Chapter 1 Chemical Foundations

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Chapter 1Chemical Foundations

• CHY 115 General Chemistry I

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Chapter Outline

• Overview of chemistry
• Methods of science
• Measurements
• Unit systems
• Quantities measured
• Taking measurements
• Accuracy and precision, types of error
• Significant figures and calculations
• Dimensional analysis
• Temperature
• Density
• Classification of matter

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Chemistry

• Chemistry study of the matter of the universe
  and the changes that this matter undergoes
• Matter anything that has mass and occupies
  space
• Examples of matter and non-matter

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Chemistry

• What chemists study about the matter
• Composition
• Structure
• Properties
• Chemical changes the matter will undergo
• Relationship between the matter and
• The environment
• Human health

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Better living (?) through chemistry
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The Scientific Method (1.2)

• The scientific method describes a framework by
  which science is conducted.
• Scientific method has been described as organized
  common sense.
• Methodical approach to problem-solving.

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Scientific Method

• Observations ? questions
• Develop hypotheses to explain observations
• Test hypotheses
• Make predictions, if hypothesis is true then.
• Test accuracy of the prediction
• Repeat the process, test new hypotheses
• Analyze results and share findings and conclusions

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Scientific Inquiry

• Observations ? Questions
• Observations must be recordable and repeatable
• Observations may be
• Quantitative
• or
• Qualitative

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Scientific Inquiry

• Develop and test hypotheses
• Hypothesis tentative explanation of the
  observations based on limited data
• Make predictions based on the hypothesis
• Test accuracy of the prediction
• Data collected generates new observations which
  in turn, often leads to more hypotheses to test
• Repeat for all hypotheses

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Scientific Inquiry

• Analyze results and share findings and
  conclusions
• Publish results in journals
• Present findings at conferences..
• Public versus Private Research

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Types of Research

• Basic research
• scientific research for the sake of knowledge, no
  immediate application in mind.
• Applied research
•  scientific research with the short-term goal of
  solving a specific problem
• begin the research with an application in mind.

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Theories

• After significant research theories/models are
  developed to explain the observations
• Theory well-tested explanation of some part of
  nature that explains a broad range of
  observations
• Supported by significant data
• Subject to rigorous testing and revision when
  needed

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Natural Law versus Theory

• Natural Law
• Statement/summary of observed behavior
• Law of conservation of matter
• Theory (also called a model)
• Explanation of observed behavior based on
  significant data
• Theories attempt to explain laws

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Factors Impacting Scientific Inquiry

• The direction of scientific research is impacted
  by many factors
• Theories and technology of the day
• Money
• Religion
• Politics
• World conditions

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Units of Measure (1.3)

• Much of chemistry is based on analysis of
  quantitative observations
• A quantitative observation is obtained by
  measurement and includes a number and a unit.

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Unit Systems

• English system
• Used in United States
• Metric system
• Used in science
• International system (SI)
• Based on the metric system
• UNITS MATTER!

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Unit Systems

• English System
• Used in U.S.
• Little logic to the units
• Examples

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Unit Systems

• Metric System
• Developed in the late 1700s and adopted after
  the French Revolution
• A base (or fundamental) unit is defined for each
  quantity measured
• The size of the base unit can be modified by
  adding a prefix

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Unit Systems - metric

• Quantity Base unit Symbol

Length Meter m
Mass Gram g
Volume Liter L or l
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Unit Systems - meteric

• Metric Prefixes, see page 9

Mega M 106
Kilo k 103
BASE L, m, g 100
Deci d 10-1
Centi c 10-2
Milli m 10-3
Micro m or mc 10-6
Nano n 10-9
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Unit Systems

• Using prefixes
• Base unit meter
• Kilometer km _________ m

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Unit Systems

• International System (SI)
• Adopted in 1960
• Internationally agreed upon set of units
• Used in industry and science
• See page 9

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What chemists measure

• Length distance between 2 points
• Metric base _____________
• Mass quantity of matter present
• Base unit __________
• Weight measure of gravitational pull on an
  object
• Base unit ___________

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Mass and Weight

• Measure mass on a balance.
• Measure weight on a scale.

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Volume

• Volume amount of three dimensional space
  occupied by an object
• SI base meter3
• Metric base Liter dm3
• dm ______ cm
• dm3 ___________ cm3
• Equivalent units
• mL _______ ________

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Uncertainty in Measurement (1.3)

• All measurements include some degree of
  uncertainty
• A properly taken measurement includes all of the
  certain digits and one uncertain (estimated) digit

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Taking measurements

• When taking a measurement you record
• All known digits
• those marked on the measuring device
• One estimated digit
• A multiple of 1/10 the smallest marked unit on
  the measuring device

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Taking measurements

• Thermometer example
• Graduated cylinder example

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Accuracy and Precision

• Accuracy how close a measured value agrees with
  the true value
• Ideally values will differ in only the estimated
  digit

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Accuracy and Precision

• Precision how closely repeated measurements
  agree with each other
• Ideally the values will differ in only the
  estimated digit

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Evaluating a measuring device

• Good measuring devices are both accurate and
  precise
• Readings taken with a precise, but not accurate
  measuring device can be corrected.

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Types of Errors

• Random error
• Value has an equal probability of being high or
  low
• Compensate for random errors by
• Systematic error
• Value recorded is consistently low or high
• Compensate for systematic errors by

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Significant Figures and Calculations (1.5)

• A measurement includes all the certain digits and
  one estimated (uncertain) digit
• These digits are called the significant figures
  of a measurement.
• All calculations based on measurements must
  reflect the uncertainty of the original
  measurements.

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Significant Figures

1. Rules for counting significant figures
2. Rules for rounding off calculations based on
   significant figures

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Counting Significant Figures

• All nonzero integers are significant.
• 35.76 g _______ sig. fig.

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Counting Significant Figures

• Zeros
• Leading zeros are NEVER significant
• 0.0037 mL _____ sig fig
• Captive zeros are ALWAYS significant
• 7.098 g ______ sig. fig.

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Counting Significant Figures

• Zeros
• Trailing zeros are significant only if the value
  includes a decimal place.
• 3570 g ______ sig. fig.
• 7.500 kg ______ sig. fig.

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Counting Significant Figures

• Exact Numbers have unlimited significant figures
• Numbers obtained by counting
• 23 students
• Definitions
• 1 foot 12 inches
• 1 inch 2.54 cm (exactly)

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Rules for Rounding Off

• If the first digit to be removed is
• Less than 5, the preceding digit remains the same
• 5 or greater, the preceding digit is increased by
  1

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Significant Figures and Calculations

• Multiplication and Division
• The answer is rounded to the same number of sig.
  fig. as the measurement with the fewest sig. fig.
• (3.50 x 102 mL) x 0.7030 g/mL

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Significant Figures and Calculations

• Addition and Subtraction
• The answer is rounded to the same number of
  decimal places as the measurement with the fewest
  decimal places.
• 32.05 g 5.3978 g 6.30 g

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Dimensional Analysis (1.6)

• Convert the number of minutes left in class to
  seconds.
• Open to Appendix A26
• PRACTICE!

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Dimensional Analysis

• The largest pumpkin at last years Windsor fair
  weighed 673 pounds.
• Express the mass of this pumpkin in grams and in
  kg.

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Dimensional Analysis

• A block of wood has a volume of 2.50 ft3.
• Express the volume of the wood block in cm3.

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Dimensional Analysis

• The world's oceans have a surface area of
  361,100,000 square kilometers.
• Express this surface area in square miles. Please
  put your final answer in scientific notation.

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Dimensional Analysis

• Water has a density of .998 g/mL at room
  temperature.
• Express the density of water in pounds/gallon.
• Game plan?

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Temperature (1.7)

• Temperature Scales (units)
• Fahrenheit (0F)
• Used in this country
• Celsius (0C)
• Used in the physical science
• Kelvin (K)
• SI unit for temperature
• Used in gas law calculations

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Temperature
Fahrenheit Celsius Kelvin
Boiling point water
Degrees between fp and mp
Freezing point water
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Temperature
Fahrenheit 0F Celsius 0C Kelvin K
Boiling point water 212 100 373.15
Degrees between fp and bp 180 100 100
Freezing point water 32 0 273.15
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Temperature Conversions

• TK TC 273.15
• TC (TF - 32)
• 1.8
• TF (1.8) TC 32

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Temperature Conversions

• Express 68.20 F in in 0C and in K
• Express 78.50 C in 0F.
• Express room temperature in K.

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Density (1.8)

• Density mass of an object
• volume of object
• Density is a physical property that is often used
  to identify an object (along with bp and mp)

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Density

• Density mass of an object
• volume of object
• Mass - is expressed in grams
• Volume is expressed in
• mL or cm3 for solids and liquids
• L for gases

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Density

• Density units
• Solids and Liquids
• g/mL or g/cm3
• Gases
• g/L
• English System
• Pounds/foot3

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Density

• Density of water is 1g/mL at room temperature.
• What is the approximate mass of water in a 0.5 L
  water bottle?
• What is the volume of 150 grams of water?

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Density - FYI

• Objects with a density greater than 1g/mL sink in
  water.
• Objects with a density less than 1g/mL float in
  water.

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Density - FYI

• The density of the elements can be found on the
  periodic table.
• Examples
• The density of compounds must be looked up in
  reference books.

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Density

• Calculating density
• Convert data to the appropriate units
• Plug data into the density formula
• Round answer to the correct number of sig. fig,

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Using Density in Calculations

• What is the mass in pounds of a stack of boards
  that measures 4.0 feet by 4.0 feet by 8.0 feet if
  the density of the wood is 0.74 g/cm3.
• Game plan?

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Classification of Matter(1.9)

• Physical states
• Solid, liquid gas
• Physical and chemical properties
• Composition
• Pure substances - Elements and compounds
• Mixtures - Homogeneous and heterogeneous

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Physical States of Matter

• A substances state of matter is related to the
  strength of the attractive forces among the
  matters particles
• E.g. solids have very strong attractive forces
  between particles and gases very weak forces

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Solids

• Shape
• fixed/definite
• Volume
• fixed
• Varies slightly with temperature
• Particles are closely packed, rigidly arranged,
  and strongly attracted to each other

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Liquids

• Shape
• A liquid takes the shape of the bottom of the
  container up to the volume it fills
• Volume
• fixed/definite
• Varies slightly with temperature
• Particles are sliding over each other and
  moderately attracted to each other

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Gases

• Shape and Volume
• A gas takes the shape and volume of a closed
  container
• Gases expand or compress to fill a closed
  container
• Gas particles are far apart, moving very rapidly
  as they bounce off each other and the walls of
  the container
• Gas particles are very weakly attracted to each
  other

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Properties of Matter

• Physical property
• Characteristic of a substance that can be
  determined without changing the chemical
  composition of the substance
• Physical change
• Change in a substances physical properties
  without a change in chemical composition

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Properties of Matter

• Chemical property ability of a substance to
  form new substances
• Always involves a change in chemical composition
  of the substance
• Chemical change
• Change in a substances chemical composition
• Also called a chemical reaction

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Composition of Matter

• Pure Substance - matter with definite composition
• Elements and compounds are pure substances
• Mixture matter with variable composition
• 2 or more pure substances present
• Not chemically joined/bonded to each other

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Pure Substances

• Element substance that cannot be broken down
  into other substances by chemical means
• Compound 2 or more (different) elements joined
  in a definite ratio
• Compounds can be broken down into elements by
  chemical means

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Mixtures

• Mixture matter with variable composition
• 2 or more pure substances mixed together
• The components of a mixture are not joined to
  each other in any fixed ratio

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Mixtures

• Homogeneous mixture
• Mixture with the same properties throughout
• Also called a solution
• Examples
• Heterogeneous mixture
• Mixture with regions that have different
  properties
• Examples

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Practice

• 67 on page 34
• 71 on page 35

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Separating Mixtures

• Most matter in the world is a mixture
• To separate the components of a mixture, chemists
  take advantage of differences in the physical
  properties of the mixtures components.
• Not always easy!

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Separating Mixtures

• Filtration
• Used to separate a solid from a liquid in a
  heterogeneous mixture

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Separating Mixtures

• Can filtration be used to separate sugar from
  water in sugar water?
• Why or why not?

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Separating Mixtures

• Distillation
• Separates mixtures based upon differences in
  volatility
• Volatility
• Volatility is related to a substances boiling
  point
• A highly volatile substance will have a _______
  boiling points.

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Distillation

• Distillation works best when there is at least a
  100 C difference in boiling points.
• Consider a mixture of water and ethanol.
• Boiling point water ____________
• Boiling point ethanol ______________

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Distillation Apparatus
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Distillation

• Heat the mixture to the b.p. of the substance
  with the lower b.p.
• Change of state occurs
• Ethanol becomes a gas
• Ethanol vapors expand to fill the distillation
  apparatus

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Distillation

• Ethanol gas enters the water cooled condensing
  tube
• Change of state occurs as the ethanol is cooled
  below __________
• Ethanol gas condenses and forms a liquid
• Ethanol liquid drips into the collecting container

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Distillation

• Temperature shoots up to the bp of water
• Change of state occurs
• Water becomes a gas
• Water vapors expand to fill the distillation
  apparatus
• Water vapors enter the condensing tube
• Water condenses to form a liquid