homework tomorrow you will be doing your first “real” lab! (due to turnitin.com by sun. 9/30 at...

HOMEWORKTomorrow you will be doing your first “real” lab!

(Due to TurnItIn.com by Sun. 9/30 at 11:59 pm)Title: Density Blocks Lab

Purpose: Determine the density/identity of up to three and at least one type of unknown metal.

Materials: Metal shot, water, graduated cylinder, balance

You must write a complete pre-lab tonight (including an ORIGINAL PROCEDURE and blank data table) & bring it to class if you want to participate tomorrow

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

Comparing Densities (g/cm3)

Jaffe, New World of Chemistry, 1955, page 66

0.90.25

water 1.0

ice

cork

aluminum

2.7

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

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

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:

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

EEEE ==4

Significant figures: Rules for zeros

Leading zeros are not significant.

Captive zeros are significant.

Trailing zeros are significant.

Leading zeroLeading zero

Captive zeroCaptive zero

Trailing zeroTrailing zero

0.421

4012

114.20

– three significant figures

– four significant figures

– five significant figures

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 mL

10 mL

15 mL ?

15.0 mL

Practice Recording Temperature(Celcius)

0oC

20oC

40oC

60oC

80oC

100oC

EE0oC

10oC

20oC

30oC

40oC

50oC

60oC

AA 30.0oC

0oC

5oC

10oC

15oC

20oC

25oC

CC 19.0oC 60.oC

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


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

Counting Sig Figs

All digits are significant EXCEPT…

Leading zeros -- 0.0025

Trailing zeros without a decimal point -- 2,500


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


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 SF3 SF


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


homework tomorrow you will be doing your first “real” lab! (due to turnitin.com by sun. 9/30 at...

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