DO NOW…. HW = 1st formal prelab due tomorrow

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

Write out the three forms of the density equation. What are the most common units of density?

M = DV

D = M V

V = M D

DM

Vensity

ass

olume

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

The density of lead is 11,340 kg/m3. Find the density of lead in g/cm3

11,340 kg 1000 g 1 m 1 m 1 m = m3 1 kg 100 cm 100 cm 100 cm

11.34 g cm3

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

C19H28O2

A thimbleful of a neutron star would have a mass of over 90,718Mg. What is this mass in grams?

90,781 Mg 1 x 106 g =

1 Mg

9.0781 x 1010 g

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

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

Comparing Densities (g/cm3)

Jaffe, New World of Chemistry, 1955, page 66

0.90.25

water 1.0

ice

cork

aluminum

2.7

• 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

SI Prefixes(M) mega- 1,000,000

(k) kilo- 1,000

(d) deci- 1/10

(c) centi- 1/100

(m) milli- 1/1,000

(µ) micro- 1/1,000,000 Be sure to review how to use the example

column on your Prefix Reference Sheet!

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

62,000 mmCourtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

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.

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

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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