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Jeffrey MackJeffrey MackCalifornia State University, California State University,
SacramentoSacramento
2
• HypothesisHypothesis: A tentative explanation or prediction based on experimental observations.
• LawLaw: A concise verbal or mathematical statement of a behavior or a relation that seems always to be the same under the same conditions.
• TheoryTheory: a well-tested, unifying principle that explains a body of facts and the laws based on them. It is capable of suggesting new hypotheses that can be tested experimentally.
Chemistry and Its MethodsChemistry and Its Methods
3
• Experimental results should be reproducible.• Furthermore, these results should be
reported in the scientific literature in sufficient detail that they can be used or reproduced by others.
• Conclusions should be reasonable and unbiased.
• Credit should be given where it is due.
Chemistry and Its MethodsChemistry and Its Methods
4
• No numbers involved• Color, appearance, statements like “large” or
“small:• Stating that something is hot or cold without
specifying a temperature.• Identifying something by smell• No measurements
Qualitative ObservationsQualitative Observations
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• A quantity or attribute that is measureable is A quantity or attribute that is measureable is specified.specified.
• Numbers with units are expressed from Numbers with units are expressed from measurements.measurements.
• Dimensions are given such as mass, time, Dimensions are given such as mass, time, distance, volume, density, temperature, color distance, volume, density, temperature, color specified as a wavelength etc...specified as a wavelength etc...
Qualitative ObservationsQualitative Observations
6Classifying Matter: States of MatterClassifying Matter: States of Matter
7Classifying Matter: States of MatterClassifying Matter: States of Matter
• In solids these particles are packed closely together, usually in a regular array. The particles vibrate back and forth about their average positions, but seldom does a particle in a solid squeeze past its immediate neighbors to come into contact with a new set of particles.
• The atoms or molecules of liquids are arranged randomly rather than in the regular patterns found in solids. Liquids and gases are fluid because the particles are not confined to specific locations and can move past one another.
• Under normal conditions, the particles in a gas are far apart. Gas molecules move extremely rapidly and are not constrained by their neighbors. The molecules of a gas fly about, colliding with one another and with the container walls. This random motion allows gas molecules to fill their container, so the volume of the gas sample is the volume of the container.
8
• SOLIDSSOLIDS — have rigid shape, fixed volume. External shape may reflect the atomic and molecular arrangement.–Reasonably well understood.
• LIQUIDSLIQUIDS — have no fixed shape and may not fill a container completely. –Structure not well understood.
• GASESGASES — expand to fill their container completely. –Well defined theoretical understanding.
States of MatterStates of Matter
9Classifying MatterClassifying Matter
10
Mixtures: Homogeneous and Heterogeneous• A homogeneoushomogeneous mixture consists of two or
more substances in the same phase. No amount of optical magnification will reveal a homogeneous mixture to have different properties in different regions.
• A heterogeneousheterogeneous mixture does not have uniform composition. Its components are easily visually distinguishable.
• When separated, the components of both types of mixtures yields pure substancespure substances.
Classifying MatterClassifying Matter
11Classifying MatterClassifying Matter
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Pure SubstancesPure Substances• A pure substance has well defined physical
and chemical properties.• Pure substances can be classified as
elementselements or compoundscompounds.• Compounds can be further reduced into two
or more elements.• Elements consist of only one type of atom.
They cannot be decomposed or further simplified by ordinary means.
Classifying MatterClassifying Matter
13
Chemical symbols allow us to connect…
What we observe…
To what we can’t see!
Matter and its RepresentationMatter and its Representation
14
In chemistry we use chemical formulas and symbols to represent matter.
Why?Why?
We are “macroscopic”: large in size on the order of 100’s of cm.
Atoms and molecules are “microscopic”: on the order of 10-12 cm
The Representation of MatterThe Representation of Matter
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• The elements are recorded on the PERIODIC TABLEPERIODIC TABLE• There are 117 recorded elements at this time.• The Periodic table will be discussed further in chapter 2.
ElementsElements
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Chemical compounds are composed of two or more atoms.
Chemical CompoundsChemical Compounds
17Chemical CompoundsChemical Compounds
Molecule:
Ammonia (NH3)
Ionic Compound
Iron pyrite (FeS2)
18Chemical CompoundsChemical Compounds
• All Compounds are made up of molecules or ions.
• A molecule is the is the smallest unit of a compound that retains its chemical characteristics.
• Ionic compounds are described by a “formula unit”.
• Molecules are described by a “molecular formula”.
19Molecular FormulaMolecular Formula
• A moleculemolecule is the smallest unit of a compound that retains the chemical characteristics of the compound.
• Composition of molecules is given by a molecular formulamolecular formula.
H2O C8H10N4O2 - caffeine
20Physical PropertiesPhysical Properties
Some physical properties:− Color− State (s, g or liq)− Melting and Boiling point− Density (mass/unit volume)
Extensive propertiesExtensive properties (mass) depend upon the amount of substance.Intensive propertiesIntensive properties (density) do not.
21
Physical properties are a function of intermolecular forces.
O
H H
Water (18 g/mol)liquid at 25oC
Methane (16 g/mol)gas at 25oC
C
H
HHH
Physical PropertiesPhysical Properties
• Water molecules are attracted to one another by “hydrogen bonds”. • Methane molecules only exhibit week “London Forces”.
22
Physical properties are affected by temperature (molecular motion).
The density of water is seen to change with temperature.
Physical PropertiesPhysical Properties
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Mixtures may be separated by physical properties:
Physical PropertiesPhysical Properties
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• Chemical properties are really chemical changes.• The chemical properties of elements and
compounds are related to periodic trends and molecular structure.
Chemical PropertiesChemical Properties
25Chemical PropertiesChemical Properties
A chemical property indicates whether and sometimes how readily a material undergoes a chemical change with another material.
For example, a chemical property of hydrogen gas is that it reacts vigorously with oxygen gas.
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Chemists are interested in the nature of matter and how this is related to its atoms and molecules.
GoldGold MercuryMercury
The Nature of MatterThe Nature of Matter
A ChemistA Chemist’’s View s View of Waterof Water
H2O (gas, liquid, solid)
MacroscopicMacroscopic
SymbolicSymbolicParticulateParticulate
2 H2(g) + O2 (g) 2 H2O(g)
28
Energy can be classified as KineticKinetic or PotentialPotential.• Kinetic energyKinetic energy is energy associated with motion such
as:
• The motion at the particulate level (thermal energy).
• The motion of macroscopic objects like a thrown baseball, falling water.
• The movement of electrons in a conductor (electrical energy).
• Wave motion, transverse (water) and compression (acoustic).
Matter consists of atoms and molecules in motion.
Energy: Some Basic PrinciplesEnergy: Some Basic Principles
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Potential energyPotential energy results from an object’s position:• Gravitational: An object held at a height,
waterfalls. • Energy stored in an extended spring.• Energy stored in molecules (chemical energy,
food) • The energy associated with charged or partially
charged particles (electrostatic energy)• Nuclear energy (fission, fusion).
Energy: Some Basic PrinciplesEnergy: Some Basic Principles
Jeffrey MackJeffrey MackCalifornia State University, California State University,
SacramentoSacramento
31
"In physical science the first essential step in the direction of learning any subject is to find principles of numerical reckoning and practicable methods for measuring some quality connected with it.
I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the state of Science, whatever the matter may be."
Lord Kelvin, "Electrical Units of Measurement", 1883-05-03
The Tools of Quantitative ChemistryThe Tools of Quantitative Chemistry
32Note About Math & ChemistryNote About Math & Chemistry
Numbers and mathematics are an inherent and unavoidable part of general chemistry. Students must possess secondary algebra skills and the ability to recognize orders of magnitude quickly with respect to numerical information to assure success in this course.
The material presented in this chapter is considered to be prerequisite to this course.
33
Science predominantly uses the “SI” (System International) system of units, more commonly known as the “Metric System”.
Units of MeasureUnits of Measure
34
The base units are modified by a series of prefixes which you will need to memorize.
Units of MeasureUnits of Measure
35
Temperature is measured in the CelsiusCelsius an the KelvinKelvin temperature scale.
Temperature UnitsTemperature Units
36
1KT(K) T C 273.15 C
1 C
1K25.0 C 273.15 C 298.2K
1 C
Temperature ConversionTemperature Conversion
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The base unit of length in the metric system is the metermeter..
Depending on the object measured, the meter is scaled accordingly.
Length, Volume, and MassLength, Volume, and Mass
38
Unit conversions: How many picometers are there in 25.4 nm? How many yards?
Length, Volume, and MassLength, Volume, and Mass
124
9
2
nm m pm
1m 1 10 pm25.4nm 2.54 10 pm
1 10 nm 1m
m cm in ft yd
10 cm 1in 1ft 1yd25.4m 27.8 yards
1m 2.54cm 12in 3ft
39
The base unit of volume in the metric system is the literliter. .
1 L = 103 mL 1 mL=1 cm3 1 cm3 = 1 mL
Length, Volume, and MassLength, Volume, and Mass
3
3 34 3
L mL cm
10 mL 1cm25.4 L 2.54 10 cm
1 L 1 mL
40
The base unit of volume in the metric system is the gramgram.
1kg = 103g
Length, Volume, and MassLength, Volume, and Mass
119 3
ng g kg
1g 1kg25.4ng 2.54 10 g
1 10 ng 1 10 g
41
EnergyEnergy is confined as the capacity to do work.The SI unite for energy is the joulejoule (J).
Energy is also measured in calories (cal)1 cal = 4.184J
A kcal (kilocalorie) is often written as Cal. 1 Cal =103 cal
Energy UnitsEnergy Units
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The precisionprecision of a measurement indicates how well several determinations of the same quantity agree.
Making Measurements: PrecisionMaking Measurements: Precision
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AccuracyAccuracy is the agreement of a measurement with the accepted value of the quantity.
Accuracy is often reflected by Experimental Experimental errorerror.
Making Measurements: AccuracyMaking Measurements: Accuracy
44
The Standard Deviation Standard Deviation of a series of measurements is equal to the square root of the sum of the squares of the deviations for each measurement from the average divided by one less than the number of measurements (n).
Measurements are often reported to the standard deviation to report the precision of a measurement.
Making Measurements: Making Measurements: Standard DeviationStandard Deviation
45
Exponential or Scientific Notation:Exponential or Scientific Notation:
Most often in science, numbers are expressed in a format the conveys the order of magnitude.
3285 ft = 3.285 103 ft
0.00215kg = 2.15 103 kg
Mathematics of ChemistryMathematics of Chemistry
46
1.23 104
Coefficient or Mantissa
(this number is 1 and
<10 in scientific notation
Base Exponent
Exponential part
Exponential or Scientific NotationExponential or Scientific Notation
47
Significant figures: Significant figures: The number of digits represented in a number conveys the precision of the number or measurement.
A mass measured to 0.1g is far less precise than a mass measured to 0.0001g.
1.1g vs. 1.0001g1.1g vs. 1.0001g(2 sig. figs. vs. 5 sig. figs)
In order to be successful in this course, you will need to master the identification and use of significant figures in measurements and calculations!
Mathematics of ChemistryMathematics of Chemistry
48
1. All non zero numbers are significant2. All zeros between non zero numbers are
significant3. Leading zeros are NEVER significant.
(Leading zeros are the zeros to the left of your first non zero number)
4. Trailing zeros are significant ONLY if a decimal point is part of the number. (Trailing zeros are the zeros to the right of your last non zero number).
Counting Significant FiguresCounting Significant Figures
49Determining Significant FiguresDetermining Significant Figures
Determine the number of Sig. Figs. in the following numbers
4 sf
7 sf
3 sf
5 sf
3 sf
4 sf
4 sf
1256
1056007
0.000345
0.00046909
0.08040
zeros written explicitly behind the decimal are significant…
not trapped by a decimal place.
1780
770.0
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1. Find the last digit that is to be kept.2. Check the number immediately to the right:
If that number is less than 5 leave the last digit alone.If that number is 5 or greater increase the previous digit by one.
Rounding NumbersRounding Numbers
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11000001056007
0.000345
1780
0.00035
1800
Rounding NumbersRounding Numbers
Round the following to 2 significant figures:
52
Multiplication/Division
The number of significant figures in the answer is limited by the factor with the smallest numbersmallest number of significant figures.
Addition/Subtraction
The number of significant figures in the answer is limited by the least precise numberleast precise number (the number with its last digit at the highest place value).
NOTE: counted numbers like 10 dimes never limit calculations.
Sig. Figures in CalculationsSig. Figures in Calculations
53
Determine the correct number of sig. figs. in the following calculation, express the answer in scientific notation.
23.50 0.2001 174 sf 4 sf 2 sf
= 1996.501749 10 sf
Your calculator knows nothing of sig. figs. !!!Your calculator knows nothing of sig. figs. !!!
from the calculator:
Sig. Figures in CalculationsSig. Figures in Calculations
54
Determine the correct number of sig. figs. in the following calculation, express the answer in scientific notation.
in sci. notation: 1.996501749 103
Rounding to 2 sf: 2.0 103
Sig. Figures in CalculationsSig. Figures in Calculations
55
Determine the correct number of sig. figs. in the following calculation:
391 12.6 + 156.1456
Sig. Figures in CalculationsSig. Figures in Calculations
56
To determine the correct decimal to round to, align the numbers at the decimal place:
One must round the calculation to the least significant decimal.
391 12.6 +156.1456
39112.6
+156.1456
no digits hereno digits here
Sig. Figures in CalculationsSig. Figures in Calculations
57
one must round to here391-12.6
+156.1456
534.5456 (answer from calculator)
round to here (units place)
Answer: 535
Sig. Figures in CalculationsSig. Figures in Calculations
58
Combined Operations:Combined Operations: When there are both addition & subtraction and or multiplication & division operations, the correct number of sf must be determined by examination of each step.
Example: Complete the following math mathematical operation and report the value with the correct # of sig. figs.
(26.05 + 32.1) (0.0032 + 7.7) = ???
Sig. Figures in CalculationsSig. Figures in Calculations
59
Example: Complete the following math mathematical operation and report the value with the correct # of sig. figs.
(26.05 + 32.1) (0.0032 + 7.7) = ???
1st determine the correct # of sf in the numerator (top)
2nd determine the correct # of sf in the denominator (bottom)
The result will be limited by the least # of sf (division rule)
Sig. Figures in CalculationsSig. Figures in Calculations
60
26.05
+ 32.1
0.0032
+ 7.7
3 sf
2 sfThe result
may only have 2 sf
=58.150
7.7032
Sig. Figures in CalculationsSig. Figures in Calculations
61
2 sig figs!
3 sig figs
7.7032
58.150
= 7.5488 = 7.5
2 sfRound to here
Carry all of the digits through the calculation and round at the end.
Sig. Figures in CalculationsSig. Figures in Calculations
62
Dimensional Analysis:Dimensional analysis converts one unit to another by using conversion factors (CFconversion factors (CF’’s)s)..
The resulting quantity is equivalent to the original quantity, it differs only by the units.
= unit (2)unit (1) conversion factorconversion factor
Problem Solving and Problem Solving and Chemical ArithmeticChemical Arithmetic
63
Dimensional Analysis:Dimensional Analysis:Dimensional analysis converts one unit to another by using conversion factors (CFconversion factors (CF’’s)s)..
Conversion factors come from equalities:
1 m = 100 cm
1 m
100 cmor
1 m
100 cm
Problem Solving and Problem Solving and Chemical ArithmeticChemical Arithmetic
64
Exact Conversion FactorsExact Conversion Factors:: Those in the same system of units
1 m = 100 cm
Use of exact CF’s will not affect the significant figures in a calculation.
Examples of Conversion FactorsExamples of Conversion Factors
65
1.000 kg = 2.205 lb
SI unitsSI units British Std.British Std.
Use of inexact CF’s will affect significant figures.
(4 sig. figs.)
Inexact Conversion FactorsInexact Conversion Factors:: CF’s that relate quantities in different systems of units
Examples of Conversion FactorsExamples of Conversion Factors
66
• Problem solving in chemistry requires “critical thinking skills”.
• Most questions go beyond basic knowledge and comprehension. (Who is buried in Grant’s tomb?)
• You must first have a plan to solve a problem before you plug in numbers.
• You must evaluate the result to see if it makes sense. (units, order of magnitude)
• You must also practice to become proficient because...
Chem – is – tryChem – is – try
Problem Solving and Problem Solving and Chemical ArithmeticChemical Arithmetic
67
• Before starting a problem, devise a “Strategy MapStrategy Map”.
• Use this to collect the information given to work your way through the problem.
• Solve the problem using Dimensional Analysis.
• Check to see that you have the correct units along the way.
Problem Solving and Problem Solving and Chemical ArithmeticChemical Arithmetic
68
Most importantly, before you start...
PUT YOUR CALCULATOR DOWN!PUT YOUR CALCULATOR DOWN!
Your calculator wont help you until you are ready to solve the problem based on your strategy map.
Problem Solving and Problem Solving and Chemical ArithmeticChemical Arithmetic
69
ExampleExample: How many meters are there in 125 miles?
First: Outline of the conversion:
Problem Solving and Problem Solving and Chemical ArithmeticChemical Arithmetic
70
ExampleExample: How many meters are there in 125 miles?
First: Outline of the conversion:
m miles ft in cm
Each arrow indicates the use of a conversion factor.
Problem Solving and Problem Solving and Chemical ArithmeticChemical Arithmetic
71
ExampleExample: How many meters are there in 125 miles?
2.54 cm
1 in =
Second: Setup the problem using Dimensional Analysis:
m miles ft in cm
Problem Solving and Problem Solving and Chemical ArithmeticChemical Arithmetic
72
ExampleExample: How many meters are there in 125 miles?
Third: Check your sig. figs. & cancel out units.
m
2.54 cm
1 in =
miles ft in cm
3 sf exact exact exact3 sf
Problem Solving and Problem Solving and Chemical ArithmeticChemical Arithmetic
//
/ // /
/ /
73
ExampleExample: How many meters are there in 125 miles?
Fourth: Now use your calculator. :
m
2.54 cm
1 in/
//
//
//
/ =
miles ft in cm
3 sf exact exact exact3 sf
Carry though all digits, round at end
Problem Solving and Problem Solving and Chemical ArithmeticChemical Arithmetic
74
ExampleExample: How many meters are there in 125 miles?
2.54 cm
1 in
//
/
2.01168 105
=
or 2.01 105 m (3 sf)
3 sf exact exact exact3 sf
Lastly: Check your answer for sig. figs & magnitude.
m
//
miles ft in cm
///
Problem Solving and Problem Solving and Chemical ArithmeticChemical Arithmetic
75
ExampleExample: How many square feet are there in 25.4 cm2?
Map out your conversion:
ft2
//// 2.73403 10-2
ft2=
cm2 in2
or 2.73 10-2 ft2 (3 sf)
3 sf exact exact
Problem Solving and Problem Solving and Chemical ArithmeticChemical Arithmetic
76
ExampleExample: How many cubic feet are there in 25.4 cm3?
Map out your conversion:
ft3
//// 8.96993 10-4
ft3=
cm3 in3
or 8.97 10-4 ft3 (3 sf)
3 sf exact exact
Problem Solving and Problem Solving and Chemical ArithmeticChemical Arithmetic
77
ExampleExample: What volume in cubic feet would 0.851 grams of air occupy if the density is 1.29 g/L?
Map out your conversion:
ft3 L in3 cm3 g
/
3 sf
3 sf3 sf 3 sf exact3 sf
//
//
//
/
Problem Solving and Problem Solving and Chemical ArithmeticChemical Arithmetic
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