Transcript units of measurement

UNITS OF
MEASUREMENT
The metric system
CHEMISTRY
You
will be studying chemistry
Chemistry is defines as “the
study of matter and its
reactions”
Chemistry is a physical science
so we need to discuss how we
measure things
WHAT ARE UNITS OF
MEASUREMENT?
 Units
describe what aspect of matter is
being measured
 Qualitative: something that is described
 Quantitative: something that is
measured
 Examples:
 Unit of distance – mile
 Unit of volume – gallon
 Unit of time – hour
 Unit of weight - pound
SI UNITS OF MEASUREMENT
 SI
– Standards International
 Set of units that are recognized by
the scientific community
 In science (unlike math), you need
a unit for EVERY NUMBER
 These are the units we will be using
in this class – not English units
BASE UNIT
 Metric
system is a base 10 system
A
base unit is a unit that measures some
sort of physical/chemical data
 Distance
– meter (m)
 Mass – gram (g)
 Volume – liter (L)
 Time – second (s)
 Temperature – degrees Celsius (°C)
 Energy – Joules (J)
MASS – A QUICK EXPLANATION



Mass and weight are different
Weight can change. It is not an absolute
value
 Weight depends upon the force of gravity
 You weigh more on Earth than on the Moon
Mass cannot change. It is an absolute value
 Mass depends on the amount of matter in
a substance
 Mass does not change with gravity
PREFIXES (GET HANDOUT)



Look at the name of the prefixes and the
abbreviation on the sheet
These prefixes work for all base units
The prefix tells you how the base unit can be
changed
 Example:
 If you have a cg (centigrams), this means
that the centigram is 1/100 of a gram.
 If you have a cL (centiliter), this means
that the centiliter is 1/100 of a liter.
HOW DO WE CHANGE THE
BASE UNIT?
 How
big the measurement is depends on
the prefix from the metric system
 You increase or decrease the size of the
number by changing the prefix in front of
the base unit
 IMPORTANT
NOTE:
 When you go DOWN the chart, the
number gets BIGGER
 When you go UP the chart, the number
gets SMALLER
STEPS TO CONVERT : EXAMPLE:
100mm = _?_cm
Step 1: Find the conversion on the last column of the
handout (Look at the prefixes)
 100mm = _____ cm
 m (milli):
1 meter = 1000 mm
 c (centi): 1 meter =100 cm
Step 2: Use the conversion from the last column to convert to
the base unit. (We will use ratios)
We start with 100millimiters (mm) and we
want to make it the base unit meters (m)



The base unit DOES NOT have a prefix
Therefore: 100 mm = ??? m
MATH FOR THE STEP 2
 We
look at the prefix conversion from the
first step





1m = 1000mm
We start with 100mm
So the equation is:
1m____ =
(x) m____
1000mm
100mm
Solve for x to find the number of meters
NOTE: The meters(m) are both on top and
the millimeters(mm)are both on bottom
ANSWER FOR STEP 2
 When
you cross-multiply, you get the
following:
x = 0.1m
STEPS TO CONVERT
Step 3: Use the answer that you got from step 2,
to calculate into the unit you are looking for
(cm)
 We have our answer from step 2 (0.1m)
 We want to convert it to our second unit
(cm)
 Therefore, we want to turn 0.1m into
centimeters (cm)
 We will use the other conversion from the
first step

1meter (m) = 100 centimeters (cm)
MATH FOR STEP 3





1m = 100cm
We start with 0.1m
So the equation is:
1m____ =
0.1 m____
100cm
(x) cm
Solve for x to find the number of
centimeters
NOTE: The meters(m) are both on top and
the centimeters (cm) are both on bottom
ANSWER FOR STEP 3

When you cross-multiply, you get the
following:
x = 10 cm

NOTE: I know most of you know how to move
the decimal to get the answer. YOU have to
do it this way for the homework and quizzes.
THERE IS A REASON.
ONE FINAL THING
 The
example we just did showed how to
go from to numbers with prefixes in their
units mm to cm

This process involved 2 math steps
 If
your problem only has 1 number with a
prefix, you will only need 1 math step


Example:
250 cm = ??? m
MATH FOR EXAMPLE
100 cm = ??? m

Find the value in the final column for
centimeters (cm)
 1meter

(m) = 100 centimeters (cm)
Set up the ratio:
1m__ = (x) m__
100 cm

x = 2.5m
250 cm
PRACTICE
1.
Try the following 3 conversions IN YOUR
NOTES:
1500 g = __?__ kg
2.
63.3 hL = __?__ mL
3.
1.22 km = __?__ nm

ANSWERS
1.
1.500 g
2.
6,330,000 mL
3.
1,220,000,000,000 nm
TRY THESE IN ON YOUR OWN
1.
2.
3.
4.
5.
6.
7.
0.25 hg =
3200 cm =
0.0036 kL =
33400nJ =
225 dkg =
880 hm =
1 nL
=
________ g
________ m
________ mL
_______ kJ
________ dg
________ um
________ kL
SCIENTIFIC NOTATION
 Some
numbers are so big or small that you
have to write too many numbers
 Scientists have a short hand way to
abbreviate these number called scientific
notation
 Let’s look at the current national debt
13,600,000,000,000
dollars
FORMAT

1.
In scientific notation we use exponents
to tell us how to move the decimal
Write the number (without any zeroes
before or after it)

2.
136
Put a decimal after the first digit

1.36
FORMAT
3.
Count how many spaces before
or after the decimal that you
need to move the decimal to get
to your original number



1.36
13,600,000,000,000.
You have to move the decimal 13
spaces to the right
FORMAT
4.
Use the following convention that
shows you moved the decimal 13
spaces

5.
x 1013
Put the original number from step
2 with step 4


1.36 x 1013
This tells you to move the decimal 13
places to the right
QUESTION
How
do you show that we
move the decimal to the left?
For example:
0.00122
ANSWER
 Same
method except you use a
negative (-) number in the exponent
to show that the decimal goes to the
left
 1.22
x 10-3
 The (-)3 says to move the decimal 3
spots to the left in the number 1.22
TRY THESE
1.
What are the following numbers in
scientific notation?
1.
2.
356,000,000
0.0000125
2.
What are the following numbers written
out as a numeral?
1.
2.
2.50 x 102
7.77 x 10-3
ANSWER
1.
2.
What are the following numbers in
scientific notation?
1. 3.56 x 108
2. 1.25 x 10-5
What are the following numbers
written out as a numeral?
1. 250
2. 0.00777
PRACTICE WITH CALCULATORS
 You
will need to know how to read
and enter scientific notation on
calculators
 After
receiving a calculator, we will
practice some on the board.