Chemistry: The Study of Change
Lecture 2 of x, Chapter 1
1
Activity 1
More Properties and SI Units
2
Properties of Matter
Physical Property
Chemical Property
No change in
composition of matter
Yes their is a change in
composition
Examples: color, mp,
fp, and bp
H2 burns in air to
form water
What are the physical
properties of water?
3
Measurable Properties
• How does an intensive property differ from an
extensive property? Which of the following properties
are intensive and which are extensive? (a) length, (b)
volume, (c) temperature, (d) mass and (e) density.
• What devices are used for mass, volume, and
temperature?
4
Name That Unit!
• Numerical measurements and calculations are
meaningless with units
• International System of Units (SI)
?
5
Modifying SI Units
• Write the numbers represented by the following
prefixes: (a) mega-, (b) kilo-, (c) deci-, (d) centi-, (e)
milli-, (f) micro-, (g) nano-, (h) pico-
6
Calculating Density
• What units do chemists normally use for density of
liquids and solids? For gas density? Explain the
differences.
• Density (d) = mass/volume = m/V
• solids and liquids = g/mL or g/cm3
• gases = g/L
• Useful units of volume:
• 1 mL = 1 cm3
• 1000 mL = 1000 cm3 = 1L
7
Example Problem
• Gold is a precious metal that is chemically
unreactive. It is used mainly in jewelry, dentistry,
and electronic devices. A piece of gold ingot with a
mass of 301 g has a volume of 15.6 cm3. Calculate
the density of gold.
8
Converting Temperatures
• What are the 3
temperature scales?
• Give there symbols.
9
Example Problem, 1.24
• Normally the human body can endure a temperature of
105oF for only short periods of time without permanent
damage to the brain and other vital organs. What is this
temperature in degrees Celsius?
What units are used to report
local temperatures on the news?
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Activity 2
Handling Large and Small Numbers
11
Scientific Notation
• When do you use scientific notation?
• Example: mass of one H atom =
0.00000000000000000000000166 g or 1.66 x 10-23 g
• All numbers can be represented as N x 10n
• What is N and n?
• Express 568.762 in scientific notation?
• Moving decimal (•) rule:
•
+n
left
-n
right
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Adding and Subtracting
First, both numbers (N1 and N2) must have same exponent (n).
N1 + N2 or N1 - N2
Keep exponent (n) same.
(4.31 x 104) + (3.9 x 103) = (4.31 x 104) + (0.39 x 104)
= 4.70 x 104
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Multiplying and Dividing
Simply N1 × N2 or N1 ÷ N2
n1 + n2
n1 - n2
(4.0 x 10-5) x (7.0 x 103) = (4.0 x 7.0) (10-5+3)
= 28 x 10-2
= 2.8 x 10-1
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Example Problem, 1.32
• Express the answers to the following calculations in
scientific notation:
• (a) 0.00095 - (8.5 x 10-3)
• (b) 653 ÷ (5.75 x 10-8)
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Activity 3
Remembering Significant Figures
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Determining Sig. Figs.
• What are significant figures?
• Significant Figure Rules!
• Any digit that is not zero is significant. How many
sig. figs. are in 845 cm?
• Zeros between nonzero digits are significant.
40,501 kg?
• Zeros to the left of the first nonzero digit are not
significant. 0.08 L?
17
Determining Sig. Figs.
• More Significant Figure Rules
• If a number is > 1, then all zeros written to the right
of the decimal point are significant. How many sig.
figs. are in 2.0 mg?
• If a number is < 1, only zeros after or between
nonzero digits are significant. 0.3005 L?
• For numbers without decimals, zeros after the last
nonzero digit may or may not be significant.
400 cm?
18
Practice Exercise, 1.4
• Determine the number of significant figures in each
of the following measurements
• (c) 0.0320 m3
• (d) 6.4 x 104 molecules
• (e) 560 kg
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Sig. Figs. in Calculations
• Addition and Subtraction
• The answer cannot have more digits to the right of
the decimal point than any of the original numbers.
89.332!
+!1.1!
90.432!
3.70!
-2.9133!
0.7867!
one significant figure after decimal point!
round off to ?!
two significant figures after decimal point!
round off to ?!
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Sig. Figs. in Calculations
• Multiplication and Division
• The number of sig. figs. in the result is set by the
original number that has the smallest number of sig.
figs.
4.51 x 3.6666 = 16.536366!
= ?!
3 sig figs!
6.8 ÷ 112.04 = 0.0606926 ! = ?!
2 sig figs!
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Rounding Rules
• If trailing numbers are < 5, don’t round up. Round 8.724
to 3 sig. figs.?
• If trailing numbers are > 5, round up. Round 8.727 to 3
sig. figs.?
• Exact numbers
• Exact numbers (25 students) and conversion factors (1 in
= 2.54 cm) should not be considered when determining
sig. figs.
6.64 + 6.68 + 6.70!
= 6.67333 = 6.67 ! = 7!
For multi-step calculations,
3!
avoid rounding errors by
waiting until the end to
round answers.
Because 3 is an exact number!
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Practice Exercise, 1.5
• Carry out the following arithmetic operations and
round off the answers to the appropriate number of
significant figures
• (b) 9.1 g - 4.682 g =
• (c) 7.1 x 104 dm × 2.2654 x 102 dm =
• (d) 6.54 g ÷ 86.5542 mL
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