chemistry ch 1.pptx
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Chapter 1 Basic Concepts of Chemistry
1.1 Chemistry and its Methods
Hypothesis: A tentative explanation or predictionbased on experimental observations.
Law: A concise verbal or mathematical statement
of a behavior or a relation that seems always tobe the same under the same conditions.
Theory: a well-tested, unifying principle that
explains a body of facts and the laws based onthem. It is capable of suggesting new hypotheses
that can be tested experimentally.
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States of
matter
rigidity Expansion
on heating
compressibility
Solid Rigid Slight SlightLiquid Flows and
assumes
shape ofcontainer
Slight Slight
Gas Fills any
containercompletely
Expands
infinitely
Easily
compressed
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States of Matter and Kinetic-Molecular Theory
All matter consists of extremely tiny particles
that are in constant motion.Solids: are packed closely and in a regular array
Liquids: (considered fluid) are arranged
randomly rather than in a pattern
Gases: (considered fluid), particles of gas are far
apart, move extremely rapidly and not
constrained by their neighbors, fill container
The higher the temperature (T), the faster
the particles move.
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Pure substance
A pure substance cannot be separated into 2 or
more different species by any physical techniqueat ordinary temperatures (T).
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Mixtures: Homogeneous and heterogeneous
A mixture consists of 2 or more pure substances
that can be separated by physical techniques.
Heterogeneous: the properties in a region are
different from those in another region, example,sand at the beach, milk. See next slide
Homogeneous: mixture consists of 2 or moresubstances in the same phase, often called
solution, examples, air, gasoline
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milk
Water (H2O)
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1.4 Elements
Composed of only one type of atom.
An atom is the smallest particle of an elementthat retains the characteristic chemical
properties of that element.
Know the elements. Derived mostly fromLatin, Greek, German, etc. (named after people,
countries, planets, etc)
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Na: sodium (Latin, Natrium)
K: potassium (Latin, Kalium)
Pb: lead (Latin, plumbum meaning heavy)
He: helium (Greek, helios, sun)
Ag: silver (Latin, argentum)
Au: gold (Latin, aurum)
Fe: iron (Latin, ferrum)
Cu: copper (Latin, cuprum)W: tungsten (German, Wolfram)
Clicker Q: What is symbol for hydrogen?
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1.5 Compounds
A pure substance like sugar, salt or water, which
is composed of 2 or more different elementsheld together by chemical bonds is a chemical
compound. No limit to the # of compounds
there appears to be.
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1.6 Physical Properties
Properties that can be observed and measured
without changing the composition of asubstance. Examples: color, mp, bp, density,
state (s,l,g), solubility, electric conductivity,
malleability, ductility, viscositySee next slide
Density = mass / volume
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Extensive and intensive properties
Extensive property: depends on the amount of a
substance present. Example: Mass and volume
Intensive property: does not depend on the
amount of a substance present. Example: mp,bp, density
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1.7 Physical and Chemical Changes
Changes in physical properties are called physical
changes. The identity of the substance ispreserved even though it may have changed its
physical state or gross size. Melting, vaporization
etc.
Chemical change: one or more substances
(reactants) are transformed into one or more
different substances (products)
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Chemical equation showing chemical change.
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1.8 Energy: Some Basic
Principles
Definition: capacity to do work.
Energy can be classified as
kinetic or potential.
Kinetic energy is energy
associated with motion.
Potential energy results from an
objects position.
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Conservation of Energy
Law of Conservation of Energy states that
energy can neither be created nor destroyed(the total energy of the universe is constant).
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The tools of quantitative chemistry
1 units of measurement
Metric system is the scientific system used.SI: International System of Units (Systme
International dUnits)
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Temperature Scales
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The Celsius Temperature Scale (C)
Celsius, a Swedish astronomer (early 1700s)
Water freezes at (clicker Q:just input the number)and boils at (clicker Q:just input the number).
The Kelvin Temperature Scale (K)Named after William Thomson known as Lord
Kelvin. Also known as absolute 0. Absolute 0 is 0K
which is -273C. Kelvin scale doesnt put behindnumber. Kelvin and Celsius degrees are the same
size (see next slide).
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The Fahrenheit Temperature Scale (F)
Devised by Gabriel Fahrenheitearly 1700s -
(German instrument maker)C = (F-32) / 1.8 F = 1.8 x C + 32
Conversions:
Clicker Q: 85F is what in Celsius?
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Conversion from one to the other.
25C is how many kelvins?
Clicker Q: 38C is how many kelvins?
400 K is how many C
Clicker Q: 1000 K is how many C?
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Length, Volume, and Mass
Length
Meter is the standard unit of length.
1 m = 100 cm 1000 m = 1 km 1 in = 2.54 cm
Conversions
Clicker Q: 1 cm is how many mm?
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Table R-2, p. 26
Know these.
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Volume
1 liter = 1000 ml = 1000 cm3 1 gal = 3.785 l
So 1 ml = 1 cm3 (used in medicine, cc)1 dl = 100 ml widely used in medicine
Conversions
Clicker Q: How many liters are in 750 ml?
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Mass
SI unit is the kg
1 kg = 1000 g 1 g = 1000 mg 1 lb = 454 g1 kg = 2.205 lbs
Conversions.
Clicker Q: how many g are in 540 mg?
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Energy units
SI unit is the joule (J)
1 J = 1 kgm2/s2 1 J = 4.184 calories1000 J = 1 kJ
Dietary calorie is actually 1000 kcal usuallyabbreviated Cal
Interesting: How do we determine the caloriecontent of food? Atwater system: 1 g protein, 1 g
carbohydrate = 4 kcal, 1 g of fat = 9 kcal, 1 g ofalcohol = 7 kcal
Clicker Q: 2300 J is how many kJ
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2 Making Measurements: Precision, Accuracy,
and Experimental Error
Theprecisionof a measurement indicates howwell several determinations of the same
quantity agree.
Accuracyis the agreement of a measurementwith the accepted value of the quantity.
Accuracy is often reflected by Experimental
error.
=
Experimental value Accepted valuePercent Error 100
Accepted value
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The precision of a measurement indicates how well
several determinations of the same quantity agree.
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3 Mathematics of Chemistry
Exponential or Scientific Notation
Scientific notation is used to present very large
or very small numbers.
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Clicker Q: Express this number in normalnotation 1.23 x 103
Clicker Q: Express this number in normal
notation 1.23 x 10-3
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Significant figures: The number of digitsrepresented in a number conveys the precision ofthe number or measurement.
A mass measured to 0.1g is far less precise than a
mass measured to 0.0001g.1.1g vs. 1.0001g
(2 sig. figs. vs. 5 sig. figs)
In order to be successful in this course, you willneed to master the identification and use ofsignificant figures in measurements andcalculations!
Significant Figures
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Significant figures
Exact numbers: number of eggs in a dozen, # of
people in a locked roomSignificant figures indicate the uncertainty in
measurements.
See next slides
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36
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1
2
3
4
5
6
7
8
9
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38
Clicker Q: How wide is the paper to the best
of your ability to measure it?
7
8
9
Rules for sig figs
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Rules for sig figs
1. Nonzero digits are always significant.
123.2 cm
1357.98 ml
Clicker Q: How many sig figs?
2. Zeroes are sometimes significant.
0 at beg. of # to position decimal pt never sig
0.123 mg
0.0001598 g
0.015 g Clicker Q: # of sig figs?
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0 between nonzero digits are always sig.
102 g
2.08 milesClicker Q: # of sig figs?
0 at end of # that contains a dec pt are always sig
1.20 g
60.000 g
0 at end of # that doesnt contain a dec. pt may or
may not be sig
24,500 m ?
3 E # i li i d # f i fi (
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3. Exact # contains an unlimited # of sig fig (e.g.
12 eggs, or 1 yard = 3 feet)
A dozen eggs is how many?Clicker Q: 1 m is how many cm?
Clicker Q: 1 ft is how many inches?
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Significant Figures
Examples:
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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.
Examples:
Clicker Q: Round this number to 3 sig figs
Rounding Numbers
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Multiplication/Division
The number of significant figures in the answer is
limited by the factor with the smallest numberof
significant figures.
Sig. Figures in Calculations
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45
Multiplication & Division rule
Easier of the two rules.
Product has the smallest number of
significant figures of multipliers
5.22tooffround
21766.5
31.2x
224.4
3.9tooffround
89648.3
41.x
2783.2
A calculated number can NEVER be more
precise than the numbers used to calculate it.
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1.25 cm by 0.25 cm by 10. mm - volume in cm3
Clicker Q: A box is 2.5 cm by 1.54 cm by 1.233 cm.
What is the volume in cm3?
Addition/Subtraction
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Addition/Subtraction
The number of significant figures in the answer is
limited by the least precise number(the numberwith its last digit at the highest place value).
NOTE: counted numbers like 10 dimes never limit
calculations.
6.95tooffround
9463.6
20.2
423.1
3692.3
6.671tooffround
6707.6
312.2
7793.8
20 4
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20.4
1.322
83104.722
12.4 + 1.78 - 10.008
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Combined Operations:When there are both
addition & subtraction and or multiplication &
division operations, the correct number of sfmust
be determined by examination of each step.
(26.05 + 32.1) (0.0032 + 7.7) = ???
Sig. Figures in Calculations
Clicker Q: 81 262 4 47 + 1 3 x 102
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Clicker Q: 81.2624.47 + 1.3 x 102
3.67
How many sig figs will answer have?
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4 Problem Solving by Dimensional Analysis
Dimensional Analysis:
Dimensional analysis converts one unit toanother by using conversion factors (CFs).
The resulting quantity is equivalent to the
original quantity, it differs only by the units.
Examples:
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Examples:
Clicker Q: convert 19.3 g/cm3to kg/ml
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5 Graphs and Graphing
Straight line equation: y = mx + b
m = slope = rise/ run
b = y-intercept, value of y where x =0
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Fig. R-11, p. 41
bl l i d
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6 Problem Solving andChemical Arithmetic Before starting a
problem, devise aStrategy Map.
Use this to collect theinformation given to
work your way throughthe problem.
Solve the problem usingDimensional Analysis.
Check to see that youhave the correct unitsalong the way.
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p. 31
6 materials with
different densities. The
liquid layers are gasoline
(top), water (middle),
mercury (bottom). A
cork floats on gasoline.A piece of oak wood
sinks in gasoline but
floats on water. Brasssinks in water but floats
on mercury.
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p. 33
What are these liquids?
Cli k Q K i h d i / l
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Clicker Q: Knowing that density = mass/volume
Calculate the density of a substance that has a
mass of 12.5 g and occupies a volume of 150. ml.Calculate density in g/ml. Enter just the number
into the clicker.
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What volume in ml would 0.851 grams of air
occupy if the density is 1.29 g/L?
The water level in a graduated cylinder stands at
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The water level in a graduated cylinder stands at
20.0 ml before and at 26.2 ml after a 16.74 g
metal bolt is submerged in the water.
Clicker Q: What is the volume of the bolt?
What is the density of the bolt?