International System of Units

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International System of Units

• Units provide a scale on which to represent the
  results of a measurement

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Measurements of Length

• Length
• - Fundamental unit is the meter
• 1 meter 39.37 inches

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Measurements of Volume

• Volume
• - amount of 3-D space occupies by a substance
• - fundamental unit is meter3 (m3)
• 1 cm3 1 ml

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Items for measuring volume

• Graduated cylinder- useful for dispensing
  approximate volumes
• Buret- must be used when accuracy is important
• Volumetric flask- contains a specified volume of
  liquid

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Measuring Mass

• Weight- mass times gravity
• Mass- the amount of matter in an object
• - quantity of matter in an object
• - fundamental unit is the kilogram

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Measuring Density

• Density mass/ volume
• Derived unit- a unit obtained from more than one
  base unit.
• Density- is a characteristic property that
  depends only on the composition of a substance,
  not on the size of the sample.
• Pure substances have specific densities.
• The density of a substance generally decreases as
  its temperature increases. Water is an important
  exception

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Density Problems

1. What is the density of a block of marble that
   occupies 310cm3 and has a mass of 853g?
2. Diamond has a density of 3.26g/cm3. What is the
   mass of a diamond that has a volume of 0.350cm3?
3. What is the volume of a sample of liquid mercury
   that has a mass of 76.2g, given that the density
   of mercury is 13.6g/ml?

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Measuring Specific Gravity

• Specific Gravity- a comparison of the density of
  a reference substance. Water is a common
  reference substance.
• Can be determined with a hydrometer
• Specific Gravity density of substance/ density
  of water
• - Has no units

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Measuring Temperature

• Temperature- is related to the energy and motion
  of particles
• Temperature scales
• Celsius scale- based on the freezing and
  boiling points of water.
• a. freezing point 0 C
• b. boiling point 100 C

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• Kelvin scale- The zero point on the Kelvin scale
  is absolute zero. The theoretical point at which
  all motion stops. One degree Kelvin equals one
  degree celsius
• K C 273
• C K - 273

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Measuring Temperature

• Practice Problems
• Normal human body temperature is 37 C. What is
  your temperature in Kelvin?
• The boiling point of the element Argon is 87 K.
  What is the boiling point of argon in C?

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The Importance of measurement

• Scientific Notation

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Scientific notation

• 36,000 is 3.6 x 104
• The exponent indicates how many times the
  coefficient 3.6 must be multiplied by 10 to equal
  the number 36,000.
• Large numbers have positive exponents

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• Small numbers (less than one) have negative
  exponents.
• 0.0081 is 8.1 x 10-3, the exponent -3 indicates
  that the coefficient 8.1 must be divided by 10
  three times to equal 0.0081

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Multiplication and Division

• To multiply numbers written in scientific
  notation, multiply the coefficients and add the
  exponents
• (3.0 x 104) x (2.0 x 102) 6.0 x 106

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• To divide numbers written in scientific notation,
  first divide the coefficient, then subtract the
  exponent in the dominator from the exponent in
  the numerator
• 3.0 x 104 / 2.0 x 102 1.5 x 102

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Sample Problems

• Write each measurement in scientific notation
• 222 meters
• 2.22 x 102 meters
• 728500 meters
• 7.285 x 105 meters
• 0.00054 meters
• 5.4 x 10-4 meters

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• Multiplication and Division
• (3.0 x 105) x (2.6 x 103)
• 7.8 x 108
• (2.8 x 103) / (1.4 x 10-2)
• 2.0 x 105

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Conversion Factors

• Conversion factor- a ration of eqvivalent
  measurements, such as 100cm / 1m
• The measurement in the numerator is equivalent to
  the measurement in the denominator.
• Conversion factors are exact quantities.
  Therefore, they have an unlimited number of
  significant figures.