Transcript Chapter 2 - Measurements and Calculations

Chapter 2
Suggested Problem Set:
Page 59 #4, 8-13, 16-18, 21-23, 27-30, 32-34, 37-45
Chapter 2 Quizzes: Monday, Wednesday
Unit 1 Test: Friday, August 27
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Le Systeme International d’ Unites (SI)
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All measurements consist of 2 parts
◦ A number and unit
◦ i.e. 15 g, 25 m, 1.2 mol
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SI Base Units
◦ Length
◦ Mass
◦ Time
◦ Temperature
◦ Amount of a Substance
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Derived Units
◦ Units that are derived from 2 or more base units in
combination with one another
◦ i.e. Volume, Density, Velocity, Molar mass,
Concentration, Area, etc.
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Prefixes:
◦
◦
◦
◦
◦
◦
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kilo
deci
centi
milli
micro
nano
pico
What does the prefix giga stand for?
A. 103
B. 106
C. 109
D. 1012
E. 1015
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Density is an important property of matter
that is often used to identify a substance
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It is the ratio of the mass of an object to its
volume
m
D
V
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The density of an object is usually compared
to water which has a density of 1.0 g / ml.
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If the unit for mass is grams and the unit for
volume is cm3, what would density be
measure in?
A. grams
B. cm3
C. g-cm3
D. g/cm3
E. g/ml
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What is the density of a sample of ore that
has a mass of 74.0 g and occupies 20.3 cm3?
What is the volume of a sample of wood that has
a mass of 95.1g and a density of 0.857 g/cm3?
Thickness of Aluminum Foil
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Are used to convert from one unit of measure
to another
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They start with equalities
◦
◦
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◦
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12 inches = 1foot
5280 feet = 1 mile
1 mile = 1.61 km
1 inch = 2.54 cm
Conversion factors are usually just a different
way of writing the number 1
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How many km/min is a car going if it is
traveling at 65 miles/hr?
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How many cm3 are there in 15 in3?
If there are 1600m in a mile, how many
miles is 2000km?
A. 0.0008
B. 1.3
C. 1250
D.3200
E. None of the above is correct
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Accuracy
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Precision
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◦ the closeness to the true value of a measure.
◦ a measure of the reproducibility of a
measurement
You can be precise in a series of
measurements and not accurate, but if you
are accurate in a series of measures, you
are also precise
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Percent error is used often in the laboratory
setting to determine how close your
experimental results are to the actual true
value that they should be.
It is calculate using the following formula
T rue Value Experimental Value
x 100 % Error
T rueValue
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Significant figures are the numbers we
actually count in a calculation
First we must learn how to count them, then
do calculations with them, and finally report
answers to the correct number of significant
figures
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All non-zero numbers (1-9) are significant
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Zeros
◦ There are 3 types
 Preceding (example – 0.00235)
 Middle (example – 2002.01)
 Trailing (examples – 100.0, 100)
Which of the following has 3 significant
figures?
A. 0.003
B. 320
C. 1001.1
D. 4.0031
E. 901.0
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Multiplication and division rule
◦ Report your answer to the same number of
significant figures as the number in the problem
with the fewest significant figures
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Addition and subtraction rule
◦ Report your answer to the same column as the
number in the problem with the least precision
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Find the volume of a cube that is 3.23 cm on
each edge.
What is the sum of 67.14 kg and 8.2 kg?
A. 75 kg
B. 75.3 kg
C. 75.30 kg
D. 75.34 kg
E. 75.4 kg
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Calculate the density of a 17.982 g object
that occupies 4.13 cm3
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Numbers are written in the form:
◦ M x 10n
◦ Where M = any number >1 but < 10
 1.25, 9.8, 2
Which of the following is not correctly written
in scientific notation?
A. 1.00 x 104
B. 1.1 x 10-3
C. 0.9 x 109
D. 7 x 101
E. 2.0 x 1015
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Directly Proportional
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This means whatever one variable does the
other variable will do exactly the same
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Graphically this will result in a straight line
◦ Two quantities are directly proportional if
dividing them gives a constant value
◦ i.e. Density
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Inversely Proportional
◦ Two quantities are inversely proportional to one
another if their product is equal to a constant
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If one goes up the other will go down by a
corresponding amount
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Graphically this will result in a hyperbola
Suggested Problem Set:
Page 59 #4, 8-13, 16-18, 21-23, 27-30, 32-34, 37-45
Chapter 2 Quizzes:
Monday, Wednesday
Unit 1 Test:
Friday, August 27