Density
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Transcript of Density
Density
The concentrationof matter in an object is known as density.
Computing Density
Density = mass (g) volume (cm3)
DETERMINE VOLUME:One way to determine volume is to use a
graduated cylinder to determine the displacement of water achieved by placing the object in a predetermined volume of water.
DETERMINE MASS:Use a triple beam balance to
determine the mass of the object.
RT = Pg. 1
Computing Density
DETERMINE VOLUME:Another way to determine
volume is to measure the height, length and width of a solid that is cubic or rectangular in design. The formula shown will determine the volume of the object.
Sample Density problem #1
A student determines the mass of a rock sample to be 156.3 g. The volume of the same rock sample is 51.3 cm3. What is the density of the rock sample?
Density = mass (g) volume (cm3)
Density = 156.3 g 51.3 cm3
Density = 3.0 g/cm3
Sample Density problem #2
Given the information provided, determine the density of the toy?
Mass of Toy Dinosaur = 10 g
Volume of Toy Dinosaur= ?
Density = mass (g) volume (cm3)
Density = 10 g = 12.5 g/cm3
0.8 cm3
Determining Relative Density
The densities of objects in gases and fluids can be determined by observing the “flotation” of the object in the fluid or gas
Density of helium gas = 0.2 g/cm3
Density of air= 1.2 g/cm3
Objects with lower densities than the fluid or gas they are in will float above objects with higher densities.
Liquid water has a density of 1.0 g/mL. Determine the relative densities of the objects in the glasses of water.
Determining Relative Density
The object has a relative
density less than water because it
floats.
The object has a relative
density more than water because it
sinks.
Physical Changes That Affect Density
If temperature of a gasincreases while pressure is constant…
-- molecules move faster-- molecules will move farther apart
(expansion)-- less mass per unit volume
DENSITY WILL DECREASE
Changes in temperature and pressure can change the densities of substances …. especially gases.
Example: Air that is heated is less dense
than air that is cooled.
Therefore, heated air will
rise above cooled air.
Physical Changes That Affect DensityChanges in temperature and pressure can change the densities of substances ….
especially gases.
If temperature of a gasdecreases while pressure is
constant…-- molecules move slower
-- molecules will move closer together (compression)
-- larger mass per unit volume
DENSITY WILL INCREASE
Example: Air that is cooled is more dense than air that is
heated. Therefore,
cooled air will sink below heated air.
Physical Changes That Affect DensityChanges in temperature and pressure can change the densities of substances ….
especially gases.
If the pressure on a gasincreases while the temperature
is constant…
-- molecules will move closer together (compression)
-- larger mass per unit volume
DENSITY WILL INCREASE
PressurePressure
Phases of Matter and DensityMatter on Earth exists in
three phases: solid, liquid, gas.
Most substances will increases in density as the substance changes phase from gas to liquid and from liquid to solid.
Water’s highest density exists in its liquid phase (3.98 C).
Liquid Iron = 7.2 g/cm3
Solid Iron = 7.8 g/cm3
Ice = 0.97 g/cm3Liquid Water
= 1.0 g/cm3
Density vs. Object Size and Shape
The density of an object will NOT change should an object change its size and/or shape.
Quartz crystal:Mass = 10.9 g
Quartz globe:Mass = 88..9 g
Density of quartz
2.6 g/cm3