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Chapter 3: Scientific Measurement

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Qualitative observations using the 5 senses ... Measure using a graduated cylinder at the meniscus (the bottom of the curve) Units: mL or L ... – PowerPoint PPT presentation

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Title: Chapter 3: Scientific Measurement


1
Chapter 3 Scientific Measurement
  • A. Types of Measurements
  • Quantitative number and unit
  • counting or measuring
  • Qualitative observations using the 5 senses
  • - distinctive characteristics
    determine the specific make-up of a substance
  • In chemistry, we use both quantitative and
    qualitative types of analysis

2
  • B. Scientific Notation
  • Used to shorten really long numbers
  • General form _ . _ x 10exp
  • Positive exponent gt 1 (greater than)
  • Negative exponent lt 1 (less than)
  • Only when there is a negative sign in front of
    the first set of numbers is the number negative
    (a neg. exp. does not mean a neg. !)
  • ex. 3.6 x 103 is a pos. gt 1
  • 3.6 x 10-3 is a pos. lt 1 (but gt 0)
  • -3.6 x 103 is a neg.

3
  • Why use scientific notation?
  • ex. 3.6 x 103 3600. (decimal moves right)
  • 3.6 x 10-3 .0036 (decimal moves left)
  • -3.6 x 103 -3600
  • 6.02 x 1023 whoa mama!
  • 602000000000000000000000 (21 0s)
  • Practice these
  • ex. 3.17 x 107
  • 6.1 x 10-5
  • 1800000
  • 0.000482

31700000 0.000061 1.8 x 106 4.82 x 10-4
4
  • How do you plug scientific notation into the
    calculator for calculations?
  • Hit open parenthesis button (
  • Type in the decimal part _ . _
  • Hit the exponent button EXP or EE (this
    button means x 10) - no need to type x 10
  • Type in the exponent part
  • Hit the close parenthesis button )
  • Hit the operations button (, -, x, )

5
  • How to read the answer on the calculator?
  • Enter 3.62171 x 10-14 into the calculator
  • 3.62171E-14 3.6 x 10-14
  • 3.62171 x10-14 3.6 x 10-14
  • 3.62171 -14 3.6 x 10-14
  • Practice these
  • ex. (3.0 x 104) x (2.0 x 102)
  • (8.0 x 109) (2.0 x 104)
  • (3.6 x 1013) / (1.4 x 10-3)
  • (7.481 x 10-5) x (4.2 x 10-2)

6.0 x 106 4.0 x 105 2.6 x 1016 3.1 x 10-6
6
  • C. Significant Figures
  • Significant figures (sig figs) are the
    important numbers in a
  • Rules for rounding answers
  • Answers should be reported according to the least
    amount of decimal places in the data
  • ex. (7.481 x 10-5) x (4.2 x 10-2) 3.1 x 10-6
  • 3 decimals 1 decimal 1 decimal

7
  • Rounding to a decimal place
  • When you have more numbers in your calculator as
    an answer and you have to round to the correct
    number of sig figs
  • Look at the decimal place to the right of the
    last sig fig that you need to report
  • If the number is 5-9, you round up
  • If the number is 0-4, you round down (last number
    stays the same)

ex. 726.835 to 2 decimals 24.8514 to 3
decimals
726.84 24.851
8
  • Rules to determine sig figs from numbers
  • Every non-zero digit in a measurement is
    significant (ex. 24.7, 0.743, 714)
  • Zeros between non-zeros are significant (ex.
    7003, 40.79, 1.503)
  • Zeros to the left of non-zeros are not
    significant (ex. 0.0071, 0.42, 0.000099)

9
  • Rules (cont.)
  • Zeros at the end of a number (right of the
    decimal) are significant (ex. 43.00, 1.010)
  • Zeros at the end of a number (left of the
    understood not written decimal) are not
    significant (ex. 300, 7000, 27210)
  • Zeros at the end of a number (left of the
    decimal) are significant (ex. 300., 27210.)

10
  • Sig figs in measurements
  • Write down all known numbers, plus one extra
    number that is estimated
  • ex.

(a) 0.6 m 60 cm 600 mm
(b) 0.61 m 61 cm 610 mm
(c) 0.607 m 60.7 cm 607 mm
11
  • Precision vs. accuracy
  • Precision how close measurements are to
    each other (repeated trials)
  • Accuracy how close measurements are to
    the actual or accepted value
  • ex.

Precise but not accurate
Both precise and accurate
Not accurate and not precise
12
  • Percent error
  • Experimental (e) your value obtained
  • Accepted (a) the correct or true value
  • absolute value (make value positive)
  • Formula accepted experimental x 100
  • accepted
  • Shorthand a e x 100
  • a
  • Answer _____
  • (use correct of sig figs)

13
  • D. Types Of Measurements
  • SI units
  • SI - International System of Units (standard
    measurements in science)
  • Uses the metric system (based on 10)
  • Time seconds (s)
  • Temperature Kelvin (K)
  • Length meter (m)
  • Mass kilogram (kg)
  • Volume cubic meter (m3)

14
  • Prefixes used
  • Prefixes go in front of the unit symbol and are
    always lower case
  • Kilo (k) 1000 or 103 (1000 times larger)
  • Deci (d) 0.1 or 10-1 (10 times smaller)
  • Centi (c) 0.01 or 10-2 (100 times smaller)
  • Milli (m) 0.001 or 10-3 (1000 times smaller)

15
  • Length
  • Units
  • Meter (m) SI unit
  • Centimeter (cm)
  • Millimeter (mm)
  • Use a meter stick or ruler (cm side only)
  • Conversions
  • 1 m 100 cm 1000 mm
  • 1 cm 10 mm

16
  • Mass
  • Weight the force on an object by gravity
  • is different on the earth and moon
  • Mass the amount of matter (stuff) in an
    object
  • is the same with or without gravity
    (the same on the earth and moon)
  • Use a digital balance in lab

17
  • Mass (cont.)
  • Units
  • Kilogram (kg) SI unit
  • Gram (g)
  • Milligram (mg)
  • Conversions
  • 1 kg 1000 g
  • 1 g 1000 mg

18
  • Volume
  • Regular shaped solid
  • Measure using a meter stick or a cm ruler
  • V L x W x H
  • Units cm x cm x cm cm3
  • Irregular shaped solid
  • Measure using the displacement method (use
    graduated cylinder and water)
  • Units mL or L

19
  • Volume (cont.)
  • Liquid
  • Measure using a graduated cylinder at the
    meniscus (the bottom of the curve)
  • Units mL or L
  • Units
  • Liter (L)
  • Milliliter (mL)
  • Cubic centimeter (cm3) or (cc)
  • Conversions
  • 1 L 1000 mL
  • 1 mL 1 cm3 1 cc

20
  • Density
  • Density mass / volume
  • D m / V
  • Mass is in grams
  • Volume is either in cm3 or mL
  • Density of water (pure H2O) 1.0 g/mL
  • 1 g H2O 1 mL H2O
  • Object floats in H2O if D lt 1.0 g/mL
  • Object sinks in H2O if D gt 1.0 g/mL

21
  • Temperature
  • Scales
  • Fahrenheit (?F)
  • Celsius (?C)
  • Kelvin (K) SI unit
  • Only Celsius (used most of the time, especially
    in lab) and Kelvin are used!
  • Use a thermometer in lab
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