in
C
hem
istr
y 1. Convert 5.5 inches to millimeters
2. Convert 50.0 milliliters to pints
3. Convert 1.8 in2 to cm2
1.4 Significant Figures and Scientific Notation
• Information-bearing digits or figures in a number are significant figures
• The measuring devise used determines the number of significant figures a measurement has
• The amount of uncertainty associated with a measurement is indicated by the number of digits or figures used to represent the information
1.4
Sig
nif
ican
t F
igu
res
and
Sci
enti
fic
Not
atio
n
Significant figures - all digits in a number representing data or results that are known with certainty plus one uncertain digit
1.4
Sig
nif
ican
t F
igu
res
and
Sci
enti
fic
Not
atio
n Recognition of Significant Figures
• All nonzero digits are significant
• 7.314 has four significant digits
• The number of significant digits is independent of the position of the decimal point
• 73.14 also has four significant digits
• Zeros located between nonzero digits are significant
• 60.052 has five significant digits
1.4
Sig
nif
ican
t F
igu
res
and
Sci
enti
fic
Not
atio
nUse of Zeros in Significant
Figures• Zeros at the end of a number (trailing zeros) are
significant if the number contains a decimal point.
• 4.70 has three significant digits
• Trailing zeros are insignificant if the number does not contain a decimal point.
• 100 has one significant digit; 100. has three
• Zeros to the left of the first nonzero integer are not significant.
• 0.0032 has two significant digits
1.4
Sig
nif
ican
t F
igu
res
and
Sci
enti
fic
Not
atio
n
How many significant figures are in the following?
1. 3.400
2. 3004
3. 300.
4. 0.003040
1.4
Sig
nif
ican
t F
igu
res
and
Sci
enti
fic
Not
atio
n Scientific Notation
• Used to express very large or very small numbers easily and with the correct number of significant figures
• Represents a number as a power of ten
• Example:
4,300 = 4.3 x 1,000 = 4.3 x 103
• To convert a number greater than 1 to scientific notation, the original decimal point is moved x places to the left, and the resulting number is multiplied by 10x
• The exponent x is a positive number equal to the number of places the decimal point moved
5340 = 5.34 x 104
• What if you want to show the above number has four significant figures?
= 5.340 x 104
1.4
Sig
nif
ican
t F
igu
res
and
Sci
enti
fic
Not
atio
n
• To convert a number less than 1 to scientific notation, the original decimal point is moved x places to the right, and the resulting number is multiplied by 10-x
• The exponent x is a negative number equal to the number of places the decimal point moved
0.0534 = 5.34 x 10-2
1.4
Sig
nif
ican
t F
igu
res
and
Sci
enti
fic
Not
atio
n
Types of Uncertainty
• Error - the difference between the true value and our estimation
– Random
– Systematic
• Accuracy - the degree of agreement between the true value and the measured value
• Precision - a measure of the agreement of replicate measurements1.
4 S
ign
ific
ant
Fig
ure
s an
d S
cien
tifi
c N
otat
ion
1.4
Sig
nif
ican
t F
igu
res
and
Sci
enti
fic
Not
atio
n
correct answer 152.83 liters
Significant Figures in Calculation of Results
Rules for Addition and Subtraction
• The result in a calculation cannot have greater significance than any of the quantities that produced the result
• Consider:
37.68 liters 6.71862 liters
108.428 liters 152.82662 liters
1.4
Sig
nif
ican
t F
igu
res
and
Sci
enti
fic
Not
atio
n
)calculator(on 109688692.210255.2
)94.15(102.4 84
3
Which number has the fewest significant figures? 4.2 x 103 has only 2
The answer is therefore, 3.0 x 10-8
Rules for Multiplication and Division
• The answer can be no more precise than the least precise number from which the answer is derived
• The least precise number is the one with the fewest significant figures
1.4
Sig
nif
ican
t F
igu
res
and
Sci
enti
fic
Not
atio
n Exact and Inexact Numbers
• Inexact numbers have uncertainty by definition
• Exact numbers are a consequence of counting
• A set of counted items (beakers on a shelf) has no uncertainty
• Exact numbers by definition have an infinite number of significant figures
1.4
Sig
nif
ican
t F
igu
res
and
Sci
enti
fic
Not
atio
n
=3.35 x 104
Rules for Rounding Off Numbers
• When the number to be dropped is less than 5 the preceding number is not changed
• When the number to be dropped is 5 or larger, the preceding number is increased by one unit
• Round the following number to 3 significant figures: 3.34966 x 104
How Many Significant Figures?
Round off each number to 3 significant figures:
1. 61.40
2. 6.171
3. 0.066494
1.4
Sig
nif
ican
t F
igu
res
and
Sci
enti
fic
Not
atio
n
1.5 Experimental Quantities
• Mass - the quantity of matter in an object– not synonymous with weight– standard unit is the gram
• Weight = mass x acceleration due to gravity
• Mass must be measured on a balance (not a scale)
1.5
Exp
erim
enta
l Qu
anti
ties
• Units should be chosen to suit the quantity described – A dump truck is measured in tons– A person is measured in kg or pounds– A paperclip is measured in g or ounces– An atom?
• For atoms, we use the atomic mass unit (amu)– 1 amu = 1.661 x 10-24 g
1.5
Exp
erim
enta
l Qu
anti
ties
• Length - the distance between two points– standard unit is the meter– long distances are measured in km– distances between atoms are measured in nm,
1 nm = 10-9 m
• Volume - the space occupied by an object– standard unit is the liter– the liter is the volume occupied by 1000
grams of water at 4 oC– 1 mL = 1/1000 L = 1 cm3
1.5
Exp
erim
enta
l Qu
anti
ties
The milliliter (mL) and the cubic centimeter (cm3) are equivalent
1.5
Exp
erim
enta
l Qu
anti
ties • Time
- metric unit is the second
• Temperature - the degree of “hotness” of an object
1.5
Exp
erim
enta
l Qu
anti
ties
1.8
32-FC
oo
32C)(1.8F oo
1. Convert 75oC to oF
2. Convert -10oF to oC
1. Ans. 167 oF 2. Ans. -23oC
Conversions Between Fahrenheit and Celsius
1.5
Exp
erim
enta
l Qu
anti
ties
K = oC + 273
Kelvin Temperature Scale
• The Kelvin scale is another temperature scale.
• It is of particular importance because it is directly related to molecular motion.
• As molecular speed increases, the Kelvin temperature proportionately increases.
1.5
Exp
erim
enta
l Qu
anti
ties
• Energy - the ability to do work
• kinetic energy - the energy of motion
• potential energy - the energy of position (stored energy)
• Energy is also categorized by form:• light• heat• electrical• mechanical• chemical
Energy
1.5
Exp
erim
enta
l Qu
anti
ties
Characteristics of Energy
• Energy cannot be created or destroyed
• Energy may be converted from one form to another
• Energy conversion always occurs with less than 100% efficiency
• All chemical reactions involve either a “gain” or “loss” of energy
1.5
Exp
erim
enta
l Qu
anti
ties Units of Energy
• Basic Units:• calorie or joule• 1 calorie (cal) = 4.184 joules (J)
• A kilocalorie (kcal) also known as the large Calorie. This is the same Calorie as food Calories.
• 1 kcal = 1 Calorie = 1000 calories
• 1 calorie = the amount of heat energy required to increase the temperature of 1 gram of water 1oC.
1.5
Exp
erim
enta
l Qu
anti
ties
V
md
volume
mass
Density and Specific Gravity
• Density – the ratio of mass to volume– an extensive property– use to characterize a substance as
each substance has a unique density
– Units for density include:• g/mL• g/cm3
• g/cc
1.5
Exp
erim
enta
l Qu
anti
ties
liquid mercury
brass nut
water
cork
Calculating the Density of a Solid
• 2.00 cm3 of aluminum are found to weigh 5.40g. Calculate the density of aluminum in units of g/cm3.– Use the formula– Substitute our values
5.40 g
2.00 cm3
= 2.70 g / cm3
1.5
Exp
erim
enta
l Qu
anti
ties
V
md
volume
mass
1.5
Exp
erim
enta
l Qu
anti
ties
Air has a density of 0.0013 g/mL. What is the mass of 6.0-L sample of air?
Calculate the mass in grams of 10.0 mL if mercury (Hg) if the density of Hg is 13.6 g/mL.
Calculate the volume in milliliters, of a liquid that has a density of 1.20 g/mL and a mass of 5.00 grams.
1.5
Exp
erim
enta
l Qu
anti
ties
(g/mL) water ofdensity
(g/mL)object ofdensity gravity specific
Specific Gravity
• Values of density are often related to a standard
• Specific gravity - the ratio of the density of the object in question to the density of pure water at 4oC
• Specific gravity is a unitless term because the 2 units cancel
• Often the health industry uses specific gravity to test urine and blood samples