DO NOW….Which liquid has the highest density?

52

3

1

4

Coussement, DeSchepper, et al. , Brain Strains Power Puzzles 2002, page 16

least dense 1 < 3 < 5 < 2 < 4 most dense

• Density is an INTENSIVEINTENSIVE propertyproperty of matter.

- does NOT depend on quantity of matter.

-Examples: color, melting point, boiling point, odor, density

• DIFFERENT THAN EXTENSIVE propertiesEXTENSIVE properties

- depends on quantity of matter.- mass, volume, length

Styrofoam Brick Gold

Density

M = DV

D = M V

V = M DD

M

Vensity

ass

olume

The heaviest human brain ever recorded had a mass of 2.3kg. How many micrograms is that?

2.3 kg 1000 g 1 x 106 µg =

1 kg 1 g

2.3 x 109 µg

The density of lead is 11.34 g/cm3. Find the density of lead in kg/m3

11.34 g 1 kg 100 cm 100 cm 100 cm = cm3 1000 g 1 m 1m 1m

11,340 kg m3

The average concentration of testosterone in the blood of a male in his twenties is 550 nanograms per deciliter. How many grams per cubic centimeter does this concentration represent?

550 ng 1 g 10 dL 1 L 1 mL = dL 1 x 10 9 ng 1 L 1000 mL 1 cm3

5.5 x 10-9 g cm3

Density of Some Common Substances

Density of Some Common Substance

Substance Density (g / cm3)

Air 0.0013* Lithium 0.53 Ice 0.917 Water 1.00 Aluminum 2.70 Iron 7.86 Lead 11.4 Gold 19.3

Density of Some Common Substance

Substance Density (g / cm3)

Air 0.0013* Lithium 0.53 Ice 0.917 Water 1.00 Aluminum 2.70 Iron 7.86 Lead 11.4 Gold 19.3

*at 0oC and 1 atm pressure

Consider Equal MassesEqual masses……but unequal volumes.

The object with the larger volume (aluminum cube) has the density.

aluminum

gold

Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 71

smaller

Christopherson Scales

Made in Normal, Illinois USA

Comparing Densities (g/cm3)

Jaffe, New World of Chemistry, 1955, page 66

0.90.25

water 1.0

ice

cork

aluminum

2.7

Density Practice Problems

1. What is the density of carbon dioxide gas if 0.196 g occupies a volume of 100. mL?

0.196 g

100. mL 1.96 x 10-3 g/mL

D = M V

Density Practice Problems2. An irregularly shaped stone has a

volume of 5.0 mL. The density of the stone is 1.75 g/mL. What is the mass of this stone?

1.75 g/mL x 5.0 mL 8.8 g

M = D x V

Density Practice Problems

3. A sample of iron has a mass of 94 g and a density of 7.8 g/cm3. What is the volume of the iron?

94 g

7.8 g/cm3 12 cm3

V = M D

SI Prefixesmega- 1,000,000

kilo- 1,000

deci- 1/10

centi- 1/100

milli- 1/1,000

micro- 1/1,000,000

Also know…

1 mL = 1 cm3

Practice Measuring

4.5 cm

4.54 cm

3.0 cm

Timberlake, Chemistry 7th Edition, page 7

cm0 1 2 3 4 5

cm0 1 2 3 4 5

cm0 1 2 3 4 5

20

10

15 mL ?

15.0 mL

Scientific Notation

Calculating with scientific notation (5.44 × 107 g) = ??

(8.1 × 104 mol)

5.44 EEEE ÷÷7 8.1

= 671.6049383 = 670 g/mol = 6.7 × 102 g/mol

Type on your calculator:

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EEEE ==4

Scientific Notation

Converting into scientific notation:

Move decimal until there’s 1 digit to its left. Places moved = exponent.

Large # (>1) positive exponentSmall # (<1) negative exponent

Only include sig. figs.

65,000 kg 6.5 × 104 kg

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Scientific Notation

2,400,000 g

0.00256 kg

7 10-5 km

6.2 104 mm

Practice Problems

2.4 106 g

2.56 10-3 kg

0.00007 km

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Significant figures: Rules for zeros

Leading zeros are not significant.

Captive zeros are significant.

Trailing zeros are significant, only IF there is a decimal point somewhere in the number.

Leading zeroLeading zero

Captive zeroCaptive zero

Trailing zeroTrailing zero

0.421

4012

114.20

– three significant figures

– four significant figures

– five significant figures

11,420 – four significant figures

Other Ways of Thinking About Significant Figures…

All digits are significant EXCEPT…

Leading zeros -- 0.0025

Trailing zeros without a decimal point -- 2,500

Pacific Ocean = “Present” and Atlantic Ocean = “Absent”

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Significant Figures

Calculating with Sig Figs (con’t)

Exact Numbers do not limit the # of sig figs in the answer.Counting numbers: 12 studentsExact conversions: 1 m = 100 cm

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Significant Figures

Calculating with Sig Figs

Multiply/Divide - The # with the fewest sig figs determines the # of sig figs in the answer.

(13.91g/cm3)(23.3cm3) = 324.103g

324 g

4 SF 3 SF 3 SF

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Significant Figures

Calculating with Sig Figs

Add/Subtract - The # with the fewest places after the decimal point determines the # of sig figs in the answer.

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18.9 g

- 0.84 g

18.1 g18.06 g

Significant Figures

(15.30 g) ÷ (6.4 mL)

Practice Problems

= 2.390625 g/mL

18.1 g

18.9 g

- 0.84 g18.06 g

4 SF 2 SF

2.4 g/mL2 SF

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