Download Chemistry 6.2 - Conversions - Notes Teacher

Ch. 5 Notes---Scientific Measurement
Qualitative vs. Quantitative
•
Qualitative measurements give results in a descriptive nonnumeric
form. (The result of a measurement is an _____________
adjective
describing the object.)
short
heavy long, __________...
cold
*Examples: ___________,
___________,
•
Quantitative measurements give results in numeric form. (The
number
results of a measurement contain a _____________.)
600 lbs. 22 meters, __________...
5 ºC
*Examples: 4’6”, __________,
Accuracy vs. Precision
•
single measurement is to the
Accuracy is how close a ___________
true __________
value
________
of whatever is being measured.
•
several measurements are to
Precision is how close ___________
each ___________.
other
_________
Practice Problem: Describe the shots for the targets.
Bad Accuracy & Bad Precision
Good Accuracy & Bad Precision
Bad Accuracy & Good Precision
Good Accuracy & Good Precision
Significant Figures
•
Significant figures are used to determine the ______________
of a
precision
measurement. (It is a way of indicating how __________
precise a
measurement is.)
*Example: A scale may read a person’s weight as 135 lbs. Another
scale may read the person’s weight as 135.13 lbs. The ___________
second
more significant figures in the
scale is more precise. It also has ______
measurement.
•
•
•
Whenever you are measuring a value, (such as the length of an
object with a ruler), it must be recorded with the correct number of
sig. figs.
ALL the numbers of the measurement known for sure.
Record ______
Record one last digit for the measurement that is estimated. (This
reading in between the
means that you will be ________________________________
marks of the device and taking a __________
guess
__________
at what the next
number is.)
Significant Figures
•
Practice Problems: What is the length recorded to the correct
number of significant figures?
length = ________cm
11.65
(cm) 10
20
30
40
length = ________cm
58
50
60
70
80
90
100
For Example
•
•
•
Lets say you are finding the average mass of beans. You would
count how many beans you had and then find the mass of the
beans.
26 beans have a mass of 44.56 grams.
44.56 grams ÷26 =1.713846154 grams
So then what should your written answer be?
How many decimal points did you have in
your measurement?
2
Rounded answer = 1.71 grams
Rules for Counting Significant Figures in a Measurement
•
When you are given a measurement, you will need to be aware of
how many sig. figs. the value contains. (You’ll see why later on in this
chapter.)
Here is how you count the number of sig. figs. in a given measurement:
#1 (Non-Zero Rule): All digits 1-9 are significant.
3
*Examples: 2.35 g =_____S.F.
2 S.F.
2200 g = _____
#2 (Straddle Rule): Zeros between two sig. figs. are significant.
3
4
*Examples: 205 m =_____S.F.
80.04 m =_____S.F.
5
7070700 cm =_____S.F.
#3 (Righty-Righty Rule): Zeros to the right of a decimal point AND
anywhere to the right of a sig. fig. are significant.
3
3
*Examples: 2.30 sec. =_____S.F.
20.0 sec. =_____S.F.
4
0.003060 km =_____S.F.
Rules for Counting Significant Figures in a Measurement
#4 (Bar Rule): Any zeros that have a bar placed over them are sig. (This
will only be used for zeros that are not already significant because of
Rules 2 & 3.)
4
*Examples: 3,000,000 m/s =_____S.F.
2
20 lbs =____S.F.
#5 (Counting Rule): Any time the measurement is determined by
simply counting the number of objects, the value has an infinite
number of sig. figs. (This also includes any conversion factor involving
counting.)
∞
∞
*Examples: 15 students =_____S.F.
29 pencils = ____S.F.
∞
∞
7 days/week =____S.F.
60 sec/min =____S.F.
Calculations Using Sig. Figs.
•
When adding or subtracting measurements, all answers are to be
decimal __________
places
rounded off to the least # of ___________
found in
the original measurements.
Example:
+
≈ 157.17
•
(only keep 2 decimal places)
When multiplying or dividing measurements, all answers are to be
significant_________
figures found in the
rounded off to the least # of _________
original measurements.
Practice Problems:
(only keep 1
decimal place)
4.7 cm
2.83 cm + 4.009 cm − 2.1 cm = 4.739 cm ≈_____
98 m2
36.4 m x 2.7 m = 98.28 m2 ≈ _____
(only keep 2 sig. figs)
5.9 g/mL
0.52 g ÷ 0.00888 mL = 5.855855 g/mL ≈ ____
(only keep 2
sig. figs)
•
•
•
•
Mass vs. Weight
Mass depends on the amount of
___________
in the object.
matter
Weight depends on the force of
____________
acting on the object.
gravity
Weight
______________
may change as you
move from one location to another;
mass
____________
will not.
Mass = 80 kg
You have the same ____________
on
mass
the moon as on the earth, but you
weigh
___________
less since there is less
gravity on the moon.
_________
Weight = 176 lbs.
Mass = 80 kg
Weight = 29 lbs.
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The SI System (The Metric System)
Here is a list of common units of measure used in science:
Standard Metric Unit
Quantity Measured
mass
kilogram, (gram)
______________
length
meter
______________
cubic meter, (liter)
______________
volume
seconds
______________
time
temperature
Kelvin, (˚Celsius)
_____________
The following are common approximations used to convert from our
English system of units to the metric system:
1 yard
1 m ≈ _________
2.2 lbs.
1 kg ≈ _______
1.609 km ≈ 1 mile
mass of a small paper clip
1 gram ≈ ______________________
sugar cube’s volume
1mL ≈ _____________
1 L ≈ 1.06 quarts
dime
1mm ≈ thickness of a _______
The SI System (The Metric System)
•
Metric Conversions
The metric system prefixes are based on factors of _______.
mass Here is a
list of the common prefixes used in chemistry:
kilo- hecto- deka-
•
•
deci- centi- milli-
The box in the middle represents the standard unit of measure such
as grams, liters, or meters.
Moving from one prefix to another involves a factor of 10.
cm = 10 _____
dm = 1 _____
m
*Example: 1000 millimeters = 100 ____
•
The prefixes are abbreviated as follows:
k h da g, L, m d c m
grams
Liters meters
*Examples of measurements: 5 km 2 dL 27 dag 3 m 45 mm
Metric Conversions
•
To convert from one prefix to another, simply count how many places
you move on the scale above, and that is the same # of places the
decimal point will move in the same direction.
deci- centi- milliPractice Problems: kilo- hecto- deka380,000
0.00145
380 km = ______________m
1.45 mm = _________m
461 mL = ____________dL
4.61
0.4 cg = ____________
0.0004
dag
0.26 g =_____________
mg
230,000 m = _______km
260
230
Other Metric Equivalents
1 mL = 1 cm3
1 L = 1 dm3
For water only:
1 L = 1 dm3 = 1 kg of water or 1 mL = 1 cm3 = 1 g of water
Practice Problems:
0.3 L
(1) How many liters of water are there in 300 cm3 ? ___________
50 kg
(2) How many kg of water are there in 500 dL? _____________
Metric Volume: Cubic Meter (m3)
10 cm x 10 cm x 10 cm = Liter
Ch. 4 Problem Solving in Chemistry
Dimensional Analysis
conversion
• Used in _______________
problems.
*Example: How many seconds are there in 3 weeks?
• A method of keeping track of the_____________.
units
Conversion Factor
ratio of units that are _________________
equivalent
• A ________
to one another.
*Examples:
1 min/ ___
60 sec (or ___
60 sec/ 1 min)
7 days/ 1 week (or 1 week/ ___
7 days)
___
1000 m/ ___
1 km
(or ___
1 km/ 1000 m)
• Conversion factors need to be set up so that when multiplied, the unit
of the “Given” cancel out and you are left with the “Unknown” unit.
top and the
• In other words, the “Unknown” unit will go on _____
“Given” unit will go on the ___________
bottom
of the ratio.
How to Use Dimensional Analysis to Solve Conversion Problems
• Step 1:
Identify the “________”.
Given
This is typically the only number
given in the problem. This is your starting point. Write it down! Then
write “x _________”. This will be the first conversion factor ratio.
• Step 2:
Identify the “____________”.
This is what are you trying to
Unknown
figure out.
• Step 3:
Identify the ____________
Sometimes you will
conversion _________.
factors
simply be given them in the problem ahead of time.
• Step 4:
By using these conversion factors, begin planning a solution
to convert from the given to the unknown.
• Step 5:
When your conversion factors are set up, __________
multiply all the
divide
numbers on top of your ratios, and ____________
by all the numbers
on bottom.
If your units did not ________
cancel ______
out correctly, you’ve messed up!
Practice Problems:
(1)How many hours are there in 3.25 days?
3.25 days x 24 hrs = 78 hrs
1 day
(2) How many yards are there in 504 inches?
504 in. x 1 ft
12 in.
x 1 yard
3 ft
= 14 yards
(3) How many days are there in 26,748 seconds?
26,748 sec x 1 min x 1 hr x 1 day
60 sec 60 min
24 hrs
= 0.30958 days
Converting Complex Units
• A complex unit is a measurement with a unit in the _____________
numerator
and ______________.
denominator
*Example: 55 miles/hour 17 meters/sec 18 g/mL
• To convert complex units, simply follow the same procedure as
top first. Then convert the
before by converting the units on ______
bottom
units on __________
next.
Practice Problems: (1) The speed of sound is about 330 meters/sec.
What is the speed of sound in units of miles/hour? (1609 m = 1 mile)
330m x 1 mile x 3600 sec = 738 miles/hr
sec
1609 m
1 hr
(2) The density of water is 1.0 g/mL. What is the density of water in
units of lbs/gallon? (2.2 lbs = 1 kg) (3.78 L = 1 gal)
1.0 g x 1 kg x 2.2 lbs x 1000 mL x 3.78 L = 8.3 lbs/gal
mL
1000 g
1 kg
1L
1 gal