Download Chapter 1 - Continued Models in Chemistry 1.1 The Discovery Process

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 1 - Continued
29 August 2013
Chemistry:
1.1 The Discovery Process
Methods and Measurement
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 coded balls
– sticks show attractive forces
holding atoms together
1
1.2 Matter and Properties
• Properties - characteristics of matter
– chemical vs. physical
• Ways to categorize matter
1… by state
2… by composition
1.2 Matter and Properties
• Three states of matter
1. 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
2
Three States of Water
(a) Solid
(b) Liquid
(c) Gas
Comparison of the Three Physical
States
Not all matter exists in all three states
3
1.2 Matter and Properties
• 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.
4
1.2 Matter and Properties
1.2 Matter and Properties
• 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
Classify the following as either a
chemical or physical property:
a. Color
b. Flammability
c. Hardness
d. Odor
e. Taste
5
1.2 Matter and Properties
Classify the following as either a
chemical or physical property:
1.2 Matter and Properties
Classify the following as either a
chemical or physical change:
a. Color - physical
b. Flammability - chemical
c. Hardness - physical
d. Odor - chemical
e. Taste - chemical
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
6
1.2 Matter and Properties
Classify the following as either a
chemical or physical change:
1.2 Matter and Properties
• Intensive properties - a property
of matter that is independent of the
quantity of the substance
a. Boiling water becomes steam (ph)
b. Butter turns rancid (ch)
c. Burning of wood (ch)
d. Mountain snow pack melting in
spring (ph)
e. Decay of leaves in winter (ch)
- Density
- Specific gravity
- Battery voltage
• Extensive properties - a property
of matter that depends on the
quantity of the substance
- Mass
- Volume
- Battery capacity
7
1.2 Matter and Properties
1.2 Matter and Properties
Classification of Matter
• 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
• 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
8
1.2 Matter and Properties
Classification of Matter
• 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,
1.2 Matter and Properties
random placement
Classes of Matter
a - pure substance
b - homogeneous mixture
c - heterogeneous mixture
9
1.3 The units of measurement
Units - the basic quantity of mass, volume or
whatever quantity is being measured
– A measurement is useless without its 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
Metric System Units
• Mass - the quantity of matter in an object
– not synonymous with weight
– standard unit is the gram (g)
– The pound (lb) is the common English unit.
1 lb = 454 g
• Mass must be measured on a balance (not a scale)
10
• Length - the distance between two points
– standard unit is the meter (m)
– The yard is the common English unit.
1 yd = 0.91 m
• Volume - the space occupied by an object
1.3 The Units of
Measurement
– standard unit is the liter
– The quart is the common English Unit
1 qt = 0.946 l
Volume =
lxwxh
Volume =
1mx1mx1m=
1 m3
1 m3 = 1000 l
1 m = 100 cm
1 m3 = (100)3 cm3 = 1 000 000 cm3
11
1.5 Experimental Quantities
1.3 The Units of
Measurement
The milliliter
(ml) and the
cubic centimeter
(cm3) are
equivalent
• Time
- metric unit is the second
Etymology
An hour was divided twice into a smaller
part (1/60th), in Latin called
pars minuta prima (first small part) and
pars minuta secunda (second small part)
12
Metric System Prefixes
• Basic units are the units of a quantity
without any metric prefix.
1.3 Significant Figures and
Scientific Notation
• Information-bearing digits or figures in a
number are significant figures
• The measuring device 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
13
1.3 Significant Figures and
Scientific Notation
1.3 Significant Figures and
Scientific Notation
Significant figures - all digits in a number
representing data or results that are known
with certainty plus one uncertain digit
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
14
1.3 Significant Figures and
Scientific Notation
1.3 Significant Figures and
Scientific Notation
Use 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 [but
there is a better way to write this]
• Zeros to the left of the first nonzero integer
are not significant.
• 0.0032 has two significant digits
How many significant figures are in
the following?
1. 3.400
2. 3004
3. 300.
[3.00 x 102]
4. 0.003040
15
1.3 Significant Figures and
Scientific Notation
1.3 Significant Figures and
Scientific Notation
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 103
• What if you want to show the above
number has four significant figures?
= 5.340 x 103
16
1.3 Significant Figures and
Scientific Notation
1.3 Significant Figures and
Scientific Notation
Calculator note:
103
should be entered as EE 3
NOT
10EE3
• To convert a number smaller 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
17
1.3 Significant Figures and
Scientific Notation
• Conversion to scientific notation will
allow to write numbers with
significant figures without the
artificial period at the end of a
number
100. can be written as 1.00x102
• The decimal period without a
decimal number is actually wrong, so
avoid it (legibility, end of sentence)
• Also, write a zero before decimal
point. 0.11 is correct, .11 is not
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
measurements
18
1.3 Significant Figures and
Scientific Notation
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
6.71862
108.428
152.82662
liters
liters
liters
liters
correct answer 152.83 liters,
count the decimal here
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:
56.71862 liters
98.428 liters
155.14662 liters
correct answer 152.146 liters, count the
decimal here, note the number has one
more sig. figure than you might think.
19
1.3 Significant Figures and
Scientific Notation
1.3 Significant Figures and
Scientific Notation
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
4.2  103 (15.94)
 2.9688692 10 8 (on calculator)
4
2.255  10
Which number has the fewest
significant figures? 4.2 x 103 has only 2
The answer is therefore, 3.0 x 10-8
Significant figures - another look
20
1.3 Significant Figures and
Scientific Notation
1.3 Significant Figures and
Scientific Notation
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
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 6 or larger, the
preceding number is increased by one unit
• When the number to be dropped is 5 and is
followed by non-zero numbers, the last figure kept
should be unchanging if the last figure is even, and
increased by one if the last figure is odd.
• Round to 3 significant figures: 3.34966 x 104
=3.35 x 104
21
1.3 Significant Figures and
Scientific Notation
1.3 Significant Figures and
Scientific Notation
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 6 or larger, the
preceding number is increased by one unit
• When the number to be dropped is 5 and is
followed by non-zero numbers, the last figure kept
should be unchanging if the last figure is even, and
increased by one if the last figure is odd.
6.65 to 2 figures ….6.6
6.55 to 2 figures ….6.6
6.45 to 2 figures ….6.4
but 6.4501 to to figures …6.5
How Many Significant Figures?
Round off each number to 3 significant
figures:
1. 61.40
2. 6.171
3. 0.066494
22
1.3 Significant Figures and
Scientific Notation
How Many Significant Figures?
Round off each number to 3 significant
figures:
1. 61.40
61.4
2. 6.171
6.17
3. 0.066494 0.0665
1.4 Units and Unit Conversion
Data, 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
23
1.4 Units and Unit
Conversion
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
1.4 Units and Unit
Conversion
Basic Units of the Metric System
Mass
Length
Volume
gram
meter
liter
g
m
l
• Basic units are the units of a quantity
without any metric prefix
24