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![Page 1: 10/5/2015 An Introduction to Chemistry Chapter 1 Eugene Passer Chemistry Department Bronx Community College © John Wiley and Sons, Inc Eugene Passer Chemistry.](https://reader036.fdocuments.in/reader036/viewer/2022062718/56649e875503460f94b8ab26/html5/thumbnails/1.jpg)
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An Introduction to Chemistry Chapter 1
An Introduction to Chemistry Chapter 1
Eugene PasserChemistry DepartmentBronx Community College
© John Wiley and Sons, Inc
Eugene PasserChemistry DepartmentBronx Community College
© John Wiley and Sons, Inc
Version 1.0
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1.1 What is a Science?
The observation, identification, description, experimental investigation, and theoretical explanation of natural phenomena.
“the study in which humans attempt to organize and explain, in a sytematic and logical manner, knowledge about themselves and their surroundings”
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PHYSICAL SCIENCES:Astronomy, Geology, Physics, Chemistry
SCIENTIFIC DISCIPLINES
BIOLOGICAL SCIENCES:Botany, Zoology
TODAY:Biochemistry, Molecular Biology
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• Chemistry is sometimes describes as the study of the structure and behavior of matter.
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CHEMISTRY DISCIPLINES
Analytical – what and how much (analysis)
General – fundamental laws and concepts
Inorganic – substances that are not organic
Organic – carbon and hydrogen containing compounds
Physical – energy changes in chemical reactions, theoretical
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1.3 How chemists discover 1.3 How chemists discover things - The Scientic Methodthings - The Scientic Method
The observation, identification, description, experimental investigation, and theoretical explanation of natural phenomena.
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Natural Phenomena
experimentally investigate
theoreticallyexplain
observe
describeidentify
research
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SCIENTIFIC METHOD1.Observation2.Literature research3.Hypothesis 4.Experiment 5.Theory
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DefinitionsDefinitions
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Hypothesis: A tentative explanation of certain facts (observation) that can be tested through experimentation.
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Experiment: is conducting a controlled test to collect data to support or negate a hypothesis.
• Data from experiments are called FACTS• Experiments must be conducted under carefully
controlled conditions so that they can be reproduced over and over. This separates science from pseudo science.
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Law: Statement of natural phenomena to which no exceptions are known under the given conditions. A law is not an explanation.
Theory: a statement which explains what is observed that is supported with experimental evidence and is used to make predictions. (Mathematical models are frequently derived from a theory. At any time, a new experiment may be done that invalidates the theory.)
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(tentative explanation)
(explanation based on fact)
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Measurements are the data obtained from an
experiment
CH. 1.4 –MEASUREMENT and UNITS
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What’s wrong with this measurement?
55.5
MEASUREMENT (cont)
Always include a numerical value and a unit
55.5 km makes more sense!
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Measurements used in chemistry
length, volume, mass, time,
temperature, pressure,
concentration
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The Metric System of Units
Used in scientific work, even in the US
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Table 1.1
SI Units (standard metric units)
Quantity Base Unit Abbrev.
Length
Mass
Time
Temp
meter
kilogram
second
kelvin
m
kg
s
K
Amount mole mol
Symbol
l
m
t
T
n
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SI Unit Prefixes
mega- M 106
deci- d 10-1
centi- c 10-2
milli- m 10-3
Prefix Symbol Factor
micro- 10-6
nano- n 10-9
pico- p 10-12
kilo- k 103
BASE UNIT --- 100
giga- G 109
GR
EA
TE
R T
HA
N
ON
E
LE
SS
TH
AN
ON
E
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LENGTH (m)
• Meter is both the standard and base metric unit
• Other common length measurement:
1 mm
1 cm
1 km
10-2 m
10-3 m
103 m
0.001 m (1000 mm / 1 m) 0.01 m (100 cm / 1 m)
1000 m (0.001 km / 1 m)
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• Combination of base units. (e.g., length length length)
• Standard unit is m3
• Base unit is L
• Other common units: cm3, dL, mL, μL
• Other facts:
1 cm3 = 1 mL1 dm3 = 1 L
Volume
1000 L = 1 m3
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Mass
• Mass is the total quantity of matter in something.
• Determined by weight
what is weight????
• Standard unit is kg
• Base unit is g
• Other common units μg, mg, kg
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Temperature
• A measure of the intensity of heat.
• It does not depend on the size of the system.
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Temperature Measurement
• There are three temperature scales: Kelvin, Celsius and Fahrenheit.
• The SI unit of temperature is the Kelvin.
• In the laboratory, temperature is commonly measured with a thermometer in Celsius.
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Degree Symbols
degrees Celsius = oC
Kelvin (absolute) = K
degrees Fahrenheit = oF
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Exact and inexact numbers
• Exact numbers are “counting” numbers 7 days per week 12 equals one dozen “there are 32 students in this room”
• Measurements are always inexact
1.5 Reporting Values from 1.5 Reporting Values from MeasurementsMeasurements
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Inexact Numbers (measurements) contain ERROR
• Systematic – controllable (faulty equipment)
• Random - uncontrollable (noise)
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• Accuracy - how close a measurement is to the accepted value
• Precision - how close a series of measurements are to each other
ACCURATE = CORRECT
PRECISE = CONSISTENT
Accuracy and Precision
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Choose an answerChoose an answer
1. Accurate/precise
2. Accurate/imprecise
3. Inaccurate/precise
4. Inaccurate/imprecise
A) B)
C) D)
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Choose an answerChoose an answer
1. Accurate/precise
2. Accurate/imprecise
3. Inaccurate/precise
4. Inaccurate/imprecise
A)55.3 kg55.4 kg55.5 kg
B)
54.9 kg54.8 kg55.0 kg
C)
54.7 kg55.6 kg55.9 kg
D)
54.2 kg54.7 kg55.5 kg
AVG = 55.4 kg
AVG = 55.4 kg AVG = 54.9 kg
AVG = 54.8 kg
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Uncertainty in measurement
• Every measurement has error associated with it.
• The more precise the measurement the less error.
• Error in a measurement is indicated by the number of significant figures in the number
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• Which measurement has less error?
• Which measurement is more precise?
• Which measurement has more significant figures?
29.2oC or 29.25oC
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Significant Figures
• Indicate precision of a measurement.Sig. figs. do not apply to exact numbers
• Recording Sig FigsSig figs in a measurement include the known
digits plus a final estimated digit
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?.?? cm
?.?? cm
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Uncertainty in measurements
• Unless otherwise stated the last digit.
• Determined from the smallest division.• Stated on the device. E.g.: ± 1, ± 0.2, etc.
• The last digit in a digital display.
• Determined from the data set.
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Counting Sig Figs
• Count all numbers EXCEPT:
Leading zeros -- 0.0025
Trailing zeros without a decimal point -- 2,500
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4. 0.080
3. 5,280
2. 402
1. 23.50
Counting Sig Fig Examples
4 sig figs
3 sig figs
3 sig figs
2 sig figs