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Section 2: Scientific Notation and Dimensional Analysis
Scientists use scientific methods to systematically pose and test
solutions to questions and assess the results of the tests.
K
What I Know
W
What I Want to Find Out
L
What I Learned
• 2(G) Express and manipulate chemical quantities using
scientific conventions and mathematical procedures, including
dimensional analysis, scientific notation, and significant figures.
• 2(H) Organize, analyze, evaluate, make inferences, and predict
trends from data.
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Scientific Notation and Dimensional Analysis
Essential Questions
• Why use scientific notation to express numbers?
• How is dimensional analysis used for unit conversion?
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Scientific Notation and Dimensional Analysis
Vocabulary
Review
New
• quantitative data
• scientific notation
• dimensional analysis
• conversion factor
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Scientific Notation and Dimensional Analysis
Scientific Notation
Scientific notation can be used to express any number as a number between 1
and 10 (known as the coefficient) multiplied by 10 raised to a power (known as
the exponent).
• Carbon atoms in the Hope Diamond = 4.6 x 1023
• 4.6 is the coefficient and 23 is the exponent.
Count the number of places the decimal point must be moved to give a
coefficient between 1 and 10. The number of places moved equals the value of
the exponent. The exponent is positive when the decimal moves to the left and
negative when the decimal moves to the right.
• 800 = 8.0 × 102
• 0.0000343 = 3.43 × 10–5
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Scientific Notation and Dimensional Analysis
Scientific Notation
Addition and subtraction
• Exponents must be the same.
• Rewrite values to make exponents the same.
• Example: 2.840 x 1018 + 3.60 x 1017, you must rewrite one of these
numbers so their exponents are the same. Remember that moving the
decimal to the right or left changes the exponent.
• 2.840 x 1018 + 0.360 x 1018
• Add or subtract coefficients.
• Ex. 2.840 x 1018 + 0.360 x 1018 = 3.2 x 1018
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Scientific Notation and Dimensional Analysis
SCIENTIFIC NOTATION
SOLVE FOR THE UNKNOWN
Use with Example Problem 2.
Problem
Write the following data in scientific notation.
Move the decimal point to give a coefficient
between 1 and 10. Count the number of places
the decimal point moves, and note the direction.
•
Move the decimal point six places to the left.
•
Move the decimal point eight places to the
right.
•
Write the coefficients, and multiply them by
10n where n equals the number of places
moved. When the decimal point moves to the
left, n is positive; when the decimal point
moves to the right, n is negative. Add units to
the answers.
a. The diameter of the Sun is 1,392,000 km.
b. The density of the Sun’s lower atmosphere
is 0.000000028 g/cm3 .
Response
ANALYZE THE PROBLEM
You are given two values, one much larger than 1
and the other much smaller than 1. In both cases,
the answers will have a coefficient between 1 and
10 multiplied by a power of 10.
a. 1.392 × 106 km
b. 2.8 × 10-8 g/cm3
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Scientific Notation and Dimensional Analysis
SCIENTIFIC NOTATION
EVALUATE THE ANSWER
The answers are correctly written as a
coefficient between 1 and 10 multiplied by
a power of 10. Because the diameter of
the Sun is a number greater than 1, its
exponent is positive. Because the density
of the Sun’s lower atmosphere is a
umber less than 1, its exponent is
negative.
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Scientific Notation and Dimensional Analysis
Scientific Notation
Multiplication and division
• To multiply, multiply the coefficients, then add the exponents.
– Example: (4.6 x 1023)(2 x 10-23) = 9.2 x 100
• To divide, divide the coefficients, then subtract the exponent of the divisor
from the exponent of the dividend.
– Example: (9 x 107) ÷ (3 x 10-3) = 3 x 1010
• Note: Any number raised to a power of 0 is equal to 1: thus, 9.2 x 100 is equal
to 9.2.
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Scientific Notation and Dimensional Analysis
MULTIPLYING AND DIVIDING NUMBERS IN SCIENTIFIC NOTATION
SOLVE FOR THE UNKNOWN
Use with Example Problem 3.
Problem A:
Problem
•
Solve the following problems.
a. (2 × 103) × (3 × 102)
b. (9 × 108) ÷ (3 × 10-4)
State the problem.
a. (2 × 103) × (3 × 102)
•
Multiply the coefficients.
2×3=6
•
Add the exponents.
Response
ANALYZE THE PROBLEM
You are given numbers written in scientific notation
to multiply and divide. For the multiplication
problem, multiply the coefficients and add the
exponents. For the division problem, divide the
coefficients and subtract the exponent of the divisor
from the exponent of the dividend.
9 × 108
In this equation, the exponent of the
3 × 10−4
dividend is 8. The exponent of the divisor is −4.
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3+2=5
•
Combine the parts.
6 × 105
Problem B:
•
State the problem.
b. (9 × 108) ÷ (3 × 10-4)
•
Divide the coefficients.
9÷3=3
Scientific Notation and Dimensional Analysis
MULTIPLYING AND DIVIDING NUMBERS IN SCIENTIFIC NOTATION
SOLVE FOR THE UNKNOWN
Problem B continued:
•
Subtract the exponents.
EVALUATE THE ANSWER
To test the answers, write out the original
data and carry out the arithmetic. For
example, Problem a becomes 2000 × 300
= 600,000, which is the same as 6 × 105.
8 − (−4) = 8 + 4 = 12
•
Combine the parts.
3 × 1012
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Scientific Notation and Dimensional Analysis
Dimensional Analysis
Dimensional analysis is a systematic approach to problem solving that uses
conversion factors to move, or convert, from one unit to another. A conversion
factor is a ratio of equivalent values having different units.
Writing conversion factors:
• Conversion factors are derived from equality relationships, such as 1 dozen
eggs = 12 eggs.
• Percentages can also be used as conversion factors. They relate the number
of parts of one component to 100 total parts.
Using conversion factors:
• A conversion factor must cancel one unit and introduce a new one.
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Scientific Notation and Dimensional Analysis
USING CONVERSION FACTORS
Use with Example Problem 4.
KNOWN
UNKNOWN
Length = 6 Egyptian cubits
length= ? g
Problem
7 palms = 1 cubit
In ancient Egypt, small distances were
measured in Egyptian cubits. An
Egyptian cubit was equal to 7 palms,
and 1 palm was equal to 4 fingers. If 1
finger was equal to 18.75 mm, convert
6 Egyptian cubits to meters.
1 palm = 4 fingers
Response
cubits → palms → fingers → millimeters → meters
ANALYZE THE PROBLEM
A length of 6 Egyptian cubits needs to be
converted to meters.
•
1 finger = 18.75 mm
1 m = 1000 mm
SOLVE FOR THE UNKNOWN
Use dimensional analysis to convert the units
in the following order.
Multiply by a series of conversion factors
that cancels all the units except meter, the
desired unit.
6 cubits ×
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7 palms
1 cubit
×
4 fingers
1 palm
×
18.75 mm
1 finger
1 meter
×
1000 mm
=?m
Scientific Notation and Dimensional Analysis
USING CONVERSION FACTORS
SOLVE FOR THE UNKNOWN
6 cubits ×
7 palms
1 cubit
×
4 fingers
1 palm
×
18.75 mm
1 finger
1 meter
= 3.150
1000 mm
×
m
EVALUATE THE ANSWER
Each conversion factor is a correct
restatement of the original relationship,
and all units except for the desired unit,
meters, cancel.
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Scientific Notation and Dimensional Analysis
Review
Essential Questions
• Why use scientific notation to express numbers?
• How is dimensional analysis used for unit conversion?
Vocabulary
• scientific notation
Copyright © McGraw-Hill Education
• dimensional
analysis
• conversion factor
Scientific Notation and Dimensional Analysis