Ch. 1.4 & 1.6 Notes Units of Measurement, Dimensional Analysis
Jan 16, 2016
Ch. 1.4 & 1.6 NotesUnits of Measurement, Dimensional
Analysis
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
Units◦Common metric/SI units we use include:
Liters Grams Meters Seconds Kelvin Moles
1.4
Prefixes◦We add prefixes to some of these units for
larger/smaller quantities Millimeters Kilograms Etc. Table 1.5
1.4
Prefix Abbreviation
Meaning
Giga G 109
Mega M 106
Kilo k 103
Deci d 10-1
Centi c 10-2
Milli m 10-3
Micro µ 10-6
Nano n 10-9
Pico p 10-12
Femto f 10-15
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?
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!
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
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
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!)
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.
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
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)
1.4
Densities usually given at 25ºC◦What happens to density if temperature…
Increases? Decreases?
◦What’s an exception to this?
1.4
Density ≠ weight Density and water◦What floats?◦Sinks?
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?
1.4
13.6 g/cm3
82.2 mL
1.6 mL
1.4
Dimensional analysis◦AKA making conversions
1.6
given unit
given unit
desired unit = desired unit
1.6
A
A
B= B
500. mL
1 ml
.001 L= 0.500 L
1.6
A
A
B= C
25 000 cm
1000 m
1 km= 0.25000 km
C
B
.01 m
1 cm
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
1.6
1.5 x 105 cm 1 L 13.7 x 10-6 μm 1.0000 year
1.6