Welcome to AP Chemistry

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Welcome to AP Chemistry
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Scientific Method

• A method of solving problems/answering questions
• Observation- what is seen or measured
• Hypothesis- educated guess of why things behave
  the way they do. (possible explanation)
• Experiment- designed to test hypothesis
• leads to new observations,
• and the cycle goes on

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Scientific Method

• Theory (Model)
• A set of tested hypotheses that give an overall
  explanation of some natural phenomenon why things
  behave the way they do
• explains why something happens
• Law
• The same observation applied to many different
  systems
• Example - Law of Conservation of Mass
• Laws are summaries of observations

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Scientific Method

• Theories have predictive value.
• The true test of a theory is if it can predict
  new behaviors.
• If the prediction is wrong, the theory must be
  changed.
• Theory- why
• Law - how

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Significant Figures

• Meaningful digits in a MEASUREMENT
• Exact numbers are have unlimited significant
  figures
• If it is measured or estimated, it has sig. figs.
• All numbers except zero are significant.
• Some zeros are, some arent

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Which zeroes count?

• Zeros
• ? leading zeros
• ? captive zeros
• ? trailing zeros
• 3200 2 sig figs
• 3200. 4 sig figs

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Which zeroes count?

• Zeros
• ? Captive zeros always count as significant
  figures.
• 16.07 has
• 4 sig figs.

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Which zeroes count?

• Zeros
• ? Trailing zeros are significant
• only if the number contains
• a decimal point.
• 9.300 has
• 4 sig figs.

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Which zeroes count?

• Exact numbers have an infinite number of
  significant figures.
• 1 inch 2.54 cm, exactly

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Doing the math

• Multiplication and division
• sig figs in the result equals the number in the
  least precise measurement used in the calculation
• 6.38 ? 2.0
• 12.76 ? 13 (2 sig figs)

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Doing the math

• Addition and subtraction
• sig figs in the result equals the number of
  decimal places in the least precise measurement.
• 6.8 11.934
• 22.4896 ? 22.5 (3 sig figs)

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SI Measurement System

• Every measurement has two parts
• Number
• Scale (unit)
• SI system (le Systeme International) based on the
  metric system
• Prefix base unit
• Prefix tells you the power of 10 to multiply by -
  decimal system -easy conversions

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The Fundamental SI Units
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Prefixes

• giga- G 1,000,000,000 109
• mega - M 1,000,000 106
• kilo - k 1,000 103
• deci- d 0.1 10-1
• centi- c 0.01 10-2
• milli- m 0.001 10-3
• micro- ? 0.000001 10-6
• nano- n 0.000000001 10-9

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Mass and Weight

• Mass is measure of resistance to change in motion
  
• Weight is force of gravity.
• Sometimes used interchangeably
• Mass cant change, weight can

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Uncertainty

• A digit that must be estimated is called
  uncertain.
• A measurement always has some degree of
  uncertainty
• Basis for significant figures
• Precision- how repeatable
• Accuracy- how correct - closeness to true value.

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Uncertainty

• Random error - equal chance of being high or low-
  addressed by averaging measurements -
• expected in all measurements
• Systematic error- always the same direction each
  time
• you want to avoid this type of error
• you can have precision without accuracy
• You cant have accuracy without precision

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Dimensional Analysis

• Using the units to solve problems

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Dimensional Analysis

• Use conversion factors to change the units
• Conversion factors 1
• 1 foot 12 inches (equivalence statement)
• 12 in 1 1 ft.
  
  1 ft. 12 in
• 2 conversion factors
• multiply by the one that will give you the
  correct units in your answer.

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Examples

• Science fiction often uses nautical analogies to
  describe space travel. If the starship U.S.S.
  Enterprise is traveling at warp factor 1.71, what
  is its speed in knots?
• Warp 1.00 5.00 times the speed of light
• speed of light 3.00 x 108 m/s
• 1 knot 2000 yd/h exactly

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Temperature

• A measure of the average kinetic energy
• Different temperature scales, all are talking
  about the same height of mercury.

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100ºC 212ºF
0ºC 32ºF
0ºC
100ºC
212ºF
32ºF
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Temperature
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Density

• Ratio of mass to volume
• D m/V
• Useful for identifying a compound
• Useful for predicting weight
• An intensive property- does not depend on how
  much material there is