Download Chemistry - Orangefield ISD

Chemistry
Chapter 2
Units of Measurement
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SI Units
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Base Units
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The updated metric system
Based on factors of ten
Time - second
Length - meter
Mass – kilogram
Derived Units – combination of base units
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Volume – space occupied by an object
Density – mass per unit volume
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Density= mass/volume
Temperature
Scientific Notation and Dimensional
Analysis
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Scientific Notation
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Expresses numbers as multiple of two factors
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Example: 6.02x1023
Adding/subtracting – FIRST thing you must do is make sure
exponents are the same
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#1 – number between 1 and 10; #2 – ten raised to a power
Example: 15.6x106 + 0.165x108 = ?
1.56x107 + 1.65x107 = 3.21x107
Multiplying/dividing – also a two-step process
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Multiplying - #1 – multiply first factors; #2 add exponents
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Example: (2x103) x (3x102) = 6x105
Dividing - #1 – divide first factors; #2 subtract divisor exponent from
dividend exponent
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Example: (9x108) / (3x10-4) = 3x1012
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Dimensional analysis – problem-solving method that
focuses on units
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Conversion factors
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Ratio of equivalent values
Used to express different units
Used when you need to change units
How reliable are measurements?
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Accuracy – how close a measured value is to an accepted
value
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Precision – how close a series of measurements are to
one another
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How repeatable it is
Percent error – ratio of error to accepted value
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How “right” it is
%error = error/accepted value x 100
Significant figures – include all known digits plus one
estimated digit
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Non-zero numbers are ALWAYS significant
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Example: 72.3 has three
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Zeros between non-zero numbers are ALWAYS significant
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All final zeros to the right of the decimal place are significant
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6.20 has three
Zeros that act as placeholders are NOT significant; convert to
scientific notation to remove the placeholder zeros
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60.5 has three
0.0253 and 4320 each have three
Counting numbers and defined constants have an infinite
number of significant figures
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6 desks
60 s = 1 min
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Rounding
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Addition/subtraction
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Answer should have no more sig figs than the data with the
fewest sig figs
Rules
Answer must have same number of digits to right of decimal as
value with fewest digits to right of decimal
Line up decimals, then perform the math
Multiplication/division
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Answer must have same number of sig figs as measurement
with fewest sig figs
Representing Data
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Graphing
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Circle (pie) graph – shows parts of a whole
Bar graph – shows how a quantity varies with factors such as
time, etc.
Line graph – points represent intersection of data for 2
variables
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Independent variable on x-axis; dependent variable on y-axis
If best fit line is straight (linear) – directly related
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Line rises to right – positive slope
Line sinks to right – negative slope
Slope = (y2 – y1)/(x2 – x1)
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Interpreting graphs
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Interpolation – educated guess of data that falls between
measured points on a line graph
Extrapolation – extending the line beyond the plotted points
and estimating values for variables