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Ch. 1.4 & 1.6 Notes

Ch. 1.4 & 1.6 Notes. Units of Measurement, Dimensional Analysis. 1.4. Qualitative vs. Quantitative Qualitative – quality, subjective Quantitative – numerical, objective Quantitative – In Chemistry, we use combo of metric system/SI units ( Systeme International d’Unites …it’s French). 1.4.

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Ch. 1.4 & 1.6 Notes

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  1. Ch. 1.4 & 1.6 Notes Units of Measurement, Dimensional Analysis

  2. 1.4 • Qualitative vs. Quantitative • Qualitative – quality, subjective • Quantitative – numerical, objective • Quantitative – • In Chemistry, we use combo of metric system/SI units (Systeme International d’Unites…it’s French)

  3. 1.4 • Units • Common metric/SI units we use include: • Liters • Grams • Meters • Seconds • Kelvin • Moles

  4. 1.4 • Prefixes • We add prefixes to some of these units for larger/smaller quantities • Millimeters • Kilograms • Etc. • Table 1.5

  5. 1.4 • Why add prefixes? • 1 mm vs. 0.001 m • More efficient, appropriate for scale of measure • You don’t measure little things in meters, right?

  6. 1.4 • Temperature • Most places use ºC, U.S. uses ºF • 0ºC = freezing point of water • 100ºC = boiling point of water • Chemistry – work in ºC and K…forget all about ºF!

  7. 1.4 • Kelvin (K) is SI unit for temperature • Don’t say degrees Kelvin or ºK • Unit used most for temp. in chemistry • Most equations require temp. in K to get right answer! • 0 K is absolute zero  all motion stops, nothing colder

  8. 1.4 • K = ºC + 273.15 (must commit to memory!) • Practice! • 31.3 ºC  K • 50. K  ºC • 115 ºC  K • 393.15 K  ºC

  9. 1.4 • Answers • 304.5 K • 223 ºC • 388 K • 120.00 ºC • Did you remember sig figs? (Don’t worry, we’re going over that tomorrow!)

  10. 1.4 • Derived units • Combination of 2+ units • m/s (meters per second) • m/s (meters per second “squared”) • mol/L (moles per liter) • Etc.

  11. 1.4 • Volume • Typically use L (liters) • May see cm3 • What is this equivalent to? • Many tools for measuring volume in lab • Graduated cylinder, syringe, buret, pipet, volumetric flask/pipet

  12. 1.4 • Density = mass/volume • D = m/v • Units: usually g/mL or g/cm3 • Density of water = 1.00 g/mL • 25ºC (room temperature)

  13. 1.4 • Densities usually given at 25ºC • What happens to density if temperature… • Increases? • Decreases? • What’s an exception to this?

  14. 1.4 • Density ≠ weight • Density and water • What floats? • Sinks?

  15. 1.4 • Practice with density • Calculate the density of Hg if 1.00 x 102 g occupies a volume of 7.36 cm3. • Calculate the volume of 65.0 g of CH3OH if its density is 0.791 g/mL. • A piece of solid Au is 77.28 g and occupies a volume of 4.0 mL. What volume would a 30. g piece occupy?

  16. 1.4 • 13.6 g/cm3 • 82.2 mL • 1.6 mL

  17. 1.6 • Dimensional analysis • AKA making conversions given unit desired unit = desired unit given unit

  18. 1.6 A B = B A 500. mL .001 L = 0.500 L 1 ml

  19. 1.6 A B C = C A B 25 000 cm 1 km .01 m = 0.25000 km 1 cm 1000 m

  20. 1.6 • Dimensional analysis • Try using Mrs. B’s picket fence… at least for the last one! • 1.5 km  cm • 1000 mL  L • 13.7 m  μm (10-6) • 31 536 000 s  years

  21. 1.6 • 1.5 x 105 cm • 1 L • 13.7 x 10-6μm • 1.0000 year

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