Welcome to
AP Chemistry
Scientific method
• A logical way of solving problems
• Three steps
– Making observations
– Formulate hypothesis
– Perform experiments
• Hypothesis is an educated guess (possible
explanation)
• Experiment is designed to test hypothesis
and leads to new observations
Scientific method
• After many cycles, a broad, generalized
explanation is developed for why things
behave the way they do (Theory explains
why)
• Also regular patterns of how things
behave the same in different systems
emerges (Law explains how)
• Laws are summaries of observations
Observations
Hypothesis
Theory
(Model)
Modify
Experiment
Prediction
Law
Experiment
Metric System
• Every measurement has two parts
– Number
– Unit
• SI system (le Systeme International) is
based on the metric system
• Prefix + base unit (Prefixes found on p.
10)
– Prefixes are based on powers of 10
Mass and Weight
• Mass is measure of resistance to
change in motion
• Weight is force of gravity
• Sometimes used interchangeably
• Mass can’t change, weight can
Uncertainty of Measurement
• Basis for significant figures
– All measurements are uncertain to some
degree
• Precision is how repeatable the
measurement is
• Accuracy is how close to true value.
• Random error - equal chance of being
high or low- addressed by averaging
measurements (It is expected)
Uncertainty of Measurement
• Systematic error- same direction each
time
• Better precision implies better accuracy
– Precision can occur without accuracy
– Accuracy cannot occur without precision
Significant figures
• All measurements have some degree of
uncertainty
• Exact numbers are counted, have
unlimited significant figures
• If it is measured or estimated, it has sig
figs.
• All numbers except zero are significant.
• Some zeros are significant, some aren’t
Which zeroes count?
• In between other sig figs, zeros count
• Before the first non-zero, zeros don’t
count
• After the last number, zeros count if
it is after the decimal point
• 3200
2 sig figs
• 3200.
4 sig figs
Sig fig math
• In multiplication and division, the
answer must have the same number of
sig figs as the number with the least sig
figs in the problem.
• In addition and subtraction, same
number of decimal places must be used
in the answer as the number with the
fewest sig figs.
Dimensional Analysis
•
•
•
•
Use conversion factors to change units
Conversion factors = 1 (ALWAYS!)
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.
•
•
•
•
Examples
11 yards = 2 rod
40 rods = 1 furlong
8 furlongs = 1 mile
The Kentucky Derby race is 1.25 miles. How
long is the race in rods, furlongs, meters, and
kilometers?
• A marathon race is 26 miles, 385 yards.
What is this distance in rods, furlongs,
meters, and kilometers?
• The speed of light is 3.00 x 108 m/s. How far
will a beam of light travel in 1.00 ns?
Temperature
• A measure of the average kinetic
energy
• Use three different temperature scales,
but all are talking about the same height
of mercury. (Celsius, Kelvin, Fahrenheit)
0ºC = 32ºF
0ºC
32ºF
100ºC = 212ºF
0ºC = 32ºF
0ºC 100ºC
212ºF 32ºF
100ºC = 212ºF
0ºC = 32ºF
100ºC = 180ºF
0ºC 100ºC
212ºF 32ºF
100ºC = 212ºF
0ºC = 32ºF
100ºC = 180ºF
1ºC = (180/100)ºF
1ºC = 9/5ºF
0ºC 100ºC
212ºF 32ºF
Density
•
•
•
•
•
Ratio of mass to volume
D = m/V
Useful for identifying a compound
Useful for predicting weight
An intrinsic property- does not depend
on the amount of the material
Density Problem
• An empty container weighs 121.3 g. Filled
with carbon tetrachloride (density 1.53
g/cm3 ) the container weighs 283.2 g.
What is the volume of the container?
Classification of Matter
• Pure substances have constant composition
– Elements cannot be broken into simpler
substances
– Compounds have constant composition and can
be broken down
• Separation
–Filtration removes a solid from a liquid
–Distillation uses heat to separate gases
–Chromatography uses the mobile phase (liquid or
gas) to remove from a stationary phase (solid)
substance