Ch. 1.4 & 1.6 Notes

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