Density
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Transcript of Density
![Page 1: Density](https://reader036.fdocuments.in/reader036/viewer/2022062517/568130b9550346895d96db43/html5/thumbnails/1.jpg)
Density
• Is a physical property of matter• Every pure substance has its own
density• Is important for the identification of a
sample of matter• Is an intensive property of matter
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Density• Density is defined as mass per unit
volume.
• The relationship can be written mathematically as:
densit y = mass
volumeOR
d = mv
units: solids [ g / cm3 ] liquids[ g / mL] gases[ g / L]
![Page 3: Density](https://reader036.fdocuments.in/reader036/viewer/2022062517/568130b9550346895d96db43/html5/thumbnails/3.jpg)
Comparison of Densities
Each cube represents a volume of 1.00 cm3. The mass of each sample increases while the volume remains constant.
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Example:
• The sample of matter you have has a mass of 3.51 g and occupies a volume of 1.30 cm3.
d =mv
=3 .5 1 g
1 .3 0 cm2 .7 0 g / cm3
3
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v =md
4 5 .0 g0 .7 8 9 g / m L
5 7 .0 3 4 m L
EXAMPLE:
You need to add 45.0 g of alcohol to a sample. It is difficult to weigh an exact mass of a liquid. It is much easier to measure an exact volume. Using the density of the alcohol (0.789 g/cm3), you can determine what volume you would need to add to your sample so that you would be adding only the 45.0 grams.
= 57.0 mL in the correct number of sig figs
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Determining the Volume
• In order to figure the density we need to determine the volume:
• For regularly shaped objects we use direct measurement:
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Measuring Volume by Displacement
• Used for irregular shaped objects • Select a graduated cylinder large enough
to put the object in• Add water and accurately record the initial
volume.
![Page 8: Density](https://reader036.fdocuments.in/reader036/viewer/2022062517/568130b9550346895d96db43/html5/thumbnails/8.jpg)
• SLOWLY add the object to be measured:
rubber stopper
rock
metal cylinder• Read the new level of the
water• The water will rise an
amount equal to the volume of the object
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What not to do
![Page 10: Density](https://reader036.fdocuments.in/reader036/viewer/2022062517/568130b9550346895d96db43/html5/thumbnails/10.jpg)
Here’s what the cylinder should look like
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Do the math
1 . Original reading of volume
2. Final volume of water
3. This will equal the volume of the object
• 22.5 mL - 17.4 mL = 5.1 mL• Therefore, the volume of the object by
displacement is 5.1 mL
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Final volume 24.35 mLInitial volume - 20.45 mL
= volume of solid 3.90 mL
EXAMPLE:An irregularly shaped piece of quartz was place in a graduated cylinder containing 20.45 mL of water. The volume of the ater rose to 24.35 mL. What is the volume of the water?
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Classroom Exercises:
Blue Block• Mass = 79.4 grams • Volume=29.8 cubic cm.
• D = 79.4 g ÷ 29.8 cm3 = 2.66443
= 2.66 g/ cm3
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Green Block• Mass= 25.4 grams • Volume=29.8 cubic cm
• D = 25.4 g ÷ 29.8 cm3 = .85235
= .852 g/ cm3
Which block is more dense?
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Cylinder
• Radius = 3.5cm• Length = 7.25 cm• Mass = 32.3 g• What is the volume?
V = π X radius2 X heightπ = 3.14
What is the density?
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Sphere• Diameter = 7.0cm• Radius = 3.5cm• Mass = 32.3 g• What is the volume?
V = 4/3 π X radius3
π = 3.14
What is the density?
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Density
• Can also be used as a means of separating components of matter
• Ex: if 2 solids of a different density are mixed together, the solid with the greater density will gravitate to the bottom
• When a solid object is placed in a liquid that has a great density, the solid object will float.
• We will test this hypothesis in lab.
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Density Gradient
![Page 19: Density](https://reader036.fdocuments.in/reader036/viewer/2022062517/568130b9550346895d96db43/html5/thumbnails/19.jpg)
THE DENSITY CONCEPT
• The picture illustrates a density gradient.
• Each item (solid or liquid) is arranged in the cylinder according to its density.
• The samples are arranged with the greater densities toward the bottom and the lowest density on the top.
The Concept of Density for Liquids and Solids
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Which kind of matter is more dense?
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Question for you- Why does ice float?
• Solid H2O (ice) is less dense than liquid H2O (water).
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• Rivers never become completely frozen because as soon as water freezes, it floats up to the surface.
• Fish live in the unfrozen, denser liquid water below the layer of ice.
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• Comparison of:
Liquid water Ice
Mass = 100 g Mass = 100 g
Volume = 100 mL Volume = 110 mL
Density = 1.0 g/mL Density = 0.92 g/mL