Download Matter and Measurement

Matter and Measurement
•Recognize elements, atoms, compounds and
molecules.
•Identify physical and chemical properties and
changes.
•Apply the kinetic molecular theory to the properties
of matter.
•Use metric units and significant figures properly.
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Matter
Solutions are
Homogeneous mixtures
Classifying Matter
Matter
Occupies Space
Heterogeneous Matter
Not uniform throughout
Homogeneous Matter
Uniform throughout
Solutions
Uniform but variable composition
Sand and dirt
is a
heterogeneous
mixture
Pure Substance
Fixed composition
Cannot be further purified
Elements
Cannot be divided into simpler substances
Compounds
Elements united in fixed ratios
Ionic
(salts)
Covalent
(molecules)
Molecules of
antifreeze
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Elements and Compounds
• Elements combine
chemically to form
compounds
• Compounds can be
either ionic (salts) or
covalent (molecules).
NaCl (ionic salt) is formed chemically from sodium and chlorine in a oxidationreduction reaction.
Covalent
molecules
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Physical Properties
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Intensive vs. Extensive Properties
• Extensive properties depend upon the amount of
substance present.
– Examples: Mass, volume, moles etc.
• Intensive properties do not depend upon the amount of
substance present.
– Examples: Density, color, melting point, etc.
– Most physical properties are intensive.
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Physical and Chemical Changes
•
•
•
In physical changes
the identity of the
substance is
preserved (no
chemistry).
In chemical changes a
new substance(s) is
produced (chemistry).
Physical changes
often occur with
chemical changes.
AMP_Chem 1A
Physical
change Napthalene melts.
Chemical
change - Formation
of water from its
elements.
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Kinetic Molecular Theory
• Matter consists of small particles - atoms or molecules.
• Matter has three physical states based upon temperature.
• Conversion between them is a physical process.
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Temperature
• Temperature is a
measure of
average kinetic
energy.
• 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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Numeric Information
• Be able to
recognize the SI
units.
• Memorize the
common metric
prefixes!
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Significant Figures
1.
2.
3.
4.
All nonzero digits are significant.
Zeroes between two significant figures are themselves
significant.
Zeroes at the beginning of a number are never significant.
Zeroes at the end of a number are significant if a decimal
point is written in the number.
Examples: 0.01000 has 4 significant figures
1.01000 has 6 significant figures
101000 has 3 significant figures
The last digit of a measured number is a.k.a the estimated digit
All digits are significant in an exact number. In a calculation between exact
numbers and measured numbers, we use the significant digits of the
measured number only.
Our class has 24 students. This is an exact number, as we can’t
have 24.1 students !!
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Significant Figures
• When addition or subtraction is performed, answers are
rounded to the least significant decimal place.
• When multiplication or division is performed, answers are
rounded to the number of digits that corresponds to the least
number of significant figures in any of the numbers used in
the calculation.
Example:
1.0035 X 10-10 + 9.047 X 10-8
Convert the exponentials to the same power. 1.0035 X 10-10 is
0.0010035 X 10-8
Then write the equation as: 0.010035 X 10-8 + 9.047 X 10-8
Ans: 9.057 X 10-8
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Accuracy versus Precision
•
The term significant figures refers to digits that were
measured.
•
We need to pay attention to them or we will
overstate the accuracy of the answer.
•
Accuracy refers to the proximity of a measurement
to the true value of a quantity.
•
Precision refers to the proximity of several
measurements to each other.
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Uncertainty in Measurements
Different measuring devices have different
uses and different degrees of accuracy
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Problem Solving Review - In class
Complete the following problems from your textbook:
1.24
1.31
1.45
1.51
1.63
1.67
1.70
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Chapter Summary
Section 1.4 Measurements in chemistry are made using the metric system. Special emphasis is placed
on a particular set of metric units called SI units, which are based on the meter, the kilogram, and the
second as the basic units of length, mass, and time, respectively. The metric system employs a set of
prefixes to indicate decimal fractions or multiples of the base units. The SI temperature scale is the
Kelvin scale, although the Celsius scale is frequently used as well. Density is an important property that
equals mass divided by volume.
Section 1.5 All measured quantities are inexact to some extent. The precision of a measurement
indicates how closely different measurements of a quantity agree with one another. The accuracy of a
measurement indicates how well a measurement agrees with the accepted or "true" value. The
significant figures in a measured quantity include one estimated digit, the last digit of the
measurement. The significant figures indicate the extent of the uncertainty of the measurement.
Certain rules must be followed so that a calculation involving measured quantities is reported with the
appropriate number of significant figures.
Section 1.6 In the dimensional analysis approach to problem solving, we keep track of units as we
carry measurements through calculations. The units are multiplied together, divided into each other, or
canceled like algebraic quantities. Obtaining the proper units for the final result is an important means
of checking the method of calculation. When converting units and when carrying out several other types
of problems, conversion factors can be used. These factors are ratios constructed from valid relations
between equivalent quantities.
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