Chapter 1
(Essentials of General Chemistry, 2nd Edition)
(Ebbing and Gammon)
Chemistry and
Measurement
Experiment and Explanantion
Experiment
an observation of natural phenomena
carried out in a controlled manner so
that the results can be duplicated and
rational conclusions obtained
Law a concise statement or mathematical equation
about a fundamental relationship or regularity
in nature (eg. Law of conservation of mass)
Hypothesis a tentative explanation of some
regularity in nature
Theory a tested explanation of basic natural
phenomena
- cannot be proven absolutely (further
experiment may show limits)
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Representation of Scientific Method
Figure 1.7
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Law of Conservation of Mass
Matter - whatever occupies spaces and can be
perceived by our senses
Law of conservation of mass
- the total mass remains constant during a chemical
change (chemical reaction)
- ie. mass is neither created nor destroyed in chemical reactions
Mass versus weight
- weight the force of gravity exerted on an object
- mass weight is proportional to the mass of an
object divided by the square of the distance
between the center of mass of the object and
that of the earth
- mass is the same wherever it is measured
but the weight of an object varies
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Matter: Physical State and Chemical Constitution
Ways of classifying matter:
i.) physical state
ii.) chemical constitution
i.) physical state (state of matter)
solid relatively incompressible and
has fixed shape and volume;
relatively rigid
liquid fixed volume but no fixed
shape; relatively
incompressible fluid
gas will fit into a container of almost
any size and shape; easily
compressible fluid
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Matter: Physical State and Chemical Constitution
ii.) chemical constitution
a.) physical change and chemical change
b.) physical property and chemical property
a.) physical change a change in the form of matter but
not in its chemical identity (eg. changes in physical
state)
chemical change (chemical reaction) a change in
which one or more kinds of matter are transformed
into new matter or several new kinds of matter
b.) physical property characteristic that can be observed
for a material without changing its chemical
identity
chemical property characteristic of a material
involving its chemical change
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Substance
- a kind of matter that cannot be separated into other kinds
of matter by any physical process
Two categories of substances:
a.) element
- a substance that cannot be decomposed by
any chemical reaction into simpler substances
b.) compound
- a substance composed of two or more
elements chemically combined
Law of definite proportions
-a pure compound, whatever its source, always
contains definite or constant proportions of the
elements by mass
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Mixtures
- a material that can be separated by physical means
into two or more substances
- has variable composition, unlike a pure compound
Two types of Mixtures
a.) heterogeneous mixture
- a mixture that consists of physically distinct
parts, each with different properties
b.) homogeneous mixture (or solution)
- a mixture that is uniform in its properties
throughout given samples
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Relationship: Elements, Compounds, and Mixtures
Figure 1.16
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Substances and Mixtures
Some Elements:
arsenic, iodine, magnesium,
bismuth and mercury
Heterogeneous Mixture:
Potassium Dichromate
and iron filings
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Separation of Mixtures
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Measurement and Significant Figures
measurement
- subject to experimental error and repeated
measured values will vary slightly from one another
Presision versus Accuracy
precision refers to the closeness of the set of values
obtained from identical measurements of a
quantity
accuracy refers to the closeness of a single
measurement to its true value
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Significant Figures
- those digits in a measured number (or result of a
calculation with measured numbers) that include all
certain digits plus a final one having some uncertainty
Number of Significant Figures
- the number of digits reported for the value of a
measured or calculated quantity, indicating the
precision of the value
Rules to count the number of significant figures in a given
measured quantity
1.) All digits are significant expect zeros at the beginning
of the number and possibly terminal zeros ( one or
more zeros at the end of a number)
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2.) Terminal zeros ending at the right of the decimal
point are significant
3.) Terminal zeros in a number without an explicit
decimal may or may not be significant
- you can remove any uncertainty in such cases by
expressing the measurement in scientific notation
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Scientific Notation
- the representation of a number in a form
A x 10n
where,
A
a number with a single nonzero digit to the
left of the decimal point
n an integer or whole number
Note: convenient notation for expressing very large or
very small quantities
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Significant Figures in Calculations
Rules:
1.) Multiplication and Division
- when multiplying or diving measured quantities,
give as many sig. figs. In the answer as there are in
the measurement with the least number of sig.figs.
2.) Addition and Subtraction
- when adding or subtracting measured quantities,
give the same number of decimal places in the
answer as there are in the measurement with the
least number of decimal places
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Exact Numbers
- a number that arises when you count items or
sometimes when you define a unit
Rules:
- conventions of sig. figs. do not apply to exact
numbers
- therefore, the number of sig. figs. in a calculation
result depends only on the numbers of sig. figs. in
quantities having uncertainties
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Rounding
- the procedure of dropping nonsignificant digits in
a calculation result and adjusting the last digit reported
Rules (focus on leftmost digit to be dropped)
1.) if this digit is 5 or greater, add 1 to the last digit to be
retained and drop all digits further to the right
2.) if this digit is less than 5, simply drop it and all digits
to the right
Note: - in doing a calculation of two or more steps, it is desirable
to retain nonsignificant digits for intermediate answers
- this ensures that accumulated small errors from
rounding do not appear in the final results
- when using a calculator, enter all numbers one after
the other, performing each arithmetic operation and
rounding only the final answer
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SI Units
International System of Units, SI
(le Systeme International d Unites)
- larger or smaller unit for a physical quantity
is indicated by an SI prefix
- a prefix used to indicate a power of ten
(Table 1.2)
SI base units
the SI units from which all others can be
derived
- focus: length, mass time and temperature
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Table 1.1 SI Base Units
Quantity
Unit
Symbol
Length
meter
m
Mass
kilogram
kg
Time
second
s
Temperature
kelvin
K
Amount of substance
mole
mol
Electric current
ampere
A
Luminous intensity
candela
cd
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Table 1.2 SI Prefixes
Multiple
Prefix
Symbol
106
mega
M
103
kilo
k
10-1
deci
d
10-2
centi
c
10-3
milli
m
10-6
micro
10-9
nano
n
10-12
pico
p
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Length
meter (m)
- SI base unit of length
- when combined with one of the prefixes allows one
to get unit appropriate for any length
measurement
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Mass
kilogram (kg)
- SI base unit of mass
- unusual base unit since it contains a prefix
- in forming other SI mass units, prefixes are
added to the word gram (g)
1 kg
2.2 lbs
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Time
second (s)
- SI base unit of time
- combine this unit with prefixes to create
appropriate unit of measure
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Temperature
- a measure of hotness
thermometer a device for measuring temperature
Three main scales:
1.) Celsius scale (oC)
- temp. scale used in general scientific use
2.) kelvin scale (K)
- SI base unit of temperature
- an absolute temperature scale (lowest temp. that
can be obtained is theoretically zero)
tK = tC x 1K
+ 273.15 K
1oC
Note: Celsius and Kelvin scales have equal-size units
(ie. 0oC equivalent to 273.15 K)
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3.) Fahrenheit Scale
- there are exactly 9oF for every 5oC
tF = tC x 9oF
+
32oF
o
5C
or
tC = 5oC x (tF - 32oF)
9oF
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Temperature Scale Comparison
Figure 1.22
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Derived Units
1.) Volume
- SI unit is cubic meter (m3) since it is
defined as length cubed
- since m3 is a very large, common to use
dm3 cubic decimeter (equal to 1L)
cm3 cubic centimeter
Note: lab glassware is usually calibrated in liters or
milliliters (1000 mL = 1L)
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2.) Density
- mass per unit volume
d=m
where d = density
V
m = mass
V = volume
- is a characteristic property of a
material
- helpful in identifying material or
determining whether substance in
pure
- provides useful relationship
between mass and volume
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Unit and Dimensional Analysis
(Factor-label analysis)
- the method of calculation in which one carries
along the units for quantities
- treat units in same way as algebraic quantities
Benefits:
1.) the units for the answer will come out of the
calculations
2.) if you make an error in arranging factors in the
calculation, this will become apparent because the
final units will be nonsense
conversion factor
- factor equal to 1 that converts a quantity expressed in
one unit to a quantity expressed in another unit
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10
(number · unit)
x
new unit
unit to be converted
= new number · new unit
- generally, set up conversion factor so it cancels out
initial unit
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Relationships of Some U.S. and Metric Units
Length
Mass
Volume
1 in = 2.54 cm
1 lb = 0.4536 kg
1 qt = 0.9464 L
1 yd = 0.9144 m
1 lb = 16 oz
4 qt = 1 gal
1 mi = 1.609 km
1 oz = 28.35 g
1 mi = 5280 ft
Table 1.4
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