Density and Measurements in Chemistry
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Chapter 2: Measurement and Problem Solving
Calculate the density of a substance.
Use density as a conversion factor.
The density of a substance is the
ratio of its mass to its volume.
Measuring mass: use a balance
Measuring volume:
Formula (
l
x
w
x
h
) (
π
r
2
h)
Water displacement (V
f
-V
i
)
Units of density:
Solid substance = g/cm
3
Liquid substance = g/mL
A sample of liquid has a volume of
22.5 mL and a mass of 27.2 g.
D = m/V
m =
V =
For a liquid substance with a density of 1.32
g/cm
3
, what volume should be measured to
deliver a mass of 68.4 g?
A steel cylinder has a volume of 246 cm
3
and
a density of 7.93 g/cm
3
. What is its mass in
kilograms?
Density is an intensive property
It does not change, no matter the size of a
sample
▪
1 kg of gold has the same density as 1 g, or 1
lb, or 1000 kg, etc.
Every substance has a unique density
you can identify an unknown substance by
calculating its density and comparing it to
known values
Density changes with temperature
For most substances, an increase in
temperature results in a decrease in
density
▪
As temperature increases, molecules move
further apart. This increases the volume of the
substance while the mass remains the same –
thereby decreasing the density.
▪
So solids are more dense than liquids, which
are more dense than gases
The density of liquid water is 1.00 g/mL
Anything more dense than water will sink
Anything less dense than water will float
Water is one of a unique group of
substances that is actually less dense as
a solid than a liquid
Ice floats in water!
A jeweler offers to sell a ring to a woman and tells
her that it is made of platinum. Noting that the ring
feels a little light, the woman decides to perform a
test to determine the ring’s density. She places the
ring on a balance and finds that it has a mass of
5.84 g. She also finds that the ring displaces 0.556
cm
3
of water. Is the ring made of platinum? The
density of platinum is 21.4 g/cm
3
.
Mass = 5.84 g Volume = 0.556 cm
3
The woman takes the ring back to the jewelry
shop, where she is met with endless apologies. The
jeweler had accidentally made the ring out of silver
rather than platinum. The jeweler gives her a new
ring that she promises is platinum. This time when
the customer checks the density, she finds the
mass of the ring to be 9.67 g and its volume to be
0.452 cm
3
. Is this ring genuine?
Mass = 9.67 g Volume = 0.452 cm
3
Learn about the concept of density, how to calculate it using mass and volume, and practical measurements in chemistry. Discover the importance of units of density, solving for volume and mass, and identifying substances based on their density. Understand how density remains constant as an intensive property and how it can change with temperature. Enhance your problem-solving skills in chemistry through practical examples and formulas.
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Presentation Transcript
Calculate the density of a substance. Use density as a conversion factor.
The density of a substance is the ratio of its mass to its volume.
Measuring mass: use a balance Measuring volume: Formula (l x w x h) ( r2h) Water displacement (Vf-Vi)
Units of density: Solid substance = g/cm3 Liquid substance = g/mL
A sample of liquid has a volume of 22.5 mL and a mass of 27.2 g.
D = m/V m = V =
For a liquid substance with a density of 1.32 g/cm3, what volume should be measured to deliver a mass of 68.4 g?
A steel cylinder has a volume of 246 cm3and a density of 7.93 g/cm3. What is its mass in kilograms?
Density is an intensive property It does not change, no matter the size of a sample 1 kg of gold has the same density as 1 g, or 1 lb, or 1000 kg, etc.
Every substance has a unique density you can identify an unknown substance by calculating its density and comparing it to known values
Density changes with temperature For most substances, an increase in temperature results in a decrease in density
As temperature increases, molecules move further apart. This increases the volume of the substance while the mass remains the same thereby decreasing the density. So solids are more dense than liquids, which are more dense than gases
The density of liquid water is 1.00 g/mL Anything more dense than water will sink Anything less dense than water will float
Water is one of a unique group of substances that is actually less dense as a solid than a liquid Ice floats in water!
A jeweler offers to sell a ring to a woman and tells her that it is made of platinum. Noting that the ring feels a little light, the woman decides to perform a test to determine the ring s density. She places the ring on a balance and finds that it has a mass of 5.84 g. She also finds that the ring displaces 0.556 cm3of water. Is the ring made of platinum? The density of platinum is 21.4 g/cm3.
The woman takes the ring back to the jewelry shop, where she is met with endless apologies. The jeweler had accidentally made the ring out of silver rather than platinum. The jeweler gives her a new ring that she promises is platinum. This time when the customer checks the density, she finds the mass of the ring to be 9.67 g and its volume to be 0.452 cm3. Is this ring genuine?
