Foundations of Chemistry

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Foundations of Chemistry
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Prefixes

• Tera- T 1,000,000,000,000 1012
• 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- m 0.000001 10-6
• nano- n 0.000000001 10-9
• pico- p 0.000000000001 10-12

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Prefixes

• Tera- T 1,000,000,000,000 1012
• 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- m 0.000001 10-6
• nano- n 0.000000001 10-9
• pico- p 0.000000000001 10-12

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Mass

• is the amount of matter in an object.
• Tool - balance scale
• Standard SI unit kilogram
• Base unit - gram
• Common units mg,mg, g, kg
• Weight pull of gravity on matter

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Length

• The distance between two points
• Tool metric ruler
• Standard unit - meter
• Common units mm, cm, m, km

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Derived Units

• Many SI units are combinations of base units
  called derived units
• Examples we will use at this time are volume and
  density

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Volume

• The amount of space an object occupies
• V L x W x H
• Tools metric ruler, graduated cylinder, buret,
  volumetric flask
• SI unit - m3
• 1 Liter 1 dm3
• 1 mL 1 cm3 1 cc

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Using Scientific Measurements

• All measurements have a certain degree of
  uncertainty
• Uncertainty can result in limitations that depend
  on the instrument or the experimenter
• Scientists use two word to describe how good the
  measurements are

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How good are the measurements?

• Accuracy- how close the measurement is to the
  actual value
• Precision- how closely the numerical values of a
  set of measurements agree with each other
• Random error - equal chance of being high or low-
  addressed by averaging several measurements
• Systematic error- same direction each time, they
  can be compensated for

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Percent Error

• Accuracy is judged using percent error.
• The formula is
• Actual Value Experimental Value x 100
• Actual Value

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Significant figures (sig figs)

• Scientists record measurements in significant
  figures.
• Sig figs consist of all the digits known with
  certainty plus a final digit that is estimated.

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Rules for Determining Sig Figs

• All nonzero digits are significant
• Exact numbers (from counting or definitions) do
  not limit sig figs
• All zeros between nonzero digits are significant

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Atlantic/Pacific Rule for Determining Sig Figs

• If a decimal point is Present, count from the
  Pacific side
• If a decimal point is Absent, count from the
  Atlantic Side
• Begin counting with the first nonzero digit you
  come to and then keep counting

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Adding and subtracting with sig figs

• Round the answer so that the estimated digit is
  in the same place value as the least precise
  measurement

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For example

• First line up the decimal places

Then do the adding
Find the estimated numbers in the problem
34.33
This answer must be rounded to the tenths place
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Multiplication and Division

• The answer should have the same number of
  significant figures as the measurement with the
  least number of sig figs
• 3.6 x 653
• 2350.8
• 3.6 has 2 s.f. 653 has 3 s.f.
• answer can only have 2 s.f.
• 2400

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Dimensional Analysis

• A problem solving method that treats units in
  calculations as algebraic factors
• Units common to both numerators and denominators
  are cancelled and removed from the expressions
• A conversion factors is used to convert from one
  unit to the other
• Exact conversions do not limit significant
  figures

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Density

• D M / V
• An intensive property (it is unaffected by the
  size of the sample)
• Density is often used to identify substances.
• Common units - g/ cm3, g/mL, g/L
• Tools? -

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Density

• As the mass of the substance increases the volume
  increases proportionately and the ratio of mass
  to volume (density) is constant
• This is a direct proportion therefore the graph
  is a straight line that passes through the
  origin.

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Density

• Because most substances expand with an increase
  in temperature (increasing the volume), density
  usually decreases with increasing volume.
• Density varies with temperature

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Density of water

• 1 g of water is 1 mL of water.
• density of water is 1 g/mL (at 4ºC)
• Specific gravity - the density of an object
  compared to the density of water
• Specific gravity of water is 1.0

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Chem II Quick Lab

• Use the accepted density to determine the
  thickness of aluminum foil.
• Compare your data and calculations with other
  students to concur and determine an average.Write
  a short lab report in your composition book that
  includes a data table.
• D m/V
• D m/ LWH
• H m/DWH

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Temperature

• A measure of the average kinetic energy
• Different temperature scales based on the same
  expansion of mercury.
• So why are they different?

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Converting Between Celsius and Kelvin
K C 273.15 C K - 273.15
273K
0ºC
100 º C 373K
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Converting Between Celsius and Fahrenheit 1ºC
9/5ºF F 9/5ºC 32 C 5/9 (ºF 32)
0ºC
100ºC
212ºF
32ºF