Transcript Lecture Notes

Chapter Two
Measurements
In Chemistry
Measurements in Chemistry
Measurements answer questions such as
How Much?
How Long?
How Many?
Measurements have 2 parts:
___________ ______________
Chapter 2 | Slide 2
Measurements in Chemistry
Importance of Units
Job Offer: Annual Salary = 1,000,000.
Do you Accept or Reject?
Chapter 2 | Slide 3
Measurements in Chemistry
Systems of Measurement
English System
Common measurements
Pints, quarts, gallons, pounds, miles, etc.
Metric System
Units in the metric system consist of a _______ unit plus a
_________ (factor of ____).
Chapter 2 | Slide 4
Measurements in Chemistry
Base Units in the Metric System
Length
____________
Volume
____________
Mass
(measure of the total quantity of matter in an
object)
____________
Chapter 2 | Slide 5
Measurements in Chemistry cont’d
Fig. 2.2
Comparisons of
the base metric
system units of
length, mass,
and volume with
common objects.
E.R. Degginger
Chapter 2 | Slide 6
Measurements in Chemistry cont’d
Table 2.1 Prefixes
Chapter 2 | Slide 7
Measurements in Chemistry cont’d
Fig. 2.1
Metric system units are
becoming increasingly
evident on highway
signs.
David Frazier/Photo Researchers
Chapter 2 | Slide 8
Measurements in Chemistry cont’d
Fig. 2.3
A cube 10 cm on a side
is equal to 1 L; a cube
1 cm on a side is equal
to 1 mL.
Chapter 2 | Slide 9
Measurements in Chemistry cont’d
Fig. 2.4
The use of the
concentration
unit milligrams
per deciliteris
common in
clinical
laboratory
reports dealing
with the
composition of
human body
fluids.
Chapter 2 | Slide 10
Measurements in Chemistry
→ CO 2.1
Measurements are made
relative to a __________.
Measurements can never
be __________; there is
always some
______________.
© Richard Hamilton Smith/Corbis Outline
Chapter 2 | Slide 11
Measurements in Chemistry
Exact and Inexact Numbers
Exact numbers
Have no ________________ associated with them
They are known __________ because they are ________
Example: ____ inches = ___ foot
Inexact number
Have some _________________ associated with them
Example: all __________________
Chapter 2 | Slide 12
Measurements in Chemistry
Uncertainty in Measurements depends upon the
___________________ device.
All numbers you “________” (_________) from the marks
on the measuring device plus _____ “____________” or
“____________________” number (decimal place)
Chapter 2 | Slide 13
Measurements in Chemistry cont’d
Fig 2.5
The scale on a measuring
device determines the
magnitude of the uncertainty
for the recorded
measurement.
Ruler A:
3.7 contains _____ significant
digits
Ruler B:
3.74 contains _____ significant
digits
Chapter 2 | Slide 14
Measurements in Chemistry cont’d
CAG
Chapter 2 | Slide 15
Measurements in Chemistry
Practice: Significant Figures
How many significant figures are in the following
numbers?
Chapter 2 | Slide 16
Measurements in Chemistry cont’d
Fig. 2.6
The digital readout on
an electronic
calculator usually
shows more digits
than are needed.
Chapter 2 | Slide 17
Measurements in Chemistry
Rounding off Numbers
• The number of significant figures in measurements affects
any calculations done with these measurements
Your calculated answer can only be as certain as the numbers used in
the calculation
Usually the calculator will show more significant digits than
are needed
If the first digit to be deleted is _____ or less, simply drop it and all the
following digits
If the first digit to be deleted is _____ or greater, that digit and all that
follow are dropped and the last retained digit is increased by _____
Chapter 2 | Slide 18
Measurements in Chemistry
Practice: Rounding Off Numbers
Round the following to 3 significant figures
28.394
0.000230600
2568
2562
Chapter 2 | Slide 19
Measurements in Chemistry
Significant Figures and Calculations
Addition/Subtraction
Results are reported to the fewest decimal place
Perform the following calculations to the correct
number of significant digits:
123.21 + 0.011 = 123.2210
3420. + 2400. + 1005 = 6825.
3420 + 2400 + 1005 = 6825
123.56 – 35.204 = 88.3560
Chapter 2 | Slide 20
Measurements in Chemistry
Significant Figures and Calculations
Multiplication/Division
Results are reported to the fewest number of significant
figures
Perform the following calculations to the correct
number of significant figures:
124.54 in x 2.2 in =
98.5564 cm2 / 45.68 cm =
504 m x 230 m =
Chapter 2 | Slide 21
Measurements in Chemistry
Mixed Functions and Significant Figures
What is the result (to the correct number of significant figures) of
the following calculations?
(23-21) x (24.4-23.1) =
(298-271) x (322) =
Chapter 2 | Slide 22
Measurements in Chemistry
Scientific Notation must be used when magnitude of
numbers are very large or very small.
Consider 1 drop of blood: 92% water by mass
There are 1,600,000,000,000,000,000,000 molecules of
water each of which has a mass of
0.000000000000000000000030 gram.
1.6 x 1021 molecules of water
3.0 x 10-23 g
__________ x ______________
Chapter 2 | Slide 23
Measurements in Chemistry
Scientific Notation
Shorthand for very large or very small numbers
In scientific notation you write a number in two parts:
The product of a number between one and ten (the coefficient)
& an appropriate power of ten.
2.5 x 105
In scientific notation, the coefficient shows only the
significant figures/digits.
Chapter 2 | Slide 24
Measurements in Chemistry
Exponents in Scientific Notation
The value of the exponent tells how many times to
multiply or divide by 10
1 x 103 = 1 x 10 x 10 x 10 = 1000
1 x 10-3 = 1  10  10  10 = 0.001
Example: 6.02 x 1023 Positive exponent means
multiply by ten (23 times)
Example: 3 x 10-4
Negative exponent means divide by ten (4 times)
Chapter 2 | Slide 25
Measurements in Chemistry
Calculations in Scientific Notation
For Multiplication: ______________ Exponents
For Division: __________________ Exponents
For Addition and Subtraction all numbers must be
expressed to the _________ exponential power.
Chapter 2 | Slide 26
Measurements in Chemistry
Calculations in Scientific Notation
The significant figures are those in the ___________
Usually, numbers in scientific notation will be
multiplied or divided
Perform the following calculations:
(9.43 x 105) / (6.02 x 1023) =
(2.367 x 10-2) x (4.5 x 105) =
Make a note of how to enter scientific notation on your
calculator:
Chapter 2 | Slide 27
Measurements in Chemistry
Additional Practice with Exponents.
(2.0 x 104) x (3.0 x 103) = 6.0 x 10
(8.8 x 107) / (2.0 x 105) = 17.6 x 10
(2.5 x 102) + (3.0 x 104)
(1.0 x 101) – (1.0 x 10-3)
Chapter 2 | Slide 28
Measurements in Chemistry
(2.5 x 102) + (3.0 x 104)
Chapter 2 | Slide 29
Measurements in Chemistry
(1.0 x 101) – (1.0 x 10-3)
Chapter 2 | Slide 30
Measurements in Chemistry
Conversion Factors
A conversion Factor is a ratio that specifies how one
unit of measurement relates to another
Creating conversion factors from equalities
12 in.= 1 ft
I L = 1000 mL
Chapter 2 | Slide 31
Measurements in Chemistry cont’d
Fig. 2.7
It is experimentally
determined that 1 inch
equals 2.54 cm, or 1
cm equals 0.394 inch
Chapter 2 | Slide 32
Measurements in Chemistry
1.00 cm = 0.394 in
1.00 in = 2.54 cm
Chapter 2 | Slide 33
Measurements in Chemistry cont’d
Table 2.2
Chapter 2 | Slide 34
Chapter 2 | Slide 35
Measurements in Chemistry cont’d
 CAG 2.1
Chapter 2 | Slide 36
Measurements in Chemistry
Dimensional Analysis
• A problem solving method in which the units
(associated with numbers) are used as a guide in
setting up the calculations.
 desired unit 
  Answer in desired units
Measuremen t in given unit x 
 given unit 
____________________
Chapter 2 | Slide 37
Measurements in Chemistry
The Steps of Dimensional Analysis
1. What is the ________? What do you want to ____ up with?
2. Write an = then write the information and unit you are _____
to start
3. Look for a _________ factor or chain of _______ that contain
both the _____ you _______ with and the units you want in
the _____
4. Multiply the ______ on the left by the conversion factor with
the units you want on the ___ and the units you start with on
the _______.
5. Make sure your units ______ out.
Chapter 2 | Slide 38
Measurements in Chemistry
Examples
Convert 180 pounds to kilograms
How many cups of water do you need for a recipe
that calls for 3 pints? (1 pint = 2 cups)
Convert 0.053 km to meters
Chapter 2 | Slide 39
Dimensional Analysis
Convert 180 pounds to kilograms
Chapter 2 | Slide 40
Dimensional Analysis
How many cups of water do you need for a recipe that calls
for 3 pints? (1 pint = 2 cups)
Chapter 2 | Slide 41
Dimensional Analysis
Convert 0.053 km to meters
Chapter 2 | Slide 42
Measurements in Chemistry
Examples
How many meters equal 3.000 ft?
Chapter 2 | Slide 43
Dimensional Analysis
How many Liters equal 350 cubic inches?
Chapter 2 | Slide 44
A pediatric dosage of a certain antibiotic is 32 mg/kg of body
weight per day. How much antibiotic, in milligrams per day,
should be administered to a child who weighs 15.9 kg?
Chapter 2 | Slide 45
Measurements in Chemistry cont’d
Fig. 2.8
Both of these items
have a mass of 23
grams, but they have
very different
volumes; therefore,
their densities are
different as well.
Chapter 2 | Slide 46
Measurements in Chemistry
What is Density?
• A ratio of the ____ of an object divided by its ______
• Typical units = ______ or ______
• We have an unknown metal with a mass of 59.24 g
and a volume of 6.64cm3 What is its density?
Chapter 2 | Slide 47
Measurements in Chemistry cont’d
Table 2.3
Chapter 2 | Slide 48
Measurements in Chemistry cont’d
Fig. 2.9
The penny is less dense
than the mercury it floats
on.
Chapter 2 | Slide 49
Measurements in Chemistry
What does density have to do with what we have been
talking about?
It’s a conversion factor!!!!!!
Examples:
What is the mass of 15 mL of Hg (mercury)? (d = 13.55 g/mL)
You have been given 150 g of ethyl alcohol, which has a density
of 0.789 g/mL. How much volume does it take up? Will it fit
into a 150 mL beaker?
Chapter 2 | Slide 50
Density
What is the mass of 15 mL of Hg (mercury)? (d = 13.55
g/mL)
Chapter 2 | Slide 51
Density
You have been given 150 g of ethyl alcohol, which has a density of 0.789
g/mL. How much volume does it take up? Will it fit into a 150 mL
beaker?
Chapter 2 | Slide 52
Measurements in Chemistry cont’d
CC 2.1
The mass of a person is
measured in both air and
when submerged in water.
These measurements are
used to calculate a person’s
density and percent body fat.
Chapter 2 | Slide 53
Measurements in Chemistry
Heat v. Temperature
Heat
A form of ____________
Always flows from objects with ______ temperature to
objects of _____ temperature
Temperature
An indicator of the tendency of _____ energy to be
transferred
A measure of how ____ or _____ an object is
Chapter 2 | Slide 54
Measurements in Chemistry cont’d
Fig 2.10
The relationships
among the Celsius,
Kelvin, and Fahrenheit
temperature scales are
determined by the
degree sizes and the
reference point values.
Chapter 2 | Slide 55
Measurements in Chemistry
Converting Between Temperature Scales
Conversions between Celsius and Kelvin
(temperature in K) = (temperature in oC) + 273
(temperature in oC) = (temperature in K) – 273
Conversions between Celsius and Fahrenheit
oF
= 9/5 (oC) + 32
oC = 5/9(oF – 32)
Chapter 2 | Slide 56
Measurements in Chemistry
Heat Energy
Form of energy most often _________ or _________ by
chemical reactions and physical changes
The calorie (cal) is a common ____ of energy, and is the
amount of heat energy needed to raise the temperature
of _______ of water by 1 _______ _________.
1 kilocalorie = _____ calories
The joule (J) is another unit for heat energy (q)
1 calorie = 4.184 joules
Chapter 2 | Slide 57
Measurements in Chemistry
Specific heat (c):
Quantity of heat energy needed to raise the temperature
of _______ of a substance by __________ Celsius
Units: J/goC or cal/goC
The higher the specific heat of a substance, the _____ its
temperature will ________ when heat is added to it
Chapter 2 | Slide 58
Measurements in Chemistry cont’d
Table 2.4
Specific Heats of
common substances
Chapter 2 | Slide 59
Measurements in Chemistry
The Effect of the High Specific Heat of Water
Chapter 2 | Slide 60
A horse trainer exercises a horse twice each day, every day, seven days each week. The
horse is run 5 laps each morning and 5 laps each afternoon. The length of the race track
is 0.875 miles. Most horse races are measured in furlongs with exactly 8 furlongs
equaling exactly one mile. How many furlongs does the horse run over a period of a
fortnight (2 weeks)? Show all of your work for full credit.
Hint:
? furlongs = 1 fortnight
61
A dump truck is designed to hold 5.50 cubic yds (yd3). What is this volume in
cubic centimeters (cc or cm3)? Hint: 1 cubic yd measures exactly 3 ft or 36
inches on each side. Express you answer in proper scientific notation. (5
points) Show all of your work for full credit.
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