Transcript Chapter 1

CHEM 205
Tutorial 0
chapter 1
http://www.karentimberlake.com/chemodul.htm
Units of measurement
Measurement
You are making a measurement when you
 Check you weight
 Read your watch
 Take your temperature
 Weigh an apple
What kinds of measurements did you make today?
Some Tools for Measurement
How do you
measure….
Temperature?
Time?
Volume?
Weight?
Measurement in Science
In Science we
do experiments
measure quantities
use numbers to report measurements
Units in the Metric System (S.I.)

length
meter
m

volume
liter
L

mass
gram
g

temperature
Celsius
°C
Stating a Measurement
In every measurement there is a
NUMBER followed by
a UNIT from measuring device
The patient’s temperature is 102°F.
The sack holds 5 lbs of potatoes.
It is 8 miles from your house to school.
The bottle holds 2 L of orange soda
Significant Figures
Reading a measure
First digit (known)
=2
2.?? cm
Second digit (known)
= 0.7
2.7? cm
Third digit (estimated) between 0.05- 0.07
Length reported
=
2.74 cm
or
2.75 cm
or
2.73 cm
Known, significant, estimated digits
2.74 cm
Significant!
Known
(100% certain)
Estimated
(uncertain)
What is the length of the line?
l5. . . . I . . . . I6. . . .I . . . . I7. .
1) 6.0 cm
2) 6.06 cm
3) 6.60 cm
cm
Exact Numbers
 Obtained when you count objects
2 soccer balls
1 watch
3 pizzas
 Obtained from a defined relationship
1 foot = 12 inches
1 meters = 100 cm
 Not obtained with measuring tools
Classify each of the following as
an exact (E) or a measured (M)
number.
A._M_Goldmelts
A.___Gold
meltsat
at1064°C
1064°C
B._E_1 yard
B.___1
yard == 33 feet
feet
C._M_Ared
C.___A
redblood
bloodcell
cellwith
withdiameter
diameter66xx10
10-4-4cm
cm
D._E_There were
D.___There
were 66 hats
hats on
on the
the shelf
shelf
E._M_Acan
E.___A
canof
ofsoda
sodacontains
contains355
355mL
mLof
ofsoda
soda
Significant Figures in
Calculations
Counting Significant Figures
Number of Significant Figures
38.15 cm
0.008 ft
25000 in
0.48600 gal
4
1
2
5
Significant Numbers in Calculations
 A calculated answer cannot be more precise than
the measuring tool.
 Significant figures are needed for final answers
from
1) adding or subtracting
2) multiplying or dividing
Adding and Subtracting
The answer has the same number of
decimal places as the measurement with
the fewest decimal places.
25.2
ONE decimal place
+ 1.34 TWO decimal places
26.54
answer 26.5 ONE decimal place
In each calculation, round the answer to
the correct number of significant
figures.
A. 235.05 + 19.6 + 2.1 =
1) 256.75
2) 256.8
B.
58.925 - 18.2 =
1) 40.725
2) 40.73
3) 257
3) 40.7
Multiplying and Dividing
Round (or add zeros) to the calculated
answer until you have the same number
of significant figures as the measurement
with the fewest significant figures.
In each calculation, round the answer
to the correct number of significant
figures.
A. 2.19 X 4.2 =
1) 9
B.
C.
4.311 ÷ 0.07 =
1) 61.58
2.54 X 0.0028
0.0105 X 0.060
1) 11.3
2) 9.2
3) 9.198
2) 62
3) 60
=
2) 11
3) 0.041
Prefixes and
Equalities
Metric Prefixes
 Increase or decrease basic unit by 10
 Form new units larger or smaller than the
basic units
0.00356 = 3.56 x 10-3
123 000 000 000 000 = 123 x 1012
Prefix Symbol
giga
G
mega
M
kilo
k
hecto
h
deca
da
no prefix means:
deci
d
centi
c
milli
m
micro
m
nano
n
Value
Exponential
1,000,000,000
109
1,000,000
1,000
100
10
1
0.1
0.01
0.001
0.000001
0.000000001
106
103
102
101
100
10-1
10-2
10-3
10-6
10-9
Give the value of the following units:
A. 1 kg = ____ g
1) 10 g
2) 100 g
3) 1000 g
B. 1 mm = ____ m
1) 0.001 m 2) 0.01 m
3) 0.1 m
Equalities
State the same measurement in two
different units
length
10.0 in.
25.4 cm
Conversion Factors
Express an equality between two different
units
Example:
1 in = 2.54 cm
Factors: 1 in
and
2.54 cm
3 in → ? cm
2.54 cm
1 in
2.54cm
8 cm
3 in x
= 7.62
1in
Blood has a density of 0.05 g/mL. If a
person lost 0.30 pints of blood at
18°C, how many ounces of blood
would that be?
Initial unit = pints
Final unit = oz
1 US pint = 16 US fluid ounces
16 oz
0.30 pints
 4.8 oz
1pint
How many seconds are in 14 days?
14 day
x 1 day
24 h
x
60 min
1h
x 60 s
1 min
14 day x 24 h x 60 min x 60 s
1 day
1h
1 min
= 1.2 x 105 s
Steps to solve a problem


READ problem

Write down a unit plan
IDENTIFY data
from the INITIAL UNIT to the DESIRED UNIT



Select CONVERSION factors


Do math on CALCULATOR (is the result logical?)
Change initial unit to desired unit
CANCEL units and check
Give an answer using SIGNIFICANT FIGURES
Measuring Temperature
Kelvin Scale
0 K is the lowest temperature
0 K = - 273°C
K
K =
°C + 273
°C
°C =
K - 273
37°C to K?
298K to °C ?
K
°C
= °C + 273 =
= 37°C + 273 =
= 310 K
= K - 273 =
= 298 - 273 =
= 25 °C
Density
Density
Density compares the mass of an
object to its volume
mass
g
g
d


v olume mL cm3
Note: 1 mL = 1 cm3
What is the density (g/cm3) of 48 g of a metal if
the metal raises the level of water in a
graduated cylinder from 25 mL to 33 mL?
1) 0.2 g/ cm3
25
mL
2) 6 g/cm3
33
mL
3) 252 g/cm3
What is the density (g/cm3) of 48 g of a metal if
the metal raises the level of water in a
graduated cylinder from 25 mL to 33 mL?
Volume (mL) of water displaced
= 33 mL - 25 mL
= 8 mL
Volume of metal (cm3)
= 8 mL x 1 cm3 =
1 mL
8 cm3
Density of metal =
mass = 48 g
= 6 g/cm3
volume
8 cm3
Solution: 6 g/cm3 (#2)
Which diagram represents the liquid layers in
the cylinder?
(K) Karo syrup (1.4 g/mL)
(V) vegetable oil (0.91 g/mL)
(W) water (1.0 g/mL)
V
W
K
1
W
K
K
V
V
W
2
3
Density as Conversion Factor
A substance has a density of 3.8 g/mL.
Density
Equality
= 3.8 g/mL
3.8 g = 1 mL = 1 cm3
Conversion factors:
3.8 g
1m L
or
1m L
3.8 g
The density of octane, a component of
gasoline, is 0.702 g/mL. What is the
mass, in kg, of 875 mL of octane?
1) 0.614 kg
2) 614 kg
3) 1.25 kg
The density of octane, a component of
gasoline, is 0.702 g/mL. What is the
mass, in kg, of 875 mL of octane?
Unit plan: mL  g  kg
Equalities: 1 mL = 0.702 g
and 1 kg = 1000 g
Calculation:
875 mL x 0.702 g
1 mL
x
Solution: 0.614 kg (#1)
1 kg
1000 g
= 0.614 kg