Chapter 3: Physical Properties

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Chapter 3 Physical Properties Forensic
Characterization of Soil
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Physical Evidence

• Physical properties color, odor, texture,
  hardness, phase (solid, liquid, gas), melting
  point, density, conductivity, refractive index,
  etc.
• Physical changes when two or more substance are
  combined (or separated) but, each substance
  retains its chemical identity (Example CuSO4
  water gives a solution)
• Physical changes changes in physical state
  (Example ice melting to water)

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Chemical Evidence

• Chemical properties inertness, reactivity,
  flammability, corrosiveness, oxidation,
  reduction, neutralization, etc.
• Chemical changes when matter reorganizes into
  different substances (Example CuSO4 NaOH).
• Indicators of chemical changes are a color
  change, formation of a solid (precipitate),
  formation of a gas, a spontaneous increase or
  decrease in temperature

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Chemical vs Physical Evidence?
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Physical Characteristics of Soils

• Soil a heterogeneous mixture of inorganic,
  organic and human-based materials
• Inorganic rock fragments and minerals
• Organic decayed remains of plants, bacteria,
  etc.
• Human miscellaneous materials of human origin

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Forensic Characteristics of Soils

• The value of soil as evidence rests with its
  prevalence at crime scenes and its
  transferability.
• Most soils can be differentiated by their gross
  appearance.
• A side-by-side visual comparison of the color and
  texture of soil specimens is easy to perform and
  provides a sensitive property for distinguishing
  soils that originate from different locations.
• Soil evidence must be carefully collected and
  compared to soil samples found at the scene.

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Collection of Soil Samples

• Take samples at crime scene, within a 100-yard
  radius, and from paths into and out of scene
• Soil found on the suspect, such as adhering to a
  shoe or garments, must not be removed.
• Take samples at alibi locations
• Need specimens only from the top surface
• Package in individual containers
• Preserve lumps of soil

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Forensic Analysis of Soils

• Examiners begin with a visual comparison of the
  color of the soils, using the Munsell soil color
  notation.
• Soils are passed through sieves to separate
  components by grain size.

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Gradient Tube Separation

• Some crime laboratories utilize density-gradient
  tubes to compare soils.
• These tubes are typically filled with layers of
  liquids that have different density values.
• When soil is added to the density-gradient tube,
  its particles will sink to the portion of the
  tube that has a density of equal value.

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Forensic Analysis of Soils

• In many forensic laboratories, forensic
  geologists will characterize the mineral content
  of soils.
• Forensic geologists encounter about 50 minerals
  on a routine basis.
• Minerals are identified visually using a
  microscope or powder x-ray diffraction.
• The combination of plant matter, minerals and
  human-made components in soil creates a unique
  signature that can be used to compare soil
  samples.

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Measurements
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Measurements

• Every measurement is a number followed by the
  measuring unit used.
• You are making a measurement when you check you
  weight , read your watch, take your temperature,
  etc.
• In science, the metric system is used.
• It is a decimal system based on a unit of 10.
• Prefixes increase or decrease the number by 10s.

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Basic Units in the Metric System

• length meter m
• time second s
• mass kilogram kg
• temperature Kelvin K
• amounts mole mol

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Other Units in the Metric System

• volume liter l
• energy joule j
• energy calorie cal
• temperature Celcius C

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US - Metric Conversions

• Length
• 1 inch 2.54 cm, 1 yard 0.914 m
• Mass
• 1 ounce 28.4 g, 1 pound 454 g
• Volume
• 1 ounce 29.6 mL, 1 quart 0.946 L
• Temperature
• C 5/9(F-32), F 9/5(C) 32

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Metric Prefixes

• Increase or decrease basic unit by 10
• Form new units larger or smaller than the basic
  units
• Indicate a numerical value
• prefix value
• 1 kilometer 1000 meters
• 1 kilogram 1000 grams

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Common Prefixes that Increase or Decrease a Unit
of Measure

• Prefix Symbol Value
• giga- G 1 000 000 000
• mega- M 1 000 000
• kilo- k 1 000
• deci- d 0.1
• centi- c 0.01
• milli- m 0.001
• micro- ? (mu) 0.000 001

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Learning Check

• Select the unit you would use to measure
• A. Your height
• 1) millimeters 2) meters 3) kilometers
• B. Your mass
• 1) milligrams 2) grams 3) kilograms

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Measurements

• Scientific Notation
• Measured and Exact Numbers

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Scientific Notation

• It uses a coefficient and a power of 10 to
  represent a decimal number.
• Example 0.000001 1x10-6, 1000 1x103
• Non-examples 1, 1/2, 100.5
• The power of ten indicates how many places the
  decimal point is moved
• Right negative left positive
• Scientific notation is activated on a calculator
  using a EE, EXP or SCI button.

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Learning Check

• A. Which is the correct representation of
  0.00964 in scientific notation?
• 1) 9.64x103 2) 9.64x10-3 3) 964x10-6
• B. Which is the correct representation of
  9.64x103 in decimal notation?
• 1) 9.64 2) 964 3) 9640

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Exact Numbers

• Integers obtained by counting
• 2 soccer balls
• 1 watch
• 4 pizzas
• Values obtained from equivalencies
• 1 liter 1000 milliliters
• 1 meter 100 cm
• Have no estimated digits exempt from SF rules

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Measured Numbers
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Measured Numbers

• Using a measuring tool to determine a quantity.
• Examples your height, weight or temperature.
• Measured numbers have variable accuracy and
  precision.
• Different levels of precision occur due to the
  number of calibration marks and the ability of
  user to estimate between them.

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Reading a Meterstick

• . l2. . . . I . . . . I3 . . . .I . . . . I4. .
  cm
• What is the length of the line?
• How your answer compare with your neighbors
  answer? Why or why not?

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Reading a Meterstick

• . l2. . . . I . . . . I3 . . . .I . . . . I4. .
  cm
• First digit (known) 2 2.?? cm
• Second digit (known) 0.8 2.8? cm
• Third digit (estimated) between 0.07- 0.09
• Length reported 2.87 cm
• or 2.88 cm
• or 2.89 cm

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Known Estimated Digits

• Known digits 2 and 8 are 100 certain
• The third digit 8 is estimated (uncertain)
• In the reported length, all three digits (2.78
  cm) are significant including the estimated one

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Measurements

• Accuracy and Precision

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Precision

• How well several measurements agree with each
  other.
• The precision of a measuring device and how it is
  used determines the number of significant
  figures.
• Example The density of Mg was measured to be
  1.685 g/mL, 1.69 g/mL, 1.67 g/mL, 1.7 g/mL.

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Accuracy

• Accuracy is how close a measurement is to the
  accepted or true value.
• Example the accepted density of Mg is 1.74 g/mL.
  The measured density is 1.73 g/mL.
• The level of accuracy expected is determined by
  the scenario hitting the edge of an archery
  target from 10 feet versus 1000 ft.

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Accuracy Precision
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Measurements

• Counting Significant Figures
• Significant Figures in Calculations
• Learning Rules

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Significant Figures (SF) in Measurements

• Significant figures in a measurement include the
  known digits plus one estimated digit.
• Determine the number of SF by counting the number
  of digits, left to right starting with the first
  non-zero digit.
• Number of Significant Figures
• 38.15 cm 4
• 5.6 ft 2
• 0.125 m __

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Counting SF with Zeros

• Number of Significant Figures
• 0.008 mm 1
• 0.0156 oz 3
• 0.0042 lb __
• 50.8 mm 3
• 2001 min 4
• 0.00405 m __
• 200 yr 1
• 48,600. gal 5
• 25,005,000 g __

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Significant Figures in Calculations

• A calculated answer must match the least precise
  measurement.
• Rounding to the correct significant figures is
  done differently for final answers from
• 1) adding or subtracting
• 2) multiplying or dividing
• You can apply the rules for SF at each major step
  in a calculation chain or only to the final
  answer.

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Adding and Subtracting

• The answer has the same number of decimal places
  as the measurement with the fewest decimal
  places.
• 9.2 one decimal place
• 1.34 two decimal places
• 10.54 round to 10.5 one decimal place

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Multiplying and Dividing

• Round (or add zeros) to the calculated answer
  until you have the same number of significant
  figures as the measurement with the fewest total
  significant figures.
• 1.34 (3 SF) / 25.20 (4 SF) 0.053174603
• round this off to 3 SF 0.0532
• 1.1 (2 SF) / 1.1 (2 SF) 1 1.0 (2 SF)

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Learning Check

• A. 235.05 19.6 2.1
• 1) 256.75 2) 256.8 3) 257
• B. 4.311 0.07
• 1) 61.58 2) 62 3) 60
• C. (2.54 X 0.0028)
• (0.0105 X 0.060)
• 1) 11.3 2) 11 3) 0.041

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Precise Measurements?
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Significant Figures (SF) Rules

• Determine the number of SF by counting the number
  of digits, left to right starting with the first
  non-zero digit.
• Leading zeros are not significant, embedded zeros
  are significant and a decimal point determines if
  trailing zeros are significant.
• Addition Subtraction The answer has the same
  number of decimal places as the measurement with
  the fewest decimal places.
• Multiplication Division Round (or add zeros)
  to the calculated answer until you have the same
  number of significant figures as the measurement
  with the fewest total significant figures.

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What are Rules?

• A rule is a generalization that summarizes
  chemical behavior.
• Examples scientific laws, chemical equations,
  math formulas, determination of significant
  figures, all nitrates are soluble, etc.
• Rules free you from learning many related facts
  but must be applied under specific circumstances.

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To Learn A Rule

• Learn its underlying facts and concepts.
• Try to restate it in your own words.
• Learn to identify when a rule is applied.
• Identify what the rule accomplishes.
• Identify exceptions to the rule.

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Other Strategies for Learning Rules

• Some rules can only be memorized.
• Link rules to concepts to create a frame of
  reference for applying the rule.
• Draw diagrams or flowcharts to summarize rules.
• Develop your own chemical rules when faced with
  tables or graphs.

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Testing Rules

• Questions which ask you to apply a rule are the
  most common.
• Short answer What is the number of significant
  figures in 0.632?
• Multiple choice The number of significant
  figures in 0.632 is a) 4 b) 3 c) 2 d)1
• Problems Applying Rules
• Questions that test exceptions Number of SF in
  0.00044?
• Choosing among related rules Answer in correct
  SF for (0.043 1.2345)/0.554?

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Measurements

• Conversion Factors and Problem Solving
• Density and Problem Solving

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Conversion Factors

• Equalities can be used to create conversion
  factors
• Example 1 m 100 cm
• Factors 1 m and 100 cm
• 100 cm 1 m
• We will use English-metric, metric-metric,
  measured number-exact number and percent
  conversion factors.
• Examples 100 cm/m, 10.0 mg/1 tablet, 20 0.20

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Solving Generic Problems Using Conversion Factors

• Identify or summarize all the numerical data
  including equalities and their unit labels
• Identify the answer and it units
• Develop a conversion plan to change one unit into
  another.
• Combine (usually multiply) the conversion factors
  so each unit NOT in the final answer cancels out.
• Calculate the final result with correct SF

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Solving Generic Problems Using Conversion Factors

• Example
• A physician ordered 1.0 g of tetracycline to be
  given every six hours to a patient. If your
  pharmacy has only 500. mg tablets in stock, how
  many tablets will you need for 1 dose?

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Density

• Which weighs more a kilogram of rocks or
  feathers?
• Which weighs more a liter of rocks or feathers?
• Will rocks or feathers float on water? Why?

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Learning Check

• Which diagram represents the liquid layers in
  the cylinder?
• (K) Karo syrup (1.4 g/mL), (V) vegetable oil
  (0.91 g/mL,) (W) water (1.0 g/mL)
• 1) 2) 3)

K
W
V
V
W
K
W
V
K
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Density
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Density

• Density compares the mass of an object to its
  volume
• Density mass g or g
  
• volume mL
  cm3
• Note 1 mL 1 cm3
• Specific gravity density of sample ( g/mL)
• density of water (1 g/mL)

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Solving Generic Problems Using the Mathematical
Formula Method

• Identify the math formula that includes the the
  given data and the unknown.
• Identify the unknown then assign numbers to each
  known quantity.
• Substitute the known values in the math equation.
• Algebraically transform the equation so that the
  unknown is alone on one side.
• Calculate the final answer, check the answers
  validity and the number of SF.

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Solving Generic Problems Using the Mathematical
Formula Method

• Example
• A thermometer contains 8.3 g of mercury. The
  density of mercury is 13.6 g/mL. What volume of
  mercury is in the thermometer?

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Volume by Displacement

• A solid displaces a matching volume of water
  when the solid is placed in water.

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Learning Check

• What is the density (g/cm3) of 48 g of a metal
  if the metal raises the level of water in a
  graduated cylinder from 25 mL to 33 mL?
• 1) 0.2 g/cm3 2) 6 g/cm3 3) 252
  g/cm3