Chapter 1.3 Measuring with Scientific Units

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Chapter 1.3Measuring with Scientific Units
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Units of Measurement
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Types of Observations and Measurements

• We make QUALITATIVE observations of reactions
  changes in color and physical state.
• We also make QUANTITATIVE MEASUREMENTS, which
  involve numbers.
• Use SI units based on the metric system

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As a review
Another major cornerstone of science is called
the SI system, what is it?

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Metric System

• Based on multiples of ten.

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Memory Aid

• Kids
• Have
• Died
• By
• Doing
• Conversions
• Metrically

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SI Units

• Système International dUnités
• Uses a different base unit for each quantity

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Volume

• The amount of space an object occupies.
• The most commonly used metric units for volume
  are the _____ (L) and the milliliter (mL).
• A liter is a cube 1 dm long on each side.
• A milliliter is a cube 1 cm long on each side.

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SI Units

• Système International dUnités
• Uses a different base unit for each quantity

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Mass vs. Weight

• Mass Amount of Matter (grams, measured with a
  BALANCE)
• Weight Force exerted by the mass, only present
  with gravity (pounds, measured with a SCALE)

Can you hear me now?
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Density

• Physical property of a substance

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Density

• Can be used to identify a substance.
• Will an object more dense than a fluid float?
  Less dense? Why or Why not?

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Temperature

• A measure of the ____________ ____________
  ____________ of the particles in a sample.

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Temperature

• In scientific measurements, the Celsius and
  ____________ scales are most often used.
• The Celsius scale is based on the properties of
  water.
• 0?C is the freezing point of water.
• 100?C is the boiling point of water.

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Temperature

• The Kelvin is the SI unit of temperature.
• It is based on the ____________ of gases.
• There are no negative Kelvin temperatures.
• K ?C 273.15

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Temperature

• The Fahrenheit scale is not used in scientific
  measurements.
• ?F 1.8(?C) 32
• ?C (?F - 32)/1.8

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98.6F to C

• C (F 32)/1.8
• C (98.6 32)/1.8
• C (66.6)/1.8
• C 37

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37C to F

• F 1.8C 32
• F 1.837 32
• F 66.6 32
• F 98.6

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What is Scientific Notation?

• Scientific notation is a way of expressing really
  big numbers or really small numbers.
• It is most often used in scientific
  calculations where the analysis must be very
  precise.
• For very large and very small numbers, scientific
  notation is more concise.

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Scientific notation consists of two parts

• A number between 1 and 10
• A power of 10
• N x 10x
• Are the following in scientific notation?

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To change standard form to scientific notation

• Place the decimal point so that there is one
  non-zero digit to the left of the decimal point.
• Count the number of decimal places the decimal
  point has moved from the original number. This
  will be the exponent on the 10.
• If the original number was less than 1, then the
  exponent is negative. If the original number was
  greater than 1, then the exponent is positive.

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Examples

• Given 289,800,000
• Use 2.898 (moved 8 places)
• Answer 2.898 x 108
• Given 0.000567
• Use 5.67 (moved 4 places)
• Answer 5.67 x 10-4

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To change scientific notation to standard form

• Simply move the decimal point to the right for
  positive exponent 10.
• Move the decimal point to the left for negative
  exponent 10.
• (Use zeros to fill in places.)

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Example

• Given 5.093 x 106
• Answer 5,093,000 (moved 6 places to the right)
• Given 1.976 x 10-4
• Answer 0.0001976 (moved 4 places to the left)

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Learning Check

• Express these numbers in Scientific Notation
• 405789
• 0.003872
• 3000000000
• 2
• 0.478260

4.05789 X 105 3.872 X 10-3 3 X 109 2 X
100 4.78260 X 10-1
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Conversion Factors

• Fractions in which the numerator and denominator
  are EQUAL quantities expressed in different units
• Example 1 in. 2.54 cm
• Factors 1 in. and 2.54 cm
• 2.54 cm 1 in.

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How many minutes are in 2.5 hours?

• Conversion factor
• 2.5 hr x 60 min 150 min
• 1 hr
• cancel

By using dimensional analysis / factor-label
method, the UNITS ensure that you have the
conversion right side up, and the UNITS are
calculated as well as the numbers!
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Sample Problem

• You have 7.25 in your pocket in quarters. How
  many quarters do you have?
• 7.25 dollars 4 quarters
• 1 dollar

29 quarters
X
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Learning Check

• Write conversion factors that relate each of the
  following pairs of units
• 1. Liters and mL
• 2. Hours and minutes
• 3. Meters and kilometers

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Solution

• 1. quarts and mL 1 L 1000 mL
• 1 L and 1000 mL
• 1000 mL 1 L
• 2. hours and minutes 1 hr 60 min
• 1 hr and 60 min
• 60 min 1 hr
• 3. meters and kilometers 1 km 1000 m
• 1 km and 1000 m
• 1000 m 1 km

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Learning Check

• A rattlesnake is 2.44 m long. How long is the
  snake in cm?
• a) 2440 cm
• b) 244 cm
• c) 24.4 cm

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Solution

• A rattlesnake is 2.44 m long. How long is the
  snake in cm?
• b) 244 cm
• 2.44 m x 100 cm 244 cm
• 1 m

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Learning Check

• How many seconds are in 1.4 days?
• Unit plan days hr min
  seconds
• 1.4 days x 24 hr x ??
• 1 day

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Solution

• Unit plan days hr min
  seconds
• 1.4 day x 24 hr x 60 min x 60 sec
• 1 day 1 hr 1 min
• 1.2 x 105 sec

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Wait a minute!

• What is wrong with the following setup?
• 1.4 day x 1 day x 60 min x 60
  sec
• 24 hr 1 hr
  1 min

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English and Metric Conversions

• If you know ONE conversion for each type of
  measurement, you can convert anything!
• You must memorize and use these conversions
• Mass 454 grams 1 pound
• Length 2.54 cm 1 inch
• Volume 0.946 L 1 quart

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Learning Check

• An adult human has 4.65 L of blood. How many
  gallons of blood is that?
• Unit plan L qt
  gallon
• Equalities 1 quart 0.946 L
• 1 gallon 4 quarts
• Your Setup

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Solution

• Unit plan L qt gallon
• Setup
• 4.65 L x 1 qt x 1 gal
  1.23 gal
• 0.946 L 4 qt

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Uncertainty in Measurement
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Uncertainty in Measurements

• Different measuring devices have different uses
  and different ____________ of accuracy.

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Significant Figures

• The term ____________ figures refers to digits
  that were measured.
• When rounding calculated numbers, we pay
  attention to significant figures so we do not
  overstate the accuracy of our answers.

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Significant Figures

• All ____________ digits are always significant.
• All _________ zeros after a decimal point are
  significant.
• Zeroes ____________ two significant figures are
  always significant.
• Zeroes used solely ____________ are never
  significant.

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Significant Figures

• When addition or subtraction is performed,
  answers are rounded to the least significant
  place value (lowest accuracy).
• When multiplication or division is performed,
  answers are rounded to the number of digits that
  corresponds to the least number of significant
  figures in any of the numbers used in the
  calculation.

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Accuracy versus Precision

• ____________ refers to the proximity of a
  measurement to the true value of a quantity.
• ____________ refers to the proximity of several
  measurements to each other.