Standards for Measurement. Preparation for College Chemistry Columbia University Department of Chemistry. The Scientific Method. http://antoine.fsu.umd.edu/chem/senese/101/intro/scimethodquiz.shtml. Observations. Laws. (analysis). Hypothesis. (explanation). Experiment. (measurement).
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Preparation for College Chemistry
Columbia University
Department of Chemistry
http://antoine.fsu.umd.edu/chem/senese/101/intro/scimethodquiz.shtml
Observations
Laws
(analysis)
Hypothesis
(explanation)
Experiment
(measurement)
(analysis)
Theory
(Model)
2
3
4
5
6
7
8
Measurement and Interpretations
Direct Measurement
Interpretation Step
Diameter = 2.5 cm
Radius = Diameter/2
Area = x r2 = 8.04 cm2
Art of Chemical Measurement:
ms
y
x
Na+
K+
Na+
Na+
K+
Na+
K+
+
+
+
+
+
+






Na+
K+
Na+
Na+
K+
Na+
K+






Na+
K+
Na+
Na+
K+
Na+
K+
+
+
+
+
+
+
Na+
K+
Na+
Na+
K+
Na+
K+
Resting Potential (Squid Experiment)
40
65
Measured Data
Basic
UNIT
Derived
Resting Potential = 65 mV
Affected by Uncertainty
NUMERICAL VALUE
This quantity contains 3 significant figures, i.e., three experimentally meaningful digits.
If the same measurement is made with an analytical balance (precision + 0.0001g) , the mass might be 23.5820 g (6 sig. fig.)
Significant Figures (Sig. Figs.)Zero is SIGNIFICANT when:
Is between nonzero digits: 61.09 has four sig Figs.
Appears at the end of a number that includes a decimal point 0.500 has three sig. Figs.; 1000. has four sig. Figs.
Zero is NON SIGNIFICANT when:
Appears before the first nonzero digit. 0.0025 has two sig. Figs. Leading Zeros are non significant
Appears at the end of a number without a decimal point. 1,000 has one sig. Fig.; 590 has two sig. Figs.
Defined numbers, like 12 inches in a foot, 60 minutes in an hour, 1,000mL in one liter.
Numbers that occur in counting operations.
Exact numbers have an infinite number of sig. figs.
Exact numbers do not limit the number of sig. figs. in a calculation.
Number written as a factor between 1 and 10 multiplied by 10 raised to a power.
Useful to unequivocally designate the significant figures.
The answer must contain as many significant figures as in the least precise quantity (measurement with least precision).
What is the density of a piece of metal weighing 36.123 g with a volume of 13.4 mL?
Drop these three digits
Round off to 7
ANSWER:
Keep only as many digits after the decimal point as there are in the least precise quantity
Ex. Add 1.223 g of sugar to 154.5 g of coffee:
Total mass = 1.2 g + 154.5 g = 155.7 g
Note that the rule for addition and subtraction does not relate to significant figures.
The number of significant figures often decreases upon subtraction.
Mass beaker + sample = 52.169 g (5 sig. figs.)
 Mass empty beaker = 52.120 g (5 sig. figs.)
Mass sample = 0.049 g (2 sig figs)
Length meter m
Mass kilogram kg
Time second s
Electric current ampere A
Temperature kelvin K
Amount of substance mole mol
Luminous intensity candela cd
Système International (SI) The Metric SystemBased on seven DIMENSIONALLY INDEPENDENT quantities
Base unit is the meter (m)
1790s: 10millionth of the distance from the equator to the North Pole along a meridian.
1889: Distance between two engraved lines on a PlatinumIridium alloy bar maintained at 0°C in SevresFrance.
19601983: 1,650,763.73 wavelengths of the orangered emision of 18Kr at standard conditions
Since 1983: 1/299,792,458 of the distance traveled by light in 1 second through vacuum.
Engineering dimensions
1 km = 103 m 1 in. = 2.54cm
1 cm = 102 m 1 mile = 1.61km
1 mm = 103 m
1 µm = 106 m
Atomic dimensions
1 nm = 109 m
1 Å = 1010 m
A mass of 1 kg has a terrestrial weight of 9.8 newtons (2.2 lbs)
Depending on the precision required and the amount of material, different balances are used:
The Quadruple Beam Balance (+ 10 mg)
The Top Loading Balance (+ 1 mg).
The Analytical Balance (+ 0.1 mg).
MassBase unit is the kilogram (kg)International prototype: a platinumIridium cylinder maintained in SevresFrance.
Kelvin
Celsius
212
373.15
100
180
100
100
32
273.15
0
Comparison of Temperature Scales
K = °C + 273.15
°C= (°F  32) / 1.8
°F= (1.8 x °C) + 32
Boiling point of water
Freezing point of water
°F= (1.8 x °C) + 32
°C= (°F  32) / 1.8
Ex. 2.20 Convert 110°F to °C and K
°C= (68° – 32°) / 1.8 = 20°C
K = 20 + 273 = 293 K
Temperature ConversionPhysical quantity Name Symbol Definition
Frequency Hertz Hz s1
Force newton N m.kg.s2
Pressure, stress pascal Pa N.m2 = m1.kg.s2
Energy work, heat joule J N.m = m2.kg.s2
Electric charge coulomb C A.s
Electromotive Force volt V J.C1 = m2.kg.s3.A1
Electric Resistance ohm V.A1 = m2.kg.s3.A2
Derived UnitsTwo conversion factors
760 mm Hg
101.3 kPa
Simple, One Step ConversionsConversion factor : 101.3 kPa = 760 mm Hg
Unit needed
pressure (mmHg) = 99.6kPa
x
= 747mmHg
Unit given
Unit given
1 in
Simple, One Step ConversionsA rainbow trout is measured to be 16.2 in. long. What is the length in cm?
x
= 41.1 cm
length in cm = 16.2 in
Note the cancellation of units. To convert from centimeters to inches, the conversion factor would be 1 in / 2.54 cm.
3600 s
miles
hour
1.609 x 10–3m
1 mile
Multiple Conversion FactorsA baseball is thrown at 89.6 miles per hour. What is the speed in meters per second?
m/s
Mile/hour
m/hour
1 mile = 1.609 km = 1.609 x 103 m; 1 h = 3600 s
x
speed = 89.6
= 40.0 m / s
x
Three sig. figs.
Intensive vs. Extensive: density vs. mass
Chemical vs. Physical
Density and Solubility
Properties of SubstancesIndependent of the amount of material
Density (mass per unit volume)
Temperature (average energy per particle)
Chemical vs. Physical Properties
Chemical Properties
Molecules or ions undergo a change in structure or composition
Physical Properties
Can be studied without a change in structure or composition
3.460g
5.00 mL
22.138
3.460g
= 0.692g / mL
d =
1 mL
0.692g
V = 10.00g x
= 14.5 mL
Density: Conversion factor mass volumeAn empty flask weighs 22.138 g. You pipet 5.00 mL of octane into the flask. The total mass is 25.598 g. What is the density?
Octane amount in g:
What is the volume occupied by ten grams of octane?
Expressed as grams of solute per 100 g of solvent in the CRC (Chemical Rubber Company) Chemistry and Physics Handbook.
For lead nitrate in aqueous solution:
140g lead nitrate
SolubilityHow much water is required to dissolve 80 g of lead nitrate at 100°C?
Mass water = 80g lead nitrate
x
= 57g water
Conversion factor
(from table)
100g water
Cool the solution to 10°C. How much lead nitrate remains in solution?
x
= 28g lead nitrate
Mass of lead nitrate = 57g water
28g lead nitrate remain in solution
80g lead nitrate were initially in solution
80g – 28g = 52g lead nitrate crystallizes out of solution
Matter
Mixtures
Pure Substances
Compounds
Homogeneous
One Phase
(Solutions)
Elements
Heterogeneous
More than one phase
1
He
2
Li
3
Be
4
5
B
C
6
7
N
8
O
F
9
Ne
10
Na
11
12
Mg
13
Al
Si
14
P
15
S
16
Cl
17
Ar
18
K
19
20
Ca
21
Sc
Ti
22
V
23
Cr
24
25
Mn
Fe
26
Co
27
Ni
28
Cu
29
Zn
30
31
Ga
32
Ge
33
As
Se
34
Br
35
36
Kr
Rb
37
Sr
38
39
Y
40
Zr
Nb
41
42
Mo
Tc
43
44
Ru
Rh
45
46
Pd
Ag
47
Cd
48
49
In
50
Sn
51
Sb
52
Te
53
I
Xe
54
Cs
55
Ba
56
57
La
Hf
72
Ta
73
W
74
75
Re
76
Os
77
Ir
78
Pt
Au
79
80
Hg
8l
Tl
Pb
82
83
Bi
Po
84
85
At
Rn
86
Fr
87
88
Ra
Ac
89
104
Rf
Ha
105
Sg
106
107
Bh
Hs
108
Mt
109
Ce
58
Pr
59
Nd
60
Pm
61
62
Sm
63
Eu
64
Gd
Tb
65
Lu
71
70
Dy
Yb
Tmi
Ho
67
69
66
68
Er
Th
90
91
Pa
92
U
Np
93
94
Pu
Am
95
96
Cm
Bk
97
102
103
Cf
Es
Fm
Md
101
99
100
Lr
98
No
, Nonmetals,
Metals
Metalloids
MainGroup Elements
MainGroup Elements
Transition Metals
InnerTransition Metals
Lantanides
Actinides
Compounds
Ionic
(Coulombic forces)
Molecular
(Covalent bonds)
Molecules
Cations
Anions
Contain two or more elements with fixed mass percents
Covalent:
Glucose: 40.00% C
6.71% H
53.29% O
Ionic:
Sodium chloride: 39.34% Na
60.66% Cl
Information in a Chemical Formula
Ca(NO3) 2
Calcium atom
Nitrate group: two nitrate groups
Per each calcium atom
Total elements: 1 Ca
2 N
6 O
Is the energy available but not being used or is it in use?
Types of Energy
Forms of Energy
Kinetic Energy (Motion Energy)
Radiant (light)
Thermal (heat)
Energy
Chemical
(Capacity to do work)
Potential Energy (Stored Energy)
Electrical
Mechanical
Law of Conservation of Energy:
In any chemical or physical change, energy can be converted from one form to another, but it is neither created nor destroyed
Units of Energy:
Joule :
Amount of kinetic energy possessed by a 2kg object moving at a speed of 1m/s. Substituting these values in the equation that defines kinetic energy:
Equivalent to the amount of energy you will
feel if you drop 4.4 lb from about 4 in. onto your foot.
calorie (cal) :
Amount of heat energy needed to raise the temperature of one gram of water by one degree Celsius measured between 14.5 and 15.5°C.
1 cal = 4.3184 J
The joule and calorie are rather small units.
The large calorie (Cal, C) is used to express the energy content of foods.
1kcal = 4.3184kJ
1C = 1kcal = 103 cal
140,000 cal of energy is released when the soft drink is metabolized within the body.
Sprite™ contains 140 C:
1 BTU (British Thermal Unit):
Amount of heat needed to raise the temperature of a lb of water one °F
1BTU =.818 kcal
Heat Capacity and Specific Heat
Joseph Black (~1750):
“Amount of heat needed to raise the temperature of a substance by the same amount depends on the substance”
Amount of heat needed to raise the temperature of a given quantity of substance in a specific physical state.
Heat Capacity
Amount of heat needed to raise the temperature of 1 g of a substance in a specific physical state by 1°C
Specific Heat
The specific heat of a substance changes when the physical state of the substance changes
Ex.
Water (ice)
Water (liquid)
Water (steam)
2 .1 J / g °C
4 . 18 J / g °C
2 . 0 J / g °C
The higher the specific heat of a substance, the less its temperature will change when it absorbs a given amount of heat.
At the beach, sand has a lower specific heat than water, so it heats up while water stays cool.
Heat transferred = mass x Specific heat x ∆T
q = m x Cs x ∆T
Amount of heat energy needed to cause a fixed amount of a substance to undergo a specific temperature change without causing a change of state.
Transfer of heat from one body to another.
Heat always flows from the warmer body to the colder body.
The heat loss by the warmer body is equal to the heat gained by the colder body.
Generalizations:
Potential energy
H2
H2
O2
O2
+
+
time
time
Heat in Chemical Change
Electrolysis
Direct synthesis
H2O
H2O
Potential Energy Diagrams