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Density >

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Determining Density

Density

3.4


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Density > Determining Density

Density: mass of an object per unit volume.

3.4

~ Intensive property that depends only on the composition of a substance, not on the size of the sample.

Table T


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The density of corn oil is less than the density of corn syrup. For that reason, the oil floats on top of the syrup.

Density of water at room temp = 1.0 g/mL

Density of ice = .92g/mL

3.4


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Mass: measured on a balance, grams

Volume: solid – regular shape – l x w x h, cm3

irregular shape – water displacement

if m = 4 g, what is the density?

d = 4 g/ 2 mL = 2 g/mL

will it sink or float in water?

Volume: liquid – use graduated

cylinder

3.4

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SAMPLE PROBLEM

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3.11

Now, use dimensional analysis to solve for the volume!

3

3

10.5 14

1.3

md

Vg g

cm V

V cm


SAMPLE PROBLEM

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tin = Sn

Aug ’10

3

3

95.047.31 /

13.0

md

Vg

g cmV

V cm


SAMPLE PROBLEM

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June ’10 ans: (2) 2


SAMPLE PROBLEM

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SPECIFIC GRAVITY

~is the relationship of density to a standard

S.G. = density of a substance density of standard~has no unit

~density of standard for solids & liquids is water, =1g/mL

~density of standard for gases is air, d=1.29g/L

be careful!!!! memorize


SAMPLE PROBLEM

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Oxygen gas has a density of 0.001429 g/cm3. Determine its specific gravity.

Density of a gas must be in g/L to compare with air for SG.

Answer:

1.429 /

1.29 /

g LSG

g L

= 1.1107751938Final ans. (with SF): 1.108

3

3

0.001429 1 10001.429 /

1 1

g cm mLg L

cm mL L


SAMPLE PROBLEM

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Determine the mass of a bar that measures 12. cm x 20. cm x 1.0 cm. It has a specific gravity of 2.78.

Density of a solid must be in g/cm3 to compare with water for SG.

Answer: 3

2.781 /

densityofbar

g cm

3

3 3

2.78 /12. 20. 1.0

2.78 / 240 667.2

massdensityofbar g cm

cm x cm x cm

m g cm x cm g

Final ans. with SF: 670 g


SAMPLE PROBLEM

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3.10

EXTRA EASY PROBLEM

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