Regents Chemistry

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Regents Chemistry

• Chapter 1 The Science of Chemistry

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What is Matter?

• Matter is the stuff of which the universe is
  composed..and comes in three states
• Anything that has mass and occupies space is
  considered matter!

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Mixtures and Pure Substances

• A mixture is something that has variable
  composition.
• Example soil, cereal, air
• A pure substance will always have the same
  composition. Pure substances are elements or
  compounds.
• Example pure water, NaCl salt, carbon

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Mixtures

• For Example

Elements, which are pure substances. Can you
name one?
AIR
Compounds, which are pure Substances Can you
name one?
Mixture of oxygen nitrogen, carbon dioxide Argon,
water, others
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Elements and Compounds Pure substances have an
invariable composition and are composed of either
elements or compounds. Elements "Substances
which cannot be decomposed into simpler
substances by chemical means". Compounds Can be
decomposed into two or more elements.
For Example Electrolysis of Water
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Elements Elements are the basic substances out
of which all matter is composed.
Everything in the world is made up from only
110 different elements. 90 of the human
body is composed of only three elements
Oxygen, Carbon and Hydrogen Elements are
known by common names as well as by their
abbreviations (symbols).
Ne
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Elements early pioneers

• Robert Boyle (1627 1691) the first scientist
  to recognize the importance of careful
  measurements.
• Defined the term element in terms of
  experimentation
• a substance was an element unless it could be
  broken down into two or more simpler substances

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Compounds
Compounds are substances of two or more
elements united chemically in definite
proportions by mass. The observation that the
elemental composition of a pure compound is
always the same is known as the law of constant
composition (or the law of definite
proportions).For Example...
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Good Old H2O
For example, pure water is composed of the
elements hydrogen (H) and oxygen (O) at the
defined ratio of 11 hydrogen and 89 oxygen by
mass.
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Classification of Mixtures

• Homogeneous Mixtures are the same throughout (a
  single phase). ex table salt and water, air,
  brass
• Heterogeneous Mixtures contain regions that
  have different properties from those of other
  regions (more than 1 phase).
  ex sand in water, cereal

Phase - area of uniform composition
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Examples of Heterogeneous Mixtures

• Sand on a beach
• Cereal
• sand in water
• Dirt
• Most of the time you can see the different
  substances, hence the mixtures are said to be not
  well mixed and can be separated physically

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Examples of Homogeneous Mixtures, also called
Solutions

• Air
• Table salt in water
• Solution of Na2SO4
• You cannot see the different substances
• in the mixture (solution) - can be separated
  by chemical or physical means

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Identify each of the following..
End
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The SI System and SI Metric Math

• In 1960 a system abbreviated the SI system was
  introduced to provide a universal means to
  evaluate and measure matter. There are 7 base
  units

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Prefixes

• Base units can be too large or small for some
  measurements, so prefixes are added. See your
  reference table

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Scientific Notation

• In order to use this system, we must first
  understand scientific notation
• Why do we use it?

BIG THINGS
Very Small things...
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Scientific Notation

• What can the number 10 do?

It can be used as a multiplier or a divider to
make a number LARGER or smaller
Example 1.0 x 10 10 x 10 100 x 10
1000 AND Example 1.0 / 10 0.10 / 10
0.010 / 10 0.0010
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Scientific Notation

• Scientific notation uses this principle
• butuses a shorthand form to move the decimal
  point

The shorthand form is called THE POWERS OF 10
See Powers of 10 Animation
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The Powers of 10

• 1.0 x 10 x 10 100right?!
• 1.0 is multiplied twice by ten
• therefore 10 x 10 102

This is called an exponent and is written EE on
your calculator!
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The Powers of 10

• Overall..
• 1.0 x 10 x10 x 10 1.0 x 103 1000
• We can also look at it a different way..
• 1000 has three zeros after the digit 1..so..
• it takes three moves to the right to get to the
  end of the number!

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The Powers of 10
1 0 0 0
3 moves to the right gives a positive exponent
1.0 x 103 1000 also!
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Moves to the right make a number larger...

• But what about moves to the left?

1.0
The number gets smaller!
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Moves to the left

• 0.01 2 moves from 1.0 to the left
• therefore..
• 1.0 x 10-2

The negatives sign means move decimal to the
left!
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The Powers of 10 Summary

• Moves to the right are positive and
• make a number larger!
• Moves to the left are negative and
• make a number smaller!
• The number with the decimal gt 9.99..etc
• and cannot be smaller than 1.0

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Practice Problems

• Convert to Scientific Notation
• 10000
• 50000
• 565,000
• 0.0036
• 0.00000887

1 x 104
5 x 104
5.65 x 105
3.6 x 10-3
8.87 x 10-6
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Practice Problems

• Convert to regular numbers
• 2.3 x 105
• 5.3 x 103
• 6.75 x 10-4
• 3.19 x 10-9

230,000
5300
0.000675
0.00000000319
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Dealing with positive exponents
Count the moves and see!

• 3.0 x 105 also equals 300,000
• 300,000

number gets larger, so we need less of a
positive exponent to make an equal value
number gets smaller, so we need more of a
positive exponent to make an equal value
0.30 x 106
30.0 x 104
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Dealing with negative exponents

• 3.0 x 10-5 also equals 0.00003
• 0.00003

Count the moves and see!
number gets larger, so we need less of a
negative exponent to make an equal value We are
moving closer to the decimal point!
number gets smaller, so we need more of a
negative exponent to make an equal value. We are
moving further from the decimal point!
0.30 x 10-4
30.0 x 10-6
0.00003
0.00003
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Practice Problems
0.15 x 104

• 1.5 x 103 0.15 x 10?
• 2.0 x 105 200 x 10?
• 3.6 x 10-3 0.36 x 10?
• 5.5 x 10-5 5500 x 10?

200 x 103
0.36 x 10-2
5500 x 10-8
End
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Regents Chemistry

• Significant Figures

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Five-minute Problem

• How many significant figures are in the
  following (write the number and answer)
• 125
• 1.256
• 0.0000004567
• 0.00300
• 1.004623

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Significant FiguresWhy?

• Allow us to make an accurate measurement!
• Contain certain numbers
• and one uncertain number

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Certain Numbers

• Same regardless of who made the measurement
• Actual divisions marked on instrument
• Example Ruler, beaker

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Uncertain Numbers

• Are an estimate
• Vary by person and trial
• For example estimate with a ruler, beaker

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Significant Figures Include...

• All certain numbers and one uncertain number
• For example 8.55 cm is actually
• 8.55 0.01

-
The last digit is not actually on the ruler you
must make an estimate!
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Rules for Counting Sig. Figs.

• 1. Nonzero integers - always count
• ex 1322 has four significant figures
• 2. Zeros
• Leading Zeros - precede all nonzero digits
• and do not count! Ex 0.00025
• Captive Zeros - fall between nonzero digits
• and always count! Ex 1.008
• Trailing Zeros - zeros at end of number Ex. 100.
  vs. 100
• Significant only if the number contains a
  decimal

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Rules for Counting Sig. Figs.

• 3. Exact Numbers - have an unlimited
• amount of significant figures
• 2 Kinds
• Describe something50 cars, 25 bugs
• By definition 1 in 2.54 cm

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Rounding Numbers and Sig Figs

• Less than 5
• Equal to/more than 5

End
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Dimensional Analysis and conversions with the SI
System

• Given 1 in 2.54 cm
• Problem Convert 12.5 in to cm
• We use the parentheses method of DA

12.5 in
2.54 cm
31.75 cm
31.8 cm

1 in
But you must consider sig figs, so
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What about more than 1 conversion?

• Given 1 kg 103 g and 1?g 10-6 g
• Problem Convert 5 kg to ?g
• Two methods

103 10-6
equals
1 ?g
103 g
5 kg

3 - - 6 9
1 kg
10-6g
So your final answer is
5 x 109 ?g
You can simply use your calculator ? EE button
Learn the simple rules of math with scientific
notation
end