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Chemistry: An Introduction to General, Organic, and Biological Chemistry, Thirteenth Edition © 2018 Pearson Education, Inc.
Density
Learning Goal Calculate the density of a substance; use the
density to calculate the mass or volume of a substance.
Objects that sink in
water are more dense
than water; objects that
float are less dense.
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Chemistry: An Introduction to General, Organic, and Biological Chemistry, Thirteenth Edition © 2018 Pearson Education, Inc.
Density
Density
• compares the mass of an object to its volume.
• is the mass of a substance divided by its volume.
• is defined as
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Density
Substances that have
• higher densities contain particles that are closely packed together.
• lower densities contain particles that are farther apart.
• Metals such as gold and lead have higher densities because their
atoms are packed closely together.
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Density: Units
In the metric system, densities of solids, liquids, and gases are
expressed with different units.
• The density of a solid or liquid is usually given in grams per cubic
centimeter (g/cm3) or grams per milliliter (g/mL).
• The density of a gas is usually given in grams per liter (g/L).
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Densities of Common Substances
Insert table 2.9 page 46
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Chemistry Link to Health Bone Density
A condition of severe thinning of bone known as osteoporosis may
occur. Scanning electron micrographs (SEMs) show (a) normal
bone and (b) bone with osteoporosis due to loss of bone minerals.
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Chemistry Link to HealthBone Density
Bone density is often determined by passing low-dose X-rays
through the narrow part at the top of the femur (hip) and the spine (c).
Bones with high density will block more of the X-rays compared to
bones that are less dense.
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Density Using Volume Displacement
The density of the zinc object
is calculated from its mass
and volume.
mass of zinc 68.60 g 68.60 g Density of zinc 7.2 g/mL
volume of zinc 45.0 mL 35.5 mL 9.5 mL= = = =
−
4 SFs
2 SFs 2 SFs
A solid completely submerged in water displaces its own
volume of water (its volume is calculated from the volume
increase).
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Learning Check
What is the density (g/mL) of a 48.0-g sample of a metal if the level of water in a graduated cylinder rises from 25.0 mL to 33.0 mL after the metal is added?
object
33.0 mL25.0 mL
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Chemistry: An Introduction to General, Organic, and Biological Chemistry, Thirteenth Edition © 2018 Pearson Education, Inc.
Solution
What is the density (g/mL) of a 48.0-g sample of a metal if the level of water in a graduated cylinder rises from 25.0 mL to 33.0 mL after the metal is added?
Volume by displacement 33.0 mL 25.0 mL 8.0 mL
mass of sample 48.0 gDensity 6.0 g/mL
volume of sample 8.0 mL
= − =
= = =
3 SFs
2 SFs 2 SFs
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Chemistry: An Introduction to General, Organic, and Biological Chemistry, Thirteenth Edition © 2018 Pearson Education, Inc.
Problem Solving
Using Density
If the volume and the density of a sample are known, the mass in
grams of the sample can be calculated by using density as a
conversion factor.
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Problem Solving Using Density
Example: An unknown liquid has a density of 1.32 g/mL. What is
the volume (mL) of a 14.7-g sample of the liquid?
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Chemistry: An Introduction to General, Organic, and Biological Chemistry, Thirteenth Edition © 2018 Pearson Education, Inc.
Problem Solving Using Density
Example: An unknown liquid has a density of 1.32 g/mL. What is
the volume (mL) of a 14.7-g sample of the liquid?
STEP 1 State the given and needed quantities.
STEP 2 Write a plan to calculate the needed quantity.
grams millilitersDensity
Factor
ANALYZE Given Need Connect
THE PROBLEM 14.7 g milliliters density (g/mL)
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Chemistry: An Introduction to General, Organic, and Biological Chemistry, Thirteenth Edition © 2018 Pearson Education, Inc.
Problem Solving Using Density
Example: An unknown liquid has a density of 1.32 g/mL. What is
the volume (mL) of a 14.7-g sample of the liquid?
STEP 3 Write the equalities and their conversion factors
including density.
STEP 4 Set up the problem to calculate the needed
quantity.
1.32 g 1 mL1.32 g 1 mL and
1 mL 1.32 g=
1 mL14.7 g 11.1 mL of liquid
1.32 g =
3 SFs 3 SFs 3 SFs
Exact
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Learning Check
John took 2.0 teaspoons (tsp) of cough syrup for a cough. If the
syrup had a density of 1.20 g/mL and there is 5.0 mL in 1 tsp,
what was the mass, in grams, of the cough syrup?
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Solution
John took 2.0 teaspoons (tsp) of cough syrup for a cough. If the
syrup had a density of 1.20 g/mL and there is 5.0 mL in 1 tsp,
what was the mass, in grams, of the cough syrup?
STEP 1 State the given and needed quantities.
STEP 2 Write a plan to calculate the needed quantity.
teaspoons milliliters gramsU.S.−Metric
factor
Density
factor
ANALYZE Given Need Connect
THE PROBLEM 2.0 tsp grams conversion factors
of syrup (mL/tsp, density of syrup)
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Chemistry: An Introduction to General, Organic, and Biological Chemistry, Thirteenth Edition © 2018 Pearson Education, Inc.
Solution
John took 2.0 teaspoons (tsp) of cough syrup for a cough. If the
syrup had a density of 1.20 g/mL and there is 5.0 mL in 1 tsp,
what was the mass, in grams, of the cough syrup?
STEP 3 Write the equalities and their conversion factors
including density.
STEP 4 Set up the problem to calculate the needed
quantity.
1 tsp 5.0 mL 1 mL of syrup 1.20 g of syrup
5.0 mL 1 tsp 1.20 g syrup 1 mL syrup and and
1 tsp 5.0 mL 1 mL syrup 1.20 g syrup
= =
5.0 mL 1.20 g2.0 tsp 12 g of syrup
1 tsp 1 mL =
2 SFs Exact Exact 2 SFs
2 SFs 3 SFs
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Specific Gravity
• Specific gravity (sp gr) is a relationship between the density of a
substance and the density of water.
• Specific gravity is calculated by dividing the density of a sample
by the density of water, which is 1.00 g/mL at 4 °C.
• A substance with a specific gravity of 1.00 has the same density
as water (1.00 g/mL).
density of sample Specific gravity
density of water=
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Specific Gravity
A hydrometer is used to measure the
specific gravity of urine. The normal range
of specific gravity for urine is 1.003 to
1.030.
The specific gravity can decrease with type
2 diabetes and kidney disease. Increased
specific gravity may occur with
dehydration, kidney infection, and liver
disease.
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Specific Gravity
In a clinic or hospital, a
dipstick containing chemical
pads is used to evaluate
specific gravity.
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Concept Map