Download Measure in Chemistry

Metric System
Essential Questions: What is the metric system?
Why is the metric system advantageous over the
English system?
Metric System:
 Also known as the SI (International System of
Units)
 Based on units that are multiples of 10
 5 basic units most commonly used by chemists:
 Meter
 Kilogram
 Kelvin
 Second
 Mole
• Uses prefixes to change the value of units
PREFIX
SYMBOL
VALUE
Mega
M
1,000,000
Kilo
k
1000
Deci
d
0.1
Centi
c
0.01
Milli
m
0.001
Micro
u
0.000001
Nano
n
0.0000000001
Lengths
• Meter is the basic unit of length
• Other commonly use units of length are
cm, mm, and km
• 1m = 10dm = 100cm = 1,000mm
Table C and Table D
UNIT
Kilometer (km)
RLATIONSHIP
1km = 103 m
EXAMPLE
Length of about 5
city blocks
Meter (m)
Base unit
Height of
doorknob from the
floor
Decimeter (dm)
101dm =1 m
Diameter of large
orange
Centimeter (cm)
102 cm = 1m
Millimeter (mm)
103 mm=1m
Micrometer (um)
106 um = 1mm
Width of a shirt
button
Thickness of a
dime
Diameter of
bacterial cell
Thickness of RNA
molecule
Nanometer (nm)
109 nm = 1mm
Volume
Space occupied by a sample of
matter
Base unit is the liter (L ).
Other commonly use units of volume
are liter, milliliter, cubic centimeter
and micro liter
UNIT
RELATIONSHIP
EXAMPLE
Liter (L)
Base unit
Quart of milk
Milliliter (ml)
103 = 1 Liter
20 drops of
water
Cube of sugar
Cubic centimeter 1 cm3 – 1 ml
(cm3)
Micro liter (um) 106 n L- 1L
Crystal of table
salt
Mass
 Base unit is kilogram
 Common used metric units include liter,
milliliter, cubic centimeter and
micrometer.
Kilogram-mass of 1 L of liquid water at 4C.
Weight- force of the pull of gravity on an
object.
UNIT
REALTIONSHIP
EXAMPLE
Kilogram (km)base unit
1 kg = 103 g
Small textbook
Gram (g)
1 g = 10-3 kg
Dollar bill
Milligram (mg)
103 mg =1 g
Ten grains of salt
Microgram (ug) 106 ug = 1 g
Particle of baking
powder
Temperature
• Measure of how or cold an object is.
• Base unit is Kelvin (k).
• Commonly used units include Celsius and
Kelvin
K=C + 273
C = K-273
Table T
Energy





The capacity to do work
Base unit is the joule (J).
Commonly used units include joule and
calorie.
1 J = .2390 cal
1 cal = 4.184 J
Metric Problems
Solve the following:
1 Km = ________m
1 cm = ________m
1 mg = ________g
1 ml = ________L
1 m = _________mm
1 cm3 = _________ ml
Write the correct prefix for the
following measurements:
1000 g = _________kg
0.001 m =________mm
Which is the larger unit?
cm or dm
ul or ml
Essential Question: What is scientific notation?
• Scientific notation takes the form of M
x 10n.
• n represents the number of decimal
places to be moved.
Ex. 84,000 = 8.4 x 104
= 8.4 x 10 x10 x 10 x 10
• A positive n represents a lager number.
• Very large and very small numbers are
often expresssed in scientific notation.
A negative n number represents a number
between zero and 1.
Ex. 0.00025= 2.5 x 10-4
2.5 x 10 -4 = _____2.5__________
10 x 10 x 10 x 10
Scientific Notation Problems:
500 = __________
.025 =__________
.0008 =__________
1,000,000 = ________
1.5 x 103 =___________
1 x10-1 = ___________
3.75 x 10-2 = _________
4 x 100 = ___________
Multiplication and Division
To multiply numbers written in scientific notation,
multiply the coefficients and add the
exponents.
Exs: ( 2.1 x 103)x (4.0 x 10-7)=
(2.1 x 4.0) + 103+(-7) = 8.4 x 10-4
3.0 x 105 =
6.0 x 102
3.0 x 105-2=
6.0
0.5x 103 = 5.0 x10
2
Addition and Subtraction
To add or subtract the exponent needs to be the
same.
Exs:
5.4 x103 + 8.0 x 102=
5.4 x103 + .80 x 103=
(5.4 + .80) x 103= 6.2 x 103
(3.42 x 10 -5) – (2.5 x 10-6) =
(3.42 x 10 -5) – (.25 x 10-5) =
(3.42-.25) x 10-5 = 3.17 x 103

Essential Questions: What is dimensional
Analysis? What are conversion factors? How are
the two related?
• Way to analyze and solve problems using
the units, or dimensions, of the
measurements.
• Uses conversion factors.
Conversion Factor- ratio of equivalent
measurements
1 dollar= 4 quarters=10 dimes=20
nickels=100 pennies
1m = 10dm=100cm= 1,000m
Dimensional Analysis Problems
How many liters are in 5 L?
a. List the known and unknowns:
Known:
Unknown
5L
ml=?
1 L= 1000ml
b. Solve:
5 L x 1,000ml = 5000 ml or 5 x 10 3 ml
1L
How many seconds are in a workday that lasts
exactly eight hours?
a. List known and unknowns.
Known:
Unknown:
Time worked =8 h
second worked
1h=60 min
1 min=60 s
b. Solve :
8 h x 60 min x 60 sec =28,800s or 2.8800 x
1h
1 min
104s
Water runs through a hose at the rate of 2.5
gal/min/ What is the rate of water flow in
gallons/day?
2.5 gal x 60 min x 24 h = 3.6 x 103 gal/day
1min
1h
1 day
Essential questions:
What is density? What is the formula for density?
Ratio of the mass of an object to its
volume.
Density (D =) =mass (m)
volume (v)



Depends on the composition of a
substance, not its size
Decreases as temperature increases.
A cooper penny has a mass of 3.1 g and a
volume of 0.35cm3. What is the density
of copper (Cu)?
D=m
v
D= .3g
0.35cm3
=8.8571g/cm3
=8.9g/cm3 (rounded to 2 sig. figs.)
Significant figures
Significant figuresmeasurement of all
the digits that are
known, plus a last
digit that is estimated
Rules for Determining significant
figures
1. All nonzero digits are significant
ex: 2.75 - 3 sig. figs
ex: 1846 – 4 sig. figs
2. Zero located between nonzero numbers are significant
ex: 81307 – 5 sig figs
ex: 208.92 – 5 sig figs
3. Trailing zeroes in a number are significant only if the
number contains a decimal point
ex: 203.0 - 4 sig figs
ex: 1000 – 1 sig figs
ex: 10.00 – 4 sig figs
Rules for Determining significant
figures cont.
4. Zeroes at the beginning of a number
whose only function is to place the
decimal are NOT significant
ex: .0082 – 2 sig figs
ex: .00820 – 3 sig figs
ex: 0.0380 – 3 sig figs
Subtraction and addition with sig
figs.
.When adding or subtracting-limit and round your
answer to least decimal places in any number
that makes up your answer.
Exs. 8.11 L
+2.476 L
10.586L
Final answer : 10.59 L
More Examples of addition and
subtraction with sig figs
Exs. 89.23 m
4.01 m
+6.8 m
99.32 m
Final answer 99.3 m
8.63 L
-7.0 L
1.63 L
Final answer 1.6 L
Multiplication and division with sig
figs.
► When
multiplying and
dividing, limit and
round to the least
number of sig figs.
► Ex: 7.55 m X .34 m =
2.567 m2 = 2.6 m2 (2
sig figs)
Essential Questions: What is percent
error? How do you calculate percent
error?
Accepted Value-correct value based on
reliable references
Measured Value (experimental value)-the
value measured in the lab.
Error=experimental value-accepted value
Percent error =
measured value - accepted value x 100
accepted value
What is the percent error for a student who
actual weight is 107 lbs, but when she
steps on the scale is weights 114 lbs?
Let’s assume the scale is incorrect and that
she is not eating too many Big Macs!
=114lbs-107 lbs
107lbs
=7%
Table T