Transcript - Dr. Parvin Carter Dr. Parvin Carter

Fundamentals of General, Organic &
Biological Chemistry
Chapter Two
Measurements in
Chemistry
Stating a Measurement
 In every measurement, a number is followed
by a unit.
 Observe the following examples of
measurements:
number + unit
35 m
0.25 L
225 lb
3.4 hr
2
The Metric System (SI)
The metric system is
 A decimal system
based on 10.
 Used in most of the
world.
 Used by scientists
and in hospitals.
3
Units in the Metric System
In the metric and SI systems, a basic unit
identifies each type of measurement:
4
Length Measurement
 In the metric system, length is measured in
meters using a meter stick.
 The metric unit for length is the meter (m).
5
Volume Measurement




Volume is the space
occupied by a substance.
The metric unit of
volume is the liter (L).
The liter is slightly bigger
than a quart.
A graduated cylinder is
used to measure the
volume of a liquid.
6
Mass Measurement



The mass of an object
is the quantity of
material it contains.
A balance is used to
measure mass.
The metric unit for
mass is the gram (g).
7
Learning Check
In each of the following, indicate whether the
unit describes 1) length 2) mass or 3) volume.
____ A. A bag of tomatoes is 4.6 kg.
____ B.
A person is 2.0 m tall.
____ C.
A medication contains 0.50 g Aspirin.
____ D.
A bottle contains 1.5 L of water.
8
Solution
In each of the following, indicate whether the unit
describes 1) length 2) mass or 3) volume.
2 mass A. A bag of tomatoes is 4.6 kg.
1 length B.
A person is 2.0 m tall.
2 mass
A medication contains 0.50 g Aspirin.
C.
3 volume D.
A bottle contains 1.5 L of water.
9
Learning Check
Identify the measurement that has a metric unit.
A. John’s height is
1) 1.5 yards
2) 6 feet
3) 2 meters
B. The volume of saline in the IV container is
1) 1 liter
2) 1 quart
3) 2 pints
C. The mass of a lemon is
1) 12 ounces 2) 145 grams
3) 0.6 pounds
10
Solution
A. John’s height is
3) 2 meters
B. The volume of saline in the IV container is
1) 1 liter
C. The mass of a lemon is
2) 145 grams
11
Scientific Notation

A number in scientific notation contains a
coefficient and a power of 10.
coefficient power of ten

coefficient power of ten
1.5 x 102
7.35 x 10-4
Place the decimal point after the first digit.
Indicate the spaces moved as a power of ten.
52 000 = 5.2 x 104
10-3
0.00378 = 3.78 x
4 spaces left
3 spaces right
12
Learning Check
Select the correct scientific notation for each.
A. 0.000 008
1) 8 x 106
2) 8 x 10-6 3) 0.8 x 10-5
B. 72 000
1) 7.2 x 104
2) 72 x 103 3) 7.2 x 10-4
13
Solution
Select the correct scientific notation for each.
A. 0.000 008
2) 8 x 10-6
B. 72 000
1) 7.2 x 104
14
Learning Check
Write each as a standard number.
A. 2.0 x 10-2
1) 200
2) 0.02
3) 0.020
B. 1.8 x 105
1) 180 000
2) 0.000018
3) 18 000
15
Solution
Write each as a standard number.
A. 2.0 x 10-2
3) 0.020
B. 1.8 x 105
1) 180 000
16
Measured Numbers


You use a
measuring tool to
determine a
quantity such as
your height or the
mass of an object.
The numbers you
obtain are called
measured numbers.
17
Reading a Meter Stick
. l2. . . . l . . . . l3 . . . . l . . . . l4. .


cm
To measure the length of the blue line, we
read the markings on the meter stick.
The first digit
2
plus the second digit
2.7
Estimating the third digit between 2.7–2.8
gives a final length reported as
2.75 cm
or
2.76 cm
18
Accuracy – how close a measurement is to the true value
Precision – how close a set of measurements are to each other
accurate
&
precise
precise
but
not accurate
Chapter 01
not accurate
&
not precise
Slide 19
Mass of a Tennis Ball
good accuracy
good precision
20
Mass of a Tennis Ball
good accuracy
poor precision
21
Mass of a Tennis Ball
poor accuracy
poor precision
22
Known + Estimated Digits
 In the length measurement of 2.76 cm,
 the digits 2 and 7 are certain (known).
 the third digit 5(or 6) is estimated (uncertain).
 all three digits (2.76) are significant including
the estimated digit.
23
Learning Check
. l8. . . . l . . . . l9. . . . l . . . . l10. . cm
What is the length of the red line?
1) 9.0 cm
2) 9.03 cm
3) 9.04 cm
24
Solution
. l8. . . . l . . . . l9. . . . l . . . . l10. . cm
The length of the red line could be reported as
2) 9.03 cm
or
3) 9.04 cm
The estimated digit may be slightly different.
Both readings are acceptable.
25
Zero as a Measured Number
. l3. . . . l . . . . l4. . . . l . . . . l5. . cm




The first and second digits are 4.5.
In this example, the line ends on a mark.
Then the estimated digit for the hundredths
place is 0.
We would report this measurement as 4.50 cm.
26
Exact Numbers
 An exact number is obtained when you count
objects or use a defined relationship.
Counting objects
2 soccer balls
4 pizzas
Defined relationships
1 foot = 12 inches
1 meter = 100 cm
 An exact number is not obtained with a
measuring tool.
27
Learning Check
A. Exact numbers are obtained by
1. using a measuring tool
2. counting
3. definition
B. Measured numbers are obtained by
1. using a measuring tool
2. counting
3. definition
28
Solution
A. Exact numbers are obtained by
2. counting
3. definition
B. Measured numbers are obtained by
1. using a measuring tool
29
Learning Check
Classify each of the following as an exact (1) or a
measured (2) number.
A.__Gold melts at 1064°C.
B.__1 yard = 3 feet
C.__The diameter of a red blood cell is 6 x 10-4 cm.
D.__There are 6 hats on the shelf.
E.__A can of soda contains 355 mL of soda.
30
Solution
Classify each of the following as an exact (1) or a
measured(2) number.
A. 2 A measuring tool is required.
B. 1 This is a defined relationship.
C. 2 A measuring tool is used to determine
length.
D. 1 The number of hats is obtained by counting.
E. 2 The volume of soda is measured.
31
2.4 Measurement and Significant Figures
Every
experimental
measurement,
no
matter how precise,
has a degree of
uncertainty to it
because there is a
limit to the number
of digits that can be
determined.

32
Accuracy, Precision, and
Significant Figures
0 cm
1
2
3
4
1.7 cm < length < 1.8 cm
length = 1.74 cm
Slide 33
Chapter 01





Rules for determining significant figures
1.Zeroes in the middle of a number are
significant. 69.08 g has four significant
figures, 6, 9, 0, and 8.
2.Zeroes at the beginning of a number are not
significant. 0.0089 g has two significant
figure, 8 and 9.
3.Zeroes at the end of a number and after the
decimal points are significant. 2.50 g has three
significant figures 2, 5, and 0.
25.00 m has four significant figures 2, 5, 0,
and 0.
34

4. Zeroes at the end of a number and before
an implied decimal points may or may not be
significant. 1500 kg may have two, three, or
four significant figures. Zeroes here may be
part of the measurements or for simply to
locate the unwritten decimal point.
35
Which of the following measurements
has three significant figures?
a.
b.
c.
d.
e.
1,207 g
4.250 g
0.006 g
0.0250 g
0.03750 g
36
Which of the following measurements
has three significant figures?
a.
b.
c.
d.
e.
1,207 g
4.250 g
0.006 g
0.0250 g
0.03750 g
37
Which of the following numbers
contains four significant figures?
a.
b.
c.
d.
e.
230,110
23,011.0
0.23010
0.0230100
0.002301
38
Which of the following numbers
contains four significant figures?
a.
b.
c.
d.
e.
230,110
23,011.0
0.23010
0.0230100
0.002301
39
2.6 Rounding off Numbers
Often calculator produces large number as
a result of a calculation although the number
of significant figures is good only to a
fewer number than the calculator has
produced – in this case the large number
may be rounded off to a smaller number
keeping only significant figures.

40

Rules for Rounding off Numbers:
Rule 1 (For multiplication and divisions): The
answer can’t have more significant figures than either
of the original numbers.

41
Rule 2 (For addition and subtraction):
The answer should have minimum decimal
places.

42
How many significant figures
should be shown for the
calculation?





1
2
3
4
5
1.25 0.45
2.734

43
How many significant figures
should be shown for the
calculation?





1
2
3
4
5
1.25 0.45
2.734

44
How many significant figures are there
in the following number: 1.200 X 109?
2. 3
3. 2
4. 1
5. Cannot deduce from
given information.
45
Correct Answer:
1. 4
2. 3
3. 2
4. 1
5. Cannot deduce from
given information.
1.200  109
Zeros that fall both at
the end of a number and
after the decimal point
are always significant.
46
How many significant figures are there
in the following summation:
1.
2.
3.
4.
5.
2
3
4
5
6
6.220
1.0
+ 125
47
Correct Answer:
1.
2.
3.
4.
5.
2
3
4
5
6
6.220
1.0
+ 125
132.220
In addition and subtraction the result can have
no more decimal places than the measurement
with the fewest number of decimal places.
48
How many significant figures are there
in the result of the following
multiplication:
(2.54)  (6.2)  (12.000)
1.
2.
3.
4.
2
3
4
5
49
Correct Answer:
1.
2.
3.
4.
2
3
4
5
(2.54)  (6.2)  (12.000) = 188.976 = 190
In multiplication and division the result must be
reported with the same number of significant
figures as the measurement with the fewest
significant figures.
50
2.7 Problem Solving: Converting a
Quantity from One Unit to Another
Factor-Label-Method (Unit Conversion Factor):

A quantity in one unit is converted to an
equivalent quantity in a different unit by using
a conversion factor that expresses the
relationship between units.

51
52
When solving a problem, set up an equation so that
all unwanted units cancel, leaving only the desired
unit. For example, we want to find out how many
kilometers are there in 26.22 mile distance. We will
get the correct answer if we multiply 26.22 mi by the
conversion factor km/mi.

53
Problem Setup



In working a problem, start with the initial
unit.
Write a unit plan that converts the initial
unit to the final unit.
Unit 1
Unit 2
Select conversion factors that cancel the
initial unit and give the final unit.
Initial x
Conversion =
Final
unit
factor
unit
Unit 1 x
Unit 2
=
Unit 2
Unit 1
54
Setting up a Problem
How many minutes are 2.5 hours?
Solution:
Initial unit
=
2.5 hr
Final unit
=
? min
Unit Plan
=
hr
min
Setup problem to cancel hours (hr).
Inital
Conversion
Final
unit
factor
unit
2.5 hr x 60 min
= 150 min (2 SF)
1 hr
55
Learning Check
A rattlesnake is 2.44 m long. How long is
the snake in cm?
1) 2440 cm
2) 244 cm
3) 24.4 cm
56
Solution
A rattlesnake is 2.44 m long. How long is
the snake in centimeters?
2) 244 cm
2.44 m x 100 cm
1m
= 244 cm
57
Using Two or More Factors
 Often, two or more conversion factors are
required to obtain the unit of the answer.
Unit 1
Unit 2
Unit 3
 Additional conversion factors are placed in
the setup to cancel the preceding unit
Initial unit x factor 1 x factor 2 = Final unit
Unit 1
x Unit 2 x Unit 3 = Unit 3
Unit 1
Unit 2
58
Example: Problem Solving
How many minutes are in 1.4 days?
Initial unit: 1.4 days
Unit plan: days
hr
min
Set up problem:
1.4 days x 24 hr x 60 min = 2.0 x 103 min
1 day
1 hr
2 SF
Exact
Exact = 2 SF
59
Check the Unit Cancellation
 Be sure to check your unit cancellation in the
setup.
 What is wrong with the following setup?
1.4 day x 1 day x 1 hr
24 hr
60 min
Units = day2/min is Not the final unit needed
Units don’t cancel properly.

The units in the conversion factors must cancel to
give the correct unit for the answer.
60
Learning Check
An adult human has 4650 mL of blood.
How many gallons of blood is that?
Unit plan: mL
qt
gallon
Equalities: 1 quart = 946 mL
1 gallon = 4 quarts
61
Solution
Unit plan:
Setup:
4650 mL x
3 SF
mL
qt
1 qt
x
946 mL
exact
gallon
1 gal
= 1.23 gal
4 qt
exact
3 SF
62
Typical Steps in Problem Solving







Identify the initial and final units.
Write out a unit plan.
Select appropriate conversion factors.
Convert the initial unit to the final unit.
Cancel the units and check the final unit.
Do the math on a calculator.
Give an answer using significant figures.
63
Learning Check
If a ski pole is 3.0 feet in length, how long
is the ski pole in mm?
64
Solution
3.0 ft x 12 in x 2.54 cm x 10 mm =
1 ft
1 in.
1 cm
Check factor setup:
Units cancel properly
Check final unit:
mm
Calculator answer:
914.4 mm
Final answer:
910 mm (2 SF rounded)
65
Learning Check
If your pace on a treadmill is 65 meters per
minute, how many minutes will it take for you to
walk a distance of 7500 feet?
66
Solution
7500 ft x
x 1 min
65 m
12 in. x 2.54 cm
1 ft
1 in.
x 1m
100 cm
= 35 min
final answer (2 SF)
67
Clinical Factors


Conversion factors are also possible when working
with medications.
A drug dosage such as 20 mg Prednisone per
tablet can be written as
20 mg Prednisone and
1 tablet
1 tablet
20 mg Prednisone
68
Learning Check
The dosage ordered is 400 mg of Erythromycin
four times a day (q.i.d)*. If the oral suspension
contains 200 mg Erythromycin/5 mL, how
many mL will be given each time?
1) 5 mL
2) 10 mL
3) 40 mL
*:Latin quater in die
69
Solution
The dosage ordered is 400 mg of Erythromycin
four times a day (q.i.d). If the oral suspension
contains 200 mg Erythromycin/5 mL, how
many mL will be given each time?
2) 10 mL
400 mg x 5 mL
= 10 mL
200 mg
70
Temperature Scales
 Temperature is
measured using the
Fahrenheit,
Celsius, and Kelvin
temperature scales.
 The reference
points are the
boiling and
freezing points of
water.
71
Learning Check
A. What is the temperature of freezing water?
1) 0°F
2) 0°C
3) 0 K
B. What is the temperature of boiling water?
1) 100°F
2) 32°F
3) 373 K
C. How many Celsius units are between the
boiling and freezing points of water?
1) 100
2) 180
3) 273
72
Solution
A. What is the temperature of freezing water?
2) 0°C
B. What is the temperature of boiling water?
3) 373 K
C. How many Celsius units are between the
boiling and freezing points of water?
1) 100
73
Fahrenheit Formula


On the Fahrenheit scale, there are are 180°F
between the freezing and boiling points and on
the Celsius scale, there are 100 °C.
180°F = 9°F = 1.8°F
100°C
5°C
1°C
In the formula for Fahrenheit, the value of 32
adjusts the zero point of water from 0°C to 32°F.
°F = 9/5 T°C + 32
or °F = 1.8 T°C + 32
74
Celsius Formula


The equation for Fahrenheit is rearranged to
calculate T°C.
°F
= 1.8 T°C + 32
Subtract 32 from both sides and divide by 1.8.
°F – 32
°F – 32
1.8
°F – 32
1.8
=
=
=
1.8T°C ( +32 – 32)
1.8 T°C
1.8
T°C
75
Solving A Temperature Problem
A person with hypothermia
has a body temperature of
34.8°C. What is that
temperature in °F?
°F = 1.8 (34.8°C) + 32
exact tenth's
=
=
exact
62.6 + 32
94.6°F
tenth’s
76
Learning Check
The normal temperature of a chickadee is
105.8°F. What is that temperature in °C?
1) 73.8 °C
2) 58.8 °C
3) 41.0 °C
77
Solution
3) 41.0 °C
°C =
=
=
(°F – 32)
1.8
(105.8 – 32)
1.8
73.8°F
1.8°
=
41.0°C
78
Learning Check
A pepperoni pizza is baked at 455°F. What
temperature is needed on the Celsius scale?
1) 437 °C
2) 235°C
3) 221°C
79
Solution
A pepperoni pizza is baked at 455°F. What
temperature is needed on the Celsius scale?
2) 235°C
(455 – 32) = 235°C
1.8
80
Learning Check
On a cold winter day, the temperature is –15°C.
What is that temperature in °F?
1) 19°F
2) 59°F
3) 5°F
81
Solution
3) 5°F
°F = 1.8(–15°C) + 32
= – 27 + 32
= 5°F
Note: Be sure to use the change sign key on
your calculator to enter the minus – sign.
1.8 x 15 +/ – = –27
82
2.10 Energy and Heat
Energy: Capacity to do work or supply energy.
Classification of Energy:
1.
Potential Energy: stored energy.

Example: a coiled spring have potential
energy waiting to be released.
2.
Kinetic Energy: energy of motion.
Example, when the spring uncoil potential
energy is converted to the kinetic energy.


83
Learning Check
Identify the energy as 1) potential or 2) kinetic
A. Roller blading.
B. A peanut butter and jelly sandwich.
C. Mowing the lawn.
D. Gasoline in the gas tank.
84
Solution
Identify the energy as 1) potential or 2) kinetic
A. Roller blading. (2 kinetic)
B. A peanut butter and jelly sandwich. (1 potential)
C. Mowing the lawn. (2 kinetic)
D. Gasoline in the gas tank. (1 potential)
85
Forms of Energy
Energy has many forms:
 Mechanical
 Electrical
 Thermal (heat)
 Chemical
 Solar (light)
 Nuclear
86
Heat
 Heat energy flows from a warmer object to
a colder object.
 The colder object gains energy when it is
heated.
 During heat flow, the loss of heat by a
warmer object is equal to the heat gained
by the colder object.
87
Some Equalities for Heat
 Heat is measured in calories or joules.
1 kilocalorie (kcal) = 1000 calories (cal)
1 calorie = 4.18 Joules (J)
1 kJ = 1000 J
88
Specific Heat
Specific heat is the
amount of heat
(calories or Joules)
that raises the
temperature of 1 g
of a substance by
1°C.
89
Learning Check
A. A substance with a large specific heat
1) heats up quickly
2) heats up slowly
B. When ocean water cools, the surrounding air
1) cools
2) warms
3) stays the same
C. Sand in the desert is hot in the day and cool
at night. Sand must have a
1) high specific heat
2) low specific heat
90
Solution
A. A substance with a large specific heat
2) heats up slowly
B. When ocean water cools, the surrounding air
2) warms
C. Sand in the desert is hot in the day and cool
at night. Sand must have a
2) low specific heat
91
Learning Check
When 200 g of water are heated, the water
temperature rises from 10°C to 18°C.
200 g
400 g
If 400 g of water at 10°C are heated with the
same amount of heat, the final temperature
would be
1) 10 °C
2) 14°C
3) 18°C
92
Solution
When 200 g of water are heated, the water
temperature rises from 10°C to 18°C.
200 g
400 g
If 400 g of water at 10°C are heated with the
same amount of heat, the final temperature
would be
2) 14°C
93
Calculation with Specific Heat
 To calculate the amount of heat lost or gained by a
substance, we need the Specific Heat of substance,
T, and the mass of the substance.
 Heat = g x T x cal (or J) = cal ( or J)
g °C
94
Sample Calculation for Heat
A hot-water bottle contains 750 g of water at
65°C. If the water cools to body temperature
(37°C), how many calories of heat could be
transferred to sore muscles?
The temperature change is 65°C - 37°C = 28°C.
heat (cal) =
g x T x Sp. Ht. (H2O)
750 g x 28°C x 1.00 cal
g°C
= 21 000 cal
95
Learning Check
How many kcal are needed to raise the
temperature of 120 g of water from 15.0°C to
75.0°C?
1) 1.8 kcal
2) 7.2 kcal
3) 9.0 kcal
96
Learning Check
How many kcal are needed to raise the
temperature of 120 g of water from 15.0°C to
75.0°C?
2) 7.2 kcal
97



In chemical reactions, the potential energy
is often converted into heat. Reaction
products have less potential energy than the
reactants – the products are more stable
than the reactants.
Stable products have very little potential
energy remaining as a result have very little
tendency to undergo further reaction.
SI unit of energy is Joules (J) and the
metric unit of energy is calorie (cal).
98
2.11 Density
Density relates the mass of an object with its
volume. Density is usually expressed in units as Gram per cubic centimeter (g/cm3) for solids, and
Gram per milliliter (g/mL) for liquids.

Density =
Mass (g)
Volume (mL or cm3)
99
Learning Check
Osmium is a very dense metal. What is its
density in g/cm3 if 50.00 g of the metal
occupies a volume of 2.22 cm3?
1) 2.25 g/cm3
2) 22.5 g/cm3
3) 111 g/cm3
100
Solution
Place the mass of the osmium metal in the
numerator of the density setup and its volume
in the denominator.
D
=
mass
volume
calculator
final answer
=
=
=
50.00 g
2.22 cm3
22.522522 g/cm3
22.5 g/cm3
101
Density Using Volume
Displacement
 The volume of zinc is calculated from the displaced
volume
45.0 mL - 35.5 mL = 9.5 mL = 9.5 cm3
 Density zinc = mass = 68.60 g = 7.2 g/cm3
volume
9.5 cm3
102
Learning Check
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
2) 6 g/cm3 3) 252 g/cm3
25 mL
33 mL
object
103
Solution
2) 6 g/cm3
Calculate the volume difference.
33 mL – 25 mL = 8 mL
Convert the volume in mL to cm3.
8 mL x 1 cm3 = 8 cm3
1 mL
Set up the density calculation
Density = mass
= 48 g
volume
8 cm3
=
6 g = 6 g/cm3
cm3
104
Sink or Float
Ice floats in water because the density of ice is less
than the density of water. Aluminum sinks because
it has a density greater than the density of water.
105
Learning Check
Which diagram correctly represents the liquid
layers in the cylinder? Karo (K) syrup (1.4 g/mL),
vegetable (V) oil (0.91 g/mL,) water (W) (1.0 g/mL)
V
W
K
W
K
V
K
V
W
1
2
3
106
Solution
1)
V vegetable oil 0.91 g/mL
W water 1.0 g/mL
K Karo syrup 1.4 g/mL
107
Density as a Conversion Factor

Density represents an equality for a substance.
The mass in grams is for 1 mL. For a substance
with a density of 3.8 g/mL, the equality is:
3.8 g = 1 mL

For this equality, we can write two conversion
factors.
Conversion
factors
3.8 g
1 mL
and
1 mL
3.8 g
108
Learning Check
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
109
Solution
1) 0.614 kg
Unit plan: mL  g  kg
Equalities: density
and
1 mL = 0.702 g
1 kg = 1000 g
Setup: 875 mL x 0.702 g x 1 kg = 0.614 kg
1 mL
1000 g
density
factor
metric
factor
110
Learning Check
If blood has a density of 1.05 g/mL, how
many liters of blood are donated if 575 g of
blood are given?
1) 0.548 L
2) 1.25 L
3) 1.83 L
111
Solution
1)
0.548 L
Unit Plan: g
mL
575 g
x
x
1 mL
1.05 g
density
factor
L
1L
1000 mL
=
0.548 L
metric
factor
112
Density Using Volume
Displacement
 The volume of zinc is calculated from the displaced
volume
45.0 mL - 35.5 mL = 9.5 mL = 9.5 cm3
 Density zinc = mass = 68.60 g = 7.2 g/cm3
volume
9.5 cm3
113
Learning Check
A group of students collected 125 empty
aluminum cans to take to the recycling
center. If 21 cans make 1.0 pound of
aluminum, how many liters of aluminum
(D=2.70 g/cm3) are obtained from the cans?
1) 1.0 L
2) 2.0 L
3) 4.0 L
114
Solution
1) 1.0 L
125 cans x
1.0 lb x 454 g
21 cans
1 lb
x 1 mL x
1L
1 cm3
1000 mL
x
1 cm3
2.70 g
= 1.0 L
115
Learning Check
You have 3 metal samples. Which one will
displace the greatest volume of water?
1
2
3
25 g of aluminum
2.70 g/mL
45 g of gold
19.3 g/mL
75 g of lead
11.3 g/mL
116
Solution
1)
25 g of aluminum
2.70 g/mL
Calculate the volume for each metal and
select the metal that has the greatest volume.
1) 25 g x 1 mL
= 9.3 mL aluminum
2.70 g
2) 45 g x 1 mL
= 2.3 mL gold
19.3 g
3) 75 g x 1 mL
= 6.6 mL lead
11.3 g
117
2. 12 Specific Gravity
Specific Gravity (sp gr): density of a substance
divided by the density of water at the same
temperature. Specific Gravity is unitless. At
normal temperature, the density of water is close
to 1 g/mL. Thus, specific gravity of a substance
at normal temperature is equal to the density.

Density of substance (g/ml)
Specific gravity =
Density of water at the same temperature (g/ml)
118
The specific gravity of a
liquid can be measured using
an instrument called a
hydrometer, which consists of
a weighted bulb on the end of
a calibrated glass tube, as
shown in the following Fig
2.6. The depth to which the
hydrometer sinks when placed
in a fluid indicates the fluid’s
specific gravity.

119
Learning Check
Corn oil has a density of 0.92 g/mL. What is
the specific gravity of corn oil?
1) 0.92
2) 0.92 g
3) 1.1
120
Solution
Corn oil has a density of 0.92 g/mL.
What is the specific gravity of corn oil?
1) 0.92
specific gravity = 0.92 g/mL = 0.92
1.00 g/mL
121
Learning Check
A bone sample has a mass of 52 g. If bone has
a specific gravity of 1.8, what is the volume in
milliliters of the bone sample?
1) 1.8 mL
2) 29 mL
3) 94 mL
122
Solution
2) 29 mL
Convert the specific gravity to its density
using the density of water
1.8 x 1.00 g/mL = 1.8 g/mL
Use the density factor to cancel the initial unit.
Volume = 52 g x 1 mL = 29 mL
1.8 g
123
Chapter Summary




Physical quantity, a measurable properties, is
described by both a number and a unit.
Mass, an amount of matter an object contains,
is measured in kilograms (kg) or grams (g).
Volume is measured in cubic meters (m3) or in
liter (L) or milliliters (mL).
Temperature is measured in Kelvin (K) in SI
system and in degrees Celsius (oC) in the metric
system.
124
Chapter Summary Contd.





Measurement of small or large numbers are
usually written in scientific notation, a product of
a number between 1 and 10 and a power of 10.
A measurement in one unit can be converted to
another unit by multiplying by a conversion
factor.
Energy: the capacity to supply heat or to do
work.
Potential energy – stored energy.
kinetic energy – energy of moving particles.
125
Chapter Summary Contd.





Heat: kinetic energy of moving particles in a
chemical reaction.
Temperature: is a measure of how hot or cold an
object is.
Specific heat: amount of heat necessary to raise
the temperature of 1 g of the substance by 1oC.
Density: grams per milliliters for a liquid or
gram per cubic centimeter for a solid.
Specific gravity: density of a liquid divided by
the density of water.
126

End of Chapter 2
127