Measurement

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					      DO NOW….
      Which liquid has the highest density?
 least dense 1 < 3 < 5 < 2 < 4 most dense




                                         1

                                           3
                                           2                                 5   4

Coussement, DeSchepper, et al. , Brain Strains Power Puzzles 2002, page 16
•   Density is an                               Density
    INTENSIVE property
    of matter.
      - does NOT depend
        on quantity of matter.      Styrofoam       Brick



      -Examples:
       color, melting point, boiling point, odor, density

•   DIFFERENT THAN
    EXTENSIVE properties
      - depends on
        quantity of matter.
      - mass, volume, length
               Density
                             M
                         D =
                              V
    M    ass
                        M = DxV
                          V = M
D
ensity    V     olume

                              D
Density of Some
Common Substance
              Density of Some Common Substances

Substance                                          Density
                                                  (g / cm3)
 Air                                               0.0013*
 Lithium                                           0.53
 Ice                                               0.917
 Water                                             1.00
 Aluminum                                          2.70
 Iron                                              7.86
 Lead                                             11.4
 Gold                                             19.3
 *at 0oC and 1 atm pressure
                               Consider Equal Masses
                                                                              Equal masses…
                                                                              …but unequal volumes.
                                                                              The object with the
                                          aluminum                              larger volume
                                                                               (aluminum cube) has
                                                                               the smaller density.       gold




                                                                                                      Christopherson Scales




                                                                                                            Made in Normal, Illinois USA




Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 71
                 Comparing Densities (g/cm3)


                                                                                  cork
                                                                      0.25
                                                      0.9       ice



                                                                      water 1.0
                                                     aluminum
                                               2.7



Jaffe, New World of Chemistry, 1955, page 66
   Density Practice Problems
1. What is the density of carbon
   dioxide gas if 0.196 g occupies a
   volume of 100. mL?

                M
            D =
                V
     0.196 g
                 1.96 x 10-3 g/mL
    100. mL
   Density Practice Problems
2. An irregularly shaped stone has a
   volume of 5.0 mL. The density of
   the stone is 1.75 g/mL. What is
   the mass of this stone?

          M = DxV

     1.75 g/mL x 5.0 mL     8.8 g
   Density Practice Problems
3. A sample of iron has a mass of
   94 g and a density of 7.8 g/cm3.
   What is the volume of the iron?


          V = M
              D
        94 g
                    12 cm3
      7.8 g/cm3
Prefix   Symbol   Meaning           Exponential Notation
mega     M                  1,000,000
kilo     k                      1,000
hecto    h                        100
deka     da                         10
---      ---                          1
deci     d                            0.1
centi    c                            0.01
milli    m                            0.001
micro    µ                            0.000001
nano     n                            0.000000001


            Also know…
           1 mL = 1 cm3
                                            Practice Measuring

                                             0    1   2   3   4   5   4.5 cm
                                             cm




                                             0    1   2   3   4   5   4.54 cm
                                             cm




                                             0    1   2   3   4   5   3.0 cm
                                             cm

Timberlake, Chemistry 7th Edition, page 7
20




     15.0 mL


 15 mL ?




10
             Practice Recording Temperature
    60oC                     (Celcius)

                                             100oC
                     25oC
    50oC


                                             80oC
                     20oC
    40oC


                                             60oC
                     15oC
    30oC


                                             40oC
                     10oC
    20oC


                                             20oC
                     5oC
    10oC


                                             0oC
                     0oC
    0oC                                  E
                C   18.0oC                   60.oC
A   30.0oC
           Scientific Notation
  Calculating with scientific notation

        (5.44 × 107 g) ÷ (8.1 × 104 mol) =

 Type on your calculator:

 5.44    EE    7                  ÷                  8.1                  EE             4   =


= 671.6049383 = 670 g/mol = 6.7 × 102 g/mol
               Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
        Scientific Notation

       65,000 kg  6.5 × 104 kg
 Converting into scientific notation:
   Move decimal until there’s 1 digit to
    its left. Places moved = exponent.
   Large # (>1)  positive exponent
    Small # (<1)  negative exponent
   Only include sig. figs.
            Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
      Scientific Notation
      Practice Problems
2,400,000 g                                                 2.4                  10 6   g
0.00256 kg                                                   2.56                  10 -3   kg
7  10-5 km                                                  0.00007 km
6.2  104 mm                                                 62,000 mm
         Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
             Percent Error

  Indicates accuracy of a measurement


            experimental  accepted
% error                                                                                100
                                     accepted

      your value
                                              real value
             Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
              Percent Error
 A student determines the density of a
  substance to be 1.40 g/mL. Find the %
  error if the accepted value of the density
  is 1.36 g/mL.
              1.40 g/mL  1.36 g/mL
  % error                                                                               100
                                      1.36 g/mL

     % error = 2.94 %
              Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
        Significant Figures
 Counting Sig Figs

 All digits are significant EXCEPT…
   Leading zeros -- 0.0025
   Trailing zeros without
    a decimal point -- 2,500



            Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
        Significant Figures
 Calculating with Sig Figs (con’t)
   Exact Numbers do not limit the # of sig
    figs in the answer.
      Counting            numbers: 12 students
      Exact   conversions: 1 m = 100 cm




           Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
        Significant Figures
 Calculating with Sig Figs
   Multiply/Divide - The # with the fewest
    sig figs determines the # of sig figs in
    the answer.
(13.91g/cm3)(23.3cm3) = 324.103g
     4 SF                            3 SF
                                                                                      3 SF

                                                                                  324 g
            Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
   Significant Figures
    Practice Problems
(15.30 g) ÷ (6.4 mL)
   4 SF                                      2 SF

  = 2.390625 g/mL  2.4 g/mL
                                                                                    2 SF
  18.9 g
 - 0.84 g
  18.06 g  18.1 g
          Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Significant figures: Rules for zeros
    Leading zeros are not significant.
   Leading zero     0.421 – three significant figures


    Captive zeros are significant.
   Captive zero     4012 – four significant figures


    Trailing zeros are significant.
   Trailing zero    114.20 – five significant figures
                                           Rules for Counting Significant Figures

                    1. Nonzero integers always count as significant figures.
                    2. Zeros: There are three classes of zeroes.
                    a.       Leading zeroes precede all the nonzero digits and DO NOT count as
                                                                       2
                             significant figures. Example: 0.0025 has ____ significant figures.

                    b.       Captive zeroes are zeroes between nonzero numbers. These always
                                                                               4
                             count as significant figures. Example: 1.008 has ____ significant figures.

                    c.       Trailing zeroes are zeroes at the right end of the number.

                             Trailing zeroes are only significant if the number contains a decimal point.
                                                         3
                             Example: 1.00 x 102 has ____ significant figures.

                             Trailing zeroes are not significant if the number does not contain a decimal
                                                          1
                             point. Example: 100 has ____ significant figure.

                    3.       Exact numbers, which can arise from counting or definitions such as 1 m
                             = 100 cm, never limit the number of significant figures in a calculation.

Ohn-Sabatello, Morlan, Knoespel, Fast Track to a 5 Preparing for the AP Chemistry Examination 2006, page 53

				
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