Welcome to AP Chemistry

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

Scientific Method Theory (Model)Theory (Model)

– A set of tested hypotheses that give an overall A set of tested hypotheses that give an overall explanation of some natural phenomenon why things explanation of some natural phenomenon why things behave the way they dobehave the way they do

– explains why something happensexplains why something happens

LawLaw– The same observation applied to many different The same observation applied to many different

systemssystems– Example - Law of Conservation of Example - Law of Conservation of MassMass

Laws are summaries of observationsLaws are summaries of observations

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

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 aren’t

Which zeroes count?

ZerosZeros

leading zerosleading zeros

captive zeroscaptive zeros

trailing zerostrailing zeros

3200 2 sig figs

3200. 4 sig figs

Which zeroes count?

ZerosZeros

Captive zerosCaptive zeros always count always count as significant figures. as significant figures.

16.07 16.07 hashas

4 4 sig figs.sig figs.

Which zeroes count?

ZerosZeros

Trailing zerosTrailing zeros are significant are significant

only if the number containsonly if the number contains

a decimal point.a decimal point.

9.3009.300 has has

44 sig figs. sig figs.

Which zeroes count?

Exact numbersExact numbers have an infinite have an infinite number of significant figures.number of significant figures.

11 inch = inch = 2.54 2.54 cm, exactlycm, exactly

Doing the mathMultiplication and division

# sig figs in the result equals the # sig figs in the result equals the number in the least precise number in the least precise measurement used in the calculationmeasurement used in the calculation

6.38 6.38 2.0 = 2.0 =

12.76 12.76 13 (2 sig figs)13 (2 sig figs)

Doing the mathAddition and subtraction

# sig figs in the result equals the # sig figs in the result equals the number of decimal places in the least number of decimal places in the least precise measurement.precise measurement.

6.8 + 11.934 =6.8 + 11.934 =

22.4896 22.4896 22.5 (3 sig figs)22.5 (3 sig figs)

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

The Fundamental SI Units

Prefixes giga- G 1,000,000,000 109

mega - M 1,000,000106

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

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 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.

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 can’t have accuracy without precision

Dimensional Analysis

Using the units to solve problems

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.

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

Temperature A measure of the average kinetic

energy Different temperature scales, all are

talking about the same height of mercury.

100ºC 212ºF

100ºC =212ºF

0ºC 32ºF

0ºC = 32ºF

Temperature

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