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Chapter 1:Matter, Measurement, & Problem Solving
I) Introductory Questions...
1) Why study chemistry?
- Chemistry is everywhere!
- called The Central Science,chemistry serves as a bridge linking many scientific disciplines (e.g.,biology, medicine, pharmacy, physics, and engineering).
- Important to not only scientists, but other members of society
- Examples: Historian (carbon dating), Social Scientists (behavior), General Public (Environmental matters)
2) What is chemistry?
- Chemistry - the science that seeks to understand the behavior of matter by studying the behavior of atoms & molecules.
Chemists study the composition, properties and transformations of matter. In order to understand and fully appreciate matter, chemists need to be familiar with its structure, composition, and the changes that matter undergo.
- Matter - anything that has mass and occupies space. From this definition it is clear to see that chemistry is everywhere!
3) What are atoms & molecules?
- Atoms are submicroscopic particles that constitute the fundamental building blocks of matter.
Atoms function as our “chemistry alphabet” just like letters in a language.
Letters combine to form words; atoms are linked together by chemical bondsto form molecules.
letters words
atoms molecules
H, O H2Owater H, O H2O2 hydrogen peroxide
C, O COcarbon monoxide
C, O CO2carbon dioxide
Review Appendix IIA: Atomic colors (commit to memory)
- Molecules are two or more atoms joined in a specific geometric arrangement.
Words link to form sentences; molecules combine to form chemical reactions.
letters words sentences
atomsmolecules chemical reactions
4) Two Fundamental Core Concepts in Chemistry
- ALL matter is composed of various types of atoms (elements).
- One substance changes into another by reorganizing the way
atoms are attached to each other.
II) The Scientific Approach to Knowledge
1) What is the goal of science?
- The goal of science is to provide a framework for gaining and organizing knowledge.
2) How do scientists account for everything around us?
-Scientists use the scientific method to account for observed behavior.
-Although there is no “universal method” that is followed; it is generally agreed that the scientific method involves the following scheme.
Observation Hypothesis Experimentation
Theory Natural Law
3) The Scientific Method
- There are 3 stages to the scientific method
i)making observations
ii)formulating predictions (hypothesis)
iii)testing predictions by experimentation
- Observations (Two Types)
i)Qualitative– noting or describing how a process happens
ii)Quantitative – measuring or quantifying something about the process
-Hypothesis- tentative interpretation or explanation of the observations.
- Experimentation
i)Experiments are used to test (validate) hypothesis.
ii)Hypothesis must be reproducible and easily tested
- Theory
i)Theories are often called models; these terms are used interchangeably.
ii)Hypothesis that has survived numerous testing becomes a theory.
iii)Theory - set of tested hypothesis that gives an overall explanation of some natural phenomenon.
iv)Theories are always under scrutiny through new predictions and new experiments. If disproved, one must start again.
- Natural Law
i)A natural law is a statement that summarizes observable (measurable) behavior.
ii)Example: Law of Conservation of Matter
III) The Classification of Matter
1)Three states of matter we commonly encounter.
-Solids have fixed volume and rigid shape.
-Atoms & molecules vibrate but do not move.
-Subdivided into two classes (crystalline or amorphous) depending on arrangement of atoms or molecules.
-Examples include ice, diamond, salt, glass, charcoal, plastic, butter.
-Liquidshave fixed volume but variable shape.
-Molecules can move relative to each other.
-Examples include water, alcohol, gasoline.
-Gases have neither fixed volume nor definite shape.
-Gases are compressible and molecules can move freely.
-Examples are helium, nitrogen, air, and carbon dioxide.
2)Classifying Matter by Composition
-Pure Substances are comprised of only a single type of atom or molecule.
i) Pure substance has a constant composition
ii) Two types
Compounds: pure substance that is formed when atoms of two or more different elements combine in fixed, definite proportions.
- Compounds can be broken down into elements by chemical processes.
Elements: pure substances that can not be decomposed into simpler substances by physical or chemical means.
- Mixtures are comprised of two or more different types of atoms or molecules combined in variable proportions.
i) Mixtures have a variable composition
ii) Two varieties of mixtures
Homogeneous (solutions):1 phase only
Heterogeneous> 1 phase
iii) Mixtures can be separated into components using physical methods (decantation, distillation, filtration)
IV) Physical Chemical Changes and Physical & Chemical Properties
1)Physical changes result in alteration of state or appearance without changing the composition of a sample.
2)Chemical changes happen when the composition of a sample changes resulting in the formation of new substances.
3)Any characteristic that can be used to describe or identify matter is called a property. Size, odor, color, density, and solubility are examples.
4)Properties can also be classified as either physical or chemical.
A) Physical properties can be determined without changing the chemical composition of a sample. Examples are melting point, density, hardness, etc.
B) Chemical properties are those in which a given substance becomes a
NEW substance or substances with different properties & different compositions. Some examples include combustion of fuels, corrosion of metals, and electrolysis of water.
V) Energy: A Fundamental Part of Physical & Chemical Change
1)Physical and chemical changes are usually accompanied by energy changes.
2)Energy is defined as the capacity to do work or produce heat.
3)Work is the action of a force moving an object through a distance.
4)Total Energy of an object is sum of kinetic energy (energy of motion) and potential energy (stored energy associated with position or composition).
5)Thermal Energy is a type of kinetic energy; it is linked to the temperature of an object.
6)Law of Conservation of Energy states that energy is always conserved in a physical or chemical change; it is neither created nor destroyed.
7)Relationship between energy & stability reveals that nature favors systems that are lower in energy because they are more stable.
VI) Units of Measurement
1)Units are standard quantities used to specify measurements. Two components found in any quantitative scientific measurement
A) number (the value itself)
B) unit(describes information about the measured number)
Example: 8.01 has no meaning while 8.01 mL describes a volume
2) Units of measurement based on metric system (also called SI system)
3) SI system of measurement(Know Tables 1.1, 1.2, and 1.3)
A) 7 Fundamental SI units
i)The seven fundamental units are based on length, mass, time, temperature, amount of substance, electrical current, and luminous intensity (brightness).
B) All other units are called derived units, which are combinations of the fundamental units.
i)Examples of derived units include area (length)2, volume (length)3, and density (mass / volume)
4)SI prefixes & Scientific Notation
A) SI Prefixes allow one to express quantities in more manageable terms.
B) Scientific Notation allows one to conveniently express very large or small quantities. (see Appendix I for a review).
5) Measuring Quantities
A) Mass vs. Weight
i) mass - amount of matter contained in an object. (constant)
ii) weight - measure of force of attraction an object has for something else(not constant).
iii) SI unit for mass is the kilogram (1.00 kg = 2.205 lbs).
iv) Mass is measured using a balance and is typically expressed in grams (g), milligrams (mg), or micrograms (g).
B) Length
i) SI unit for length is the meter (1.00 m = 39.37 inches).
ii) Length is often expressed in centimeters (cm), millimeters
(mm), micrometers (m), nanometers (nm), and picometers (pm).
C) Temperature
i) Temperature is a measure of molecular motion; heat is associated with thermal energy transfer from hot to cold objects.
ii) Three temperature scales (Fahrenheit, Celsius, & Kelvin).
iii)SI unit for temperature is Kelvin
iv)Temperature Conversion Equations (subscript denotes temp. scale).
TK = TC + 273.15
TF = TC x (9F/5C) + 32 F
Practice Problem: Convert 98.6 F to Celsius & to Kelvin.
D) Volume
i) Volume is a derived unit and is an expression of the amount of space occupied by an object.
ii) SI unit for volume is the cubic meter (1 m3 = 264.2 gallons)
iii) In the laboratory volumes are expressed in cubic centimeters (cm3) or milliliters (mL). Note that 1 cm3 = 1 mL.
E) Density
i) Density is another derived unit that expresses an object’s mass per unit volume.
Density = (mass/volume)Typical Units: g/mL or g/cm3
ii) Density is a physical property for a substance and can be used to identify an unknown sample of matter. (see Table 1.4)
iii) Properties can be classified as either intensive or extensive, depending on whether their value changes with the size of the sample.
iv)Intensive properties, like density, melting point, and temperature, do not depend on sample size. Extensive properties, like mass, length and volume, do depend on sample size.
VII) Uncertainty in Measurement
1) All measurements carry some degree of uncertainty.
2) Depending upon measuring device, we can ascertain the certain digits along with the first uncertain digit. (We do this with every measurement taken)
Ex. Laboratory balance 4.875 g vs.4.8748 g
3) Precision vs. Accuracy
A) accuracy - how close a value is to “true value”
B) precision - degree of agreement among measurements of same quantity [Reproducibility]
4) Random vs. Systematic Errors
A) random (indeterminate) - error has equal chance of being high or low
(can not account or correct these errors)
B) systematic (determinate) - error occurs in same direction each time
(can control and minimize this error type)
5) Reporting Data “in the real world”
A) Average (Mean) of set of values Standard Deviation for data set
(accuracy) (precision)
VIII) Significant Figures
1) Counting Significant Figures
A) Non-zeros: Always significant
B) Zeros:
i) leading zeros:Never significant(0.00487 g)
ii) captive zeros:Always significant(4.063 km)
iii) trailing zeros:Sometimes significant
100 mLvs. 100. mL( 1 sf. vs. 3 sf.)
iv) can get around dilemma using scientific notation
- useful for handling very large or small values
- all values in mantissa are significant 1.00 x 102 mL
(see AppendixIA.)
C) Exact Numbers:Infinite number of significant figures
2) Calculations involving Significant Figures
A) Multiplication/Divisionvalue with least # sig. figs.
B) Addition/Subtractionlook for least # decimal places in calculation
C) Rounding Values
i) look at first non-significant (uncertain) digit ONLY
- If 5 or greater, round up preceding digit
- If < 5 leave alone
ii) DNRUD rule (DO NOT ROUND UNTIL DONE)
D) Examples
i) (12.56 x 4.236 ) / 3.64 = ?Answer = 14.6
ii)15.345 + 6.2257 + 4.31 + 9.4 = ?Answer = 35.3
IX) Dimensional Analysis
1) Factor Label Method(Unit Factor Method)
A) Conversion Factors - two equivalent quantities expressed as a fraction.
i) multiplying by “constant”
ii) allows one to go from one unit to another equivalent unit
iii) treated as exact factors
iv) UNITS GUIDE YOU TO ANSWER!!
B) Conceptual Plan (Concept Map) - visual outline that helps you see the general flow of the problem.
2) Examples(Review Example Problems in Text)
i) 6.50 ft tall man = ? cm tall
ii) 25.5 in wheel = ? cm wheel
iii) 10.0 km = ? miles
Answers:
6.50 feet x (12 inches / 1 foot) x (2.54 cm / 1 inch) = 198 cm
25.5 inches x (2.54 cm / 1.0 inches) = 64.8 cm
10.0 km x (1000 m/ 1.0 km) x (1.094 yd / 1 m) x (1 mile / 1760 yd) = 6.22 miles
Discussion Question #1:How many minutes in a month?
A) (1 yr / 12 mo.) x (365 days/yr) x (24 hrs./day) x (60 min/hr) = 43,800 min./month
B) (4 wks/mo) x (7 days/wk) x (24 hrs./day) x (60 min./hr) = 40,320 min./month
3) Two Items to Emphasize:
A) Conversion factors need to be chosen with care.
B) Conversion factors are exact values (infinite # sig. figs.).
X) Problem Solving Method
1) The Method
A) List Given Information with units (Read the problem carefully!)
B) Now place the Unknown (What you are trying to find?) quantity down with its units
C) Now one develops the strategy for solving the problem. To develop the concept plan usually involves obtaining relevant information, this may include
i) conversion factors (go from one set of units to another)
ii) physical constants or values found in reference tables
iii) equations needed to get to answer
D) Now it is time to solve the problem. Let the concept plan be your guide. Remember the power of units!
E) Lastly, perform the check step to see if answer has correct units and makes physical sense.