Chapter 1: Keys to the Study of Chemistry
Chemistry is the study of matter,
its properties,
the changes that matter undergoes,
and
the energy associated with these changes
The topics in this chapter should be review
from a previous course. It is expected that
you are able to review and master this
material quickly and somewhat independently.
From this Chapter you should:
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understand the basics of the Scientific Method.
be able to identify physical and chemical properties and changes.
be able to apply the kinetic molecular theory to the properties of matter.
develop proficiency with metric units and dimensional analysis.
know the meaning of the terms precision and accuracy.
be able to use significant figures properly, understanding how they
relate to uncertainty in measurements.
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The Scientific Method
The scientific method provides guidelines for the practice of
science.
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Collect data (observe, experiment, etc.).
Look for patterns.
Try to explain data; develop a hypothesis or tentative explanation.
Test hypothesis, then refine/revise the hypothesis if experimental
results do not support it.
Bring information together into a scientific law (natural law), a
concise statement or mathematical equation that summarizes or
describes the behavior of matter.
Bring hypotheses and laws together into a theory. A theory explains
what causes certain phenomena and can be used to make predictions.
A theory must have considerable evidence or facts to support it.
Test predictions based on theory. Modify theory if if experimental
results do not support it.
Test Theory
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Definitions
(These you should already know!)
Matter
Composition
Properties
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Physical and Chemical Changes/Properties
Each pure substance has a unique set of physical and chemical properties
that can be used to identify it. These you should already understand!
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Give some examples of
physical properties:
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In physical changes the
identity of the substance
is preserved.
Examples?
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Give some examples of
chemical properties:
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In chemical changes new
substances are produced,
the identity of the
substance changes.
Examples?
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Physical
change Napthalene
melts.
Chemical
change Formation of
water from its
elements.
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The States of Matter
(These you should already know!)
Solid
Liquid
Gas
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Energy in Chemistry
Energy is the ability to do work.
Potential Energy
Kinetic Energy
Total Energy = Potential Energy + Kinetic Energy
Energy is conserved. (First Law of Thermodynamics)
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Potential Energy Between Charged Particles
(a fundamental concept in understanding chemistry)
Lower energy states are more
stable and are favored over higher
energy states.
Energy can be converted from one
form to another, but the total energy
is conserved.
A system of oppositely charged particles. The potential energy
gained when the charges are separated is converted to kinetic energy as
the attraction pulls these charges together.
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Chemical Potential Energy Converted to Kinetic Energy
(a fundamental concept in understanding chemistry)
A system of fuel and exhaust. A fuel is higher in chemical
potential energy than the exhaust. As the fuel burns, some of its
potential energy is converted to the kinetic energy of the moving
car and to heat energy that is lost to the surroundings.
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Kinetic Molecular Theory
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Matter consists of small particles; atoms, molecules or ions that are in
constant, random motion.
As temperature increases, the average kinetic energy of the particles
increases and the motion becomes more rapid.
HEAT FLOW:
Matter has three physical states. Physical state depends upon the nature of
the substance (its identity), its temperature and the pressure exerted upon
the substance. As chemists we describe these states at either the
macroscopic level or microscopic (particulate) level.
Conversion between these states is a physical process.
Solid
Liquid-solid
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Solid-gas
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Temperature
• Temperature is a
measure of average
kinetic energy of
the particles within
matter.
• We will use the Kelvin
(K) and Celsius scales
(°C).
• Be able to convert
between them:
K = °C + 273.15
°C = K - 273.15°
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Kinetic Molecular Theory and Physical State
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Intensive vs. Extensive Properties of Matter
• Extensive properties:
– Examples?
• Intensive properties:
– Examples?
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Units of Measurement
Know the SI units of mass, length,
time, temperature, and amount of
a substance.
Table 1. 2
SI Base Units
Physical Quantity
(Dimension)
Unit Name
Unit Abbreviation
Mass
kilogram
kg
Length
meter
m
Time
second
s
Temperature
kelvin
K
Electric Current
ampere
Amount of substance
mole
Luminous intensity
candela
Know the most common metric prefixes!
(mega, kilo, deci, centi, milli, micro, nano
and pico)
Table 1.3
Common Decimal Prefixes Used with SI Units
A
mol
cd
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Derived Units of Measurement
Formed using the SI base units. For example, velocity is distance
traveled per unit time, thus m/s.
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Volume
• Density
Table 1.5
Densities of Some Common Substances*
Substance
Physical State
Density (g/cm3)
Hydrogen
gas
0.0000899
Oxygen
gas
0.00133
Grain alcohol
liquid
0.789
Water
liquid
0.998
Table salt
solid
2.16
Aluminum
solid
2.70
Lead
solid
11.3
Gold
solid
19.3
*At
room temperature (20°C) and normal atmospheric pressure (1atm).
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Other Derived Units
Give the derived SI units for each of the following quantities in
base SI units:
a) acceleration = distance/time2
b) force = mass × acceleration
c) work = force × distance
d) pressure = force/area
e) energy = mass x (velocity)2
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Uncertainty and Errors in Measurements:
Accuracy and precision are two very different concepts. You are
expected to have a complete understanding of these!
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Accuracy:
Systematic Error:
Percent Error (MEMORIZE FORMULA!):
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Precision:
Random Error:
Significant Figures:
Range (MEMORIZE FORMULA):
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Significant Figures, Precision and Device
Every measurement includes some uncertainty. The rightmost digit of
10-mL Graduated Cylinders any measured quantity always contains some random error and is
estimated. For graduated glassware, the estimated digit is dependent
on the scale. For digital devices (thermometers and balances), the
estimated digit is the last digit shown on the read out and ALL digits
should be recorded, unless directed otherwise.
The number of significant figures in a measurement, such as 52.8 mL
for the 100-mL graduated cylinder shown below, is equal to the number
of digits that are known with confidence (5, and 2) plus the last digit (8),
which is an estimate or approximation. The measuring device used
determines which digit is estimated, and thus the precision of the
measurement.
Analytical Balance
100-mL Graduated Cylinder
Estimate the level of the liquid between
52 and 53 mL. This estimated digit is
the last digit that should be recorded.
200-mL Beaker
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Example: Sig Figs and Precision vs Accuracy
Three students each weigh a dry 50-mL graduated cylinder, add 25.0 mL of
water to the cylinder, and then weigh the cylinder plus water. The difference in
the masses is calculated to give a measured mass of the water in the cylinder.
All students use the same cylinder and same balance. Each student performs
this operation four times.
Student A’s Trial 1 data is as follows:
Mass of dry cylinder:
Mass of cylinder plus water:
110.0 g
135.2 g
What is the measured mass of the water in the cylinder for this trial? Report
answer with the correct sig. figs.
If the density of the water is 1.000 g/mL at the temperature of the experiment,
what is the actual mass of 25.0 mL of water? (Use correct sig. figs. in your
answer.)
The tables and graphs that follow on the next page summarize the results of
the measurements for each student.
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Example: Sig Figs and Precision vs Accuracy
Trial
Number
Water Mass
(g)
Trial
Number
Water Mass
(g)
Trial
Number
Water Mass
(g)
1
25.2
1
27.0
1
23.9
2
25.1
2
26.8
2
26.5
3
24.8
3
26.8
3
25.7
4
24.9
4
27.1
4
24.0
Average
25.0
Average
26.9
Average
25.0 g
Range
Range
Range
% Error
% Error
% Error
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Unit ConversionsDimensional Analysis
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English <—> Metric (Conversion factors provided)
Metric <—> Metric (Must know pico through Mega)
Ratios
Sequential
Converting squared and cubed units
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Questions and Problems
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Small spheres of equal mass are made of lead (density = 11.3 g/cm3),
silver (10.5 g/cm3), and aluminum (2.70 g/cm3). Which sphere has the
largest diameter, and which has the smallest? Clearly explain how you
came to your conclusion.
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The anesthetic procaine hydrochloride is used during dental surgery. It
is packaged as a 10.0% solution by mass in water. The density of the
solution is 1.1 g/mL. If a dentist injects 0.50 mL of the solution into a
patient, what mass of procaine hydrochloride is injected?
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Questions and Problems
• Suppose you build a planter box for growing vegetables in your back yard and
you want to determine the amount of soil needed to fill the box to within 2.0
cm from the top. You measure the box to be 3.10 m long, 1.52 m wide and
50.0 cm high. When you go to Orchard Supply to order the soil, you discover
that garden soil is sold by the cubic yard at a cost of $35.00 per cubic yard.
Being highly skilled in unit conversions, you confidently calculate the amount
of soil needed in cubic yards. How many cubic yards do you decide to order
and what will be the total cost?
• In the 2012 London Olympics, Michael Phelps won a gold medal in the 100 m
butterfly with a time of 51.21 seconds. What was his average speed in miles
per hour? (Assume that the uncertainty in the distance is ±0.1 m.)
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Questions and Problems
• Gold can be hammered into extremely thin sheets called gold leaf. If a
200-mg piece of gold (density = 19.32 g/cm3) is hammered into a sheet
measuring 2.4 ft × 1.0 ft, what is the average thickness of the sheet in
meters?
How might the thickness be expressed without exponential notation,
using an appropriate metric prefix?
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