Transcript Diapositiva 1

Class Opener:
(a) A metal object has a mass of 8.4 g. The volume of
the sample is 3.1 mL. Calculate the density of the
object.
(b) Given the chart of densities below, determine the
composition of the object.
Substance
Density
Magnesium
1.75 g/mL
Aluminum
2.70 g/mL
Titanium
4.50 g/mL
Zinc
7.14 g/mL
Copper
8.96 g/mL
Density
• Common physical property used to identify
substances.
• Density – mass per unit volume of a substance.
D = m/V
• Mass – amount of matter that composes a substance
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Measured in units called grams.
Instrument used to measure mass – balance
Do not confuse mass with weight
Weight- measure of gravitational pull
on matter
• Mass does not depend on gravity.
Density Triangle
• Volume – amount of space occupied by a substance
– measured with instruments such as a graduated
cylinder or a pipet
– Commonly measured in units called milliters (mL).
– The volume occupied by 1mL is the same as 1 cubic
centimeter (cm3)
1mL = 1 cm3
– Another common unit of volume is the liter (L)
1 L = 1000 mL
Units of Volume
1. A bottle contains 87.5 mL of alcohol. Express
this volume in:
(a) cubic centimeter
(b) liters
Density
– Whether an object sinks or floats is dependent on
its density.
– Materials that are more dense sink in things that are
less dense.
– Every substance has its own unique density at a
particular temperature.
– Density varies with temperature. Density usually
decreases with increasing temperature.
Densities of Common Materials
Other Density Problems
Problem #1:
Copper has a density of 8.92 g/cm3. What is the
mass of a cube of copper that has a volume of
6.25 cm3?
Problem #2:
What is the volume of a sample of liquid mercury
that has a mass of 76.2 g? Given that the density
of mercury is 13.6 g/mL.
Phase Diagrams
One Minute Paper
• You have one minute to answer these two
questions concerning today’s lesson about
density.
– What was the most important thing you
learned?
– What is still muddy?