DENSITY
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DENSITY
Pb
Pb
Both of the above blocks consist of pure lead (Pb)
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Pb
Pb
WHICH BLOCK HAS THE GREATER DENSITY?
IF YOU ANSWERED, “THEY HAVE THE SAME DENSITY.”
YOU ARE CORRECT!!!
WHY?
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WHY?
1. Both of the above blocks consist of pure lead (Pb)
2. Density is a ratio of Mass to Volume (D=M/V).
Let’s do some calculations to explore this.
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Let’s take measurements of each block.
Small block:
mass: 272.16 g
Large Block:
mass: 1360.8 g
linear measurements:
linear measurements:
2.00cm x 3.00cm x 4.00cm
4.00cm x 5.00cm x 6.00cm
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Let’s calculate the volume of each block.
Small block:
mass: 272.16 g
Large Block:
mass: 1360.8 g
Volume Calculations:
Volume Calculationss:
2.00cm x 3.00cm x 4.00cm =
24.0 cm3
4.00cm x 5.00cm x 6.00cm =
120cm3
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Now let’s calculate the density of each.
Small block:
mass: 272.16 g
Volume: 24.0 cm3
Large Block:
mass: 1360.8 g
Volume: 120cm3
DENSITY=M/V
DENSITY=M/V
272.16 g = 11.3 g
24.0cm3
cm3
1360.8g = 11.3g
120cm3
cm3
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Small block:
mass: 272.16 g
Volume: 24 cm3
272.16g = 11.3 g =DENSITY
24.0cm3 cm3
Large Block:
mass: 1360.8 g
Volume: 120cm3
1360.8g = 11.3g = DENSITY
120cm3
cm3
Note: the mass to volume ratios (DENSITIES) are the same.
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Density as a Conversion Factor
Note: The units of density are in a
ratio form, so density can be used
as a conversion factor to change
mass to volume or volume to mass.
Let’s explore this.
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Problem: Determine the mass of a 1.00 L sample of Pb.
(The density of Pb is 11.3 g/cm3, 1 L = 1000mL =1000 cm3
Solution:
1. What are the units of what we are looking for?
__________________ =
g (mass units = grams)
2. What do we have?
1.00 L______________ =
g
3. Now convert L into g using density
1.00 L
1000 mL 11.3 g
1L
mL
=
11300 g
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Problem: Determine the volume of a 1.00 lb (454 g) sample
of Pb. (The density of Pb is 11.3 g/cm3)
Solution:
1. What are the units of what we are looking for?
__________________ =
cm3 (volume units)
2. What do we have?
1.00 lb______________ =
cm3
3. Now convert lb into cm3 using density
1.00 lb
454 g
1.00 lb
cm3
11.3 g
=
40.17
cm3
40.2 cm3
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Let’s compare the two solutions.
1.00 L 1000 mL 11.3 g
1L
mL
1.00 lb
454 g
1.00 lb
cm3
11.3 g
= 11300 g
= 40.17 cm3
Compare how density was used in the two solutions.
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Now work with someone next to you to solve this problem.
Problem: A rock having a mass of 136.17 g was placed in a
graduated cylinder containing water with an initial reading
of 23.0 mL. The water level rose to a reading of 48.5 mL.
Calculate the density of the rock.
Volume = 48.5 - 23.0 =25.5 mL
Density = 136.17 g = 5.34 g = 5.34 g
25.5 mL
mL
cm3
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Cooking oil has a density of approximately 0.952 g/mL.
a. Determine the mass of 550 mL of cooking oil.
550 mL
0 .9 5 2 g
mL
= 523.6 g
520 g
b. Determine the volume of 870 g of cooking oil.
870 g
mL
0 .9 5 2 g
= 913.9
910 mL
mL
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Densities of Some Common Materials
Substance
water (25oC)
ice (0oC)
Gold
Lead
sand
Density g/cm3
1.00
0.917
19.31
11.3
??
Does density change with temperature?
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