Section 3.2 The International System of Units International System of Units (SI) –Revised version of metric system –We use mostly SI units in class Metric System –Based on.
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Transcript Section 3.2 The International System of Units International System of Units (SI) –Revised version of metric system –We use mostly SI units in class Metric System –Based on.
Section 3.2
The International System
of Units
International
System of Units
(SI)
–Revised version of metric system
–We use mostly SI units in class
Metric
System
–Based on 10s
–Internationally used
–EASY!
7
base units in SI measurement
–You need to know these 5 for now:
Length: meter (m)
Mass: kilogram (kg)
Time: second (s)
Quantity: mole (mol)
(6.02 x 1023)
Temperature: Kelvin (K)
Other
common units to know:
–Volume: cubic meter (m3), liter
(L), milliliter (mL)
(derived unitcomes from other SI units.)
–Temperature: Celcius (oC)
–Energy: Joule (J)
Metric
Prefixes: many, many,
many!
–Memorize these:
kilo-= 1000
centi-- = 1/100 or .01
milli-= 1/1000 or .001
Section 3.3
Conversion Problems
Conversion
Factor
–A ratio of equivalent
measurements.
Examples:
–Time…
–Money…
–Rulers…
When
using conversion factors,
the number value changes, but
the actual size of the
measurement does not…
–Change $1.00 into pennies
=
Same amount of money, but
different number value.
Equivalent measurement is…
=
Dimensional
Analysis
– An organized way to analyze and solve
problems using conversion factors.
– Carefully…AND NEATLY!
Read problem.
Set up problem with what you know
and don’t know.
Label EVERYTHING!
Calculate the number value, cancel
out units.
Evaluate: Does your answer make
sense?
Write final answer with units.
Practice Problem
If
you have Chemistry class for 85
minutes, how many seconds are you
in class?
Practice Problem
If
it took you 6 hours to drive to
Chicago, how many seconds were
you in the car?
Practice Problem
If
your bus to Chicago drove at an
average speed of 85 kilometers/hour,
what was the average speed in
meters/second?
Section 3.4
Density
Definition:
Density is the ratio of the mass of
an object to its volume.
In other words:
How much stuff is packed into a
certain amount of space.
High density
Low density
Formula:
Density =
Mass
Volume
Units:
grams
Density =
mL
Or:
g/mL
Or:
any mass units/any volume units
Density
is an intensive
property.
–It does not depend on how much
of a substance you have.
Density
is an identifying
property.
–It can be used to help identify a
substance.
Practice Problems
A
piece of metal has a mass of 3.5g
and a volume of 0.18 cm3. What is
its density?
Practice Problems
1.2
L of an unknown gas has a mass
of 1.6 g. What is its density?
What
do you think is the identity of
this gas? (see chart on p. 90)