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**What weighs more, a pound of bricks**

DENSITY Here's an old joke: What weighs more, a pound of bricks or a pound of feathers? The answer is they both weigh the same. Which
takes up more space though? Obviously, the pound of feathers takes up way
more space (has a greater volume). This leads to a
very useful property of matter called DENSITY.

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**The bottom line is that density is not constant.**

DENSITY FACTS Most kinds of matter expand when
their temperatures rise and contract
when their temperatures drop. Thus, density changes with temperature. Very cold water is
denser than hot water because the
water molecules are closer together. So as temperature increases, density decreases. The bottom line is that density is not constant. At 4°C pure water has a density of about 1 g/cu.cm, 1 g/ml. What is the density of ice?

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Demonstrations: Water and ice: What can you infer
about the density of these items?

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**Gases are always less dense than liquids and solids. **

That’s why air bubbles in a glass of water
move upward and escape. The solid states of matter generally
have higher densities than do the
liquids. One very important exception to this rule
is ordinary water. Water expands when
it freezes. The H2O molecules arrange
themselves in a pattern that takes up
more space than when the molecules
are in the liquid state. Therefore, ice floats in water.

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**Dead Sea Demonstrations:**

Water and oil: What can you infer
about the density of these items? Soda vs. Diet Soda: What can you
infer about the density of these items? Demonstrations: Dead Sea

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**Life jackets make us less dense than water, so we float.**

Substances that have a density less than
water's will float in water. Substances with a
greater density than water's will sink. Life jackets make us less
dense than water, so we float. Submarines can change
depth in the water when
they remove or add water
to special tanks called
ballast tanks. When water
is removed from the tanks,
the submarine loses mass.
It floats higher in the
water. When water is
added to the tanks, the
submarine gains mass. It
sinks lower in the water
because its density is now
greater.

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**What is the density of a rock that has a mass of 25**

What is the density of a rock that has a mass of 25.2 g
and a volume of 11.9 mL? Use the 3-step method to solve this problem: 1) Write the formula. D = M/V 2) Plug in the numbers and units. D = 25.2g / 11.9 mL 3) Complete the calculation and show the correct unit for density. D = 2.1 g/mL

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**D stands for density, M stands for mass, and V stands for volume.**

Density is a measure of how closely the
particles of a substance are packed into a
given space. Density is found by measuring mass and
volume and then dividing the mass by the
volume. The formula for density is: D = M/V D stands for density, M stands for mass,
and V stands for volume.

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**What is the density of a rock that has a mass of 32**

What is the density of a rock that has a mass of
32.5 g and a volume of 12.8 mL? Use the 3-step method to solve this problem: 1) Write the formula. D = M/V 2) Plug in the numbers and units. 3) Complete the calculation and show the correct unit for density.

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**What is the density of a rock that has a mass of 32**

What is the density of a rock that has a mass of
32.5 g and a volume of 12.8 mL?

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**You have a rock with a volume of 15cm3 and a mass of 45 g**

You have a rock with a volume of 15cm3 and a mass of 45 g. What is its density? Click for
answer You have a different rock with a volume of 30cm3 and a mass of 60g. What is its density? Click for
answer What is the density of a board whose dimensions are
5.54 cm x 10.6 cm x 199 cm and whose mass is 28.6 Kg? Show your answer in grams/cubic centimeters. Click for
answer

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**You have a rock with a volume of 15cm3 and a mass of 45 g**

You have a rock with a volume of 15cm3 and a mass of 45 g. What is its density? Back to
Problems

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**You have a different rock with a volume of 30cm3 and a mass of 60g**

You have a different rock with a volume of 30cm3 and a mass of 60g. What is its density? Back to
Problems

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**What is the density of a board whose dimensions are 5. 54 cm x 10**

What is the density of a board whose dimensions are
5.54 cm x 10.6 cm x 199 cm and whose mass is 28.6 Kg? D = M/V 5.54 cm x 10.6 cm x 199 cm = cm3 cm3 28.6 Kg D= kg/cm3

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D= kg/cm3 k h da g d c m D = 2.45 g /cm3 Back to
Problems

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Substance Density (g/cm3) Platinum 21.4 Seawater 1.025 Gold 19.3 Water 1.00 Mercury 13.6 Ice 0.92 Lead 11.3 Oil 0.90 Silver 10.5 Paraffin (wax) 0.87 Copper 8.9 Gasoline 0.7 Brass 8.5 Wood (oak) Iron 7.9 Wood (pine) 0.4 Steel 7.8 Cork 0.24 Aluminum 2.7 Oxygen 0.0014 Marble 2.69 Air 0.0013 Rubber 1.1 Helium 0.0002

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**Work these problems in your notebook.....**

1. A man is buying a copper bowl because he heard it is the best material to whip egg whites in. If the bowl has a mass of 142 g and a volume of mL, is it a real copper bowl?. 2. What volume would a gram sample of air occupy if the density of air is 1.29g/L? 3. Explain the beaker in the front of the room in terms of density.

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1. A man is buying a copper bowl because he heard it is the best material to whip egg whites in. If the bowl has a mass of 142 g and a volume of mL, is it a real copper bowl? D= 142g / mL D= 8.9 g/mL Is it copper? YES! 2. What volume would a gram sample of air occupy if the density of air is 1.29g/L? D= M/V 1.29 g/L = g/ V make it simple 12=36/3 1.29 g/L = 0.451g/ .349 L

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**3. Explain the beaker in the front of the room in terms of density.**

The yellow liquid at the top of the beaker is less dense than the other substances. The bluish substance is more dense than the top substance, but less dense than the bottom substance. The red bottom substance is the most dense.

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**Together, we can feed the world. **

Essays must be between 700 to 1,000 words in length, include a list of research sources, and fall under one of these four categories: Together, we can feed the world. Together, we can build a secure energy future. Together, we can protect people and the environment. Together, we can be innovative anywhere. Dupont Science Essay Challenge

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**Write the following in each line, from most dense to least dense....**

water, oil, ice gasoline, mercury, iron air, oxygen, helium sea water, ice, water

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water, ice, oil mercury, iron , gasoline
oxygen, air, helium seawater, water, ice

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Acrylic-clear Aluminum- shiny silver Brass- gold colored Copper- copper, reddish Oak-darker wood Pine-lighter wood Polypropylene-cloudy PVC-dark gray Steel-lighter gray, metallic, heavy

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**D=M/V Acrylic Substance H Density (g/cm3) Sink or Float? Aluminum**

Mass
(g) L (cm) W H Volume
(cm3) Density
(g/cm3) Sink or
Float? Acrylic Aluminum Brass Copper Oak Pine Polypropylene PVC Steel D=M/V WRITE EQUATIONS IN MARGIN

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**Acrylic Substance W (cm) H (cm) Volume (cm3) Density (g/cm3)**

Mass (g) L (cm) W (cm) H (cm) Volume
(cm3) Density (g/cm3) Sink or
Float? Acrylic 18 g 2.5cm 15.6 cm3 g/cm3 S Aluminum 43 g 2.7 g/cm3 Brass 134 g g/cm3 Copper 144.3 g 8.94 g/cm3 Oak 11.0 g g/cm3 F Pine 7.5 g g/cm3 Polypropylene 15 g g/cm3 PVC 22.2 g g/cm3 Steel 126.2 g 7.9 g/cm3

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Density Lab INTRO: Understanding the concept of density is very important in the world of science as well is in our
everyday lives. Scientists use density calculations to help
analyze how “tightly packed” a material’s particles are.
They also use this calculation to be able to identify
various materials due to the fact that each substance has
a unique density. In our lives, we use the concept of
density to understand the relationship between different
types of materials. We use terms such as hardness or
heaviness to describe the density of various items in our
daily language. PURPOSE: The purpose of this lab is for you to practice gathering mass and volume measurements as well as to use
your collected data to make density calculations.

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PROCEDURE: Eight items are listed in the table on the data sheet for this lab. Record the mass, volume, method for finding volume,
and density in the table. MASS - To measure mass, use a triple-beam balance. Be sure
to round your measurement values to the nearest tenth of a
gram (one decimal place) and to include a label after the number. VOLUME - To measure volume, choose one of the various
options available (listed below) and be sure to include a label with
your final answer (either mL or cm3). reading a graduated cylinder multiplying length x width x height water displacement (using a graduated cylinder and/or a spill can) DENSITY - Calculate density using the three-step method
discussed in class. Round your answer to the tenth. Be sure to
label your answer appropriately. Compare your answer to the correct answer posted at the
front of the room. If your answer is not close to this, you will
need to re-do your measurements and calculate the density again
to get closer to the correct answer.

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Substance Mass(g) Volume
(cm3 or mL) How you
found
volume Density (g/ml or
g/cm3(three-step
method) Glycerine Methyl
Alcohol Wood Rubber
Stopper Wax Rock
(Granite) Mineral Oil Water

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**APPLYING WHAT WE HAVE LEARNED**

Would gasoline float OR sink if mixed with water? _______________ Would an ice cube float OR sink if dropped in oil? _______________ Does helium gas float OR sink in air? _______________ Mercury is a liquid at room temperature. Would an iron bolt float OR sink in mercury? _______________ Write the formula for density: ________________________________________ What equipment is used to measure an item’s volume? ______________________ What label(s) do we commonly use to represent volume? ____________________ What equipment is used to measure a substance’s mass? _____________________ What label do we commonly use to represent mass? _______________ Is it easier to measure the volume of a liquid or a solid? Explain your answer.
__________________________________________________________________ __________________________________________________________________ Do you feel that this lab has helped you develop a better understanding of the concept of density? Explain.

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Density Worksheet Density is the ratio of the mass of the substance to the volume of the substance at a given temperature. Density has units of g/ cm3 or g/cc or g/mL for liquids and solids, and g/L for gases. SHOW YOUR WORK! 1. A gold-colored ring has a mass of 18.9 grams and a volume of 1.12 mL. Is the ring pure gold? (The density of gold is 19.3 g/mL.) 2. What volume would a gram sample of air occupy if the density of air is 1.29 g/L? 1.29g/L = 0.871g / V (4= 12/3) .871g/1.29g/L= .675 L D=18.9g / 1.12 mL D= g/mL

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**D= . 95 Yes, pumice will float in water!**

3. Pumice is volcanic rock that contains many trapped air bubbles. A 225 gram sample occupied mL. What is the density of pumice? Will pumice float on water? D = 225g/236.6mL D= Yes, pumice will float in water! 4. A cup of sugar has a volume of 237 mL. What is the mass of the cup of sugar if the density is 1.59 g/mL? 1.59g/mL = m / 237 mL 9 = 27/3 1.59 x 237 = m = g

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5. From their density values, decide whether each of the following substances will sink or float when placed in sea water, which has a density of g/mL. Float Gasoline 0.66 g/m Sink Mercury 10.6 g/mL Float Cork 0.26 g/mL 6. A sample of lead is found to have a mass of 32.6 g. A graduated cylinder contains 2.8 mL of water. After the lead sample is added to the cylinder the water level reads 5.7 mL. Calculate the density of the lead sample. 5.7 mL -2.8 mL 2.9 mL D= 32.6 g / 2.9 mL D=11.24 g/mL

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**Mass to Volume must be greater than 1 g/mL 450cm3 = 450 mL **

7. A little aluminum boat (mass of g) has a volume of cm3. The boat is place in a small pool of water and carefully filled with pennies. If each penny has a mass of 2.50 g, how many pennies can be added to the boat before it sinks? Mass to Volume must be greater than 1 g/mL 450cm3 = 450 mL needs to be greater than 450 g to sink 450 g g of boat = g 435.5 g/ 2.5 g (penny) 174.2 pennies to equal density 175 pennies to sink da boat!

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**8. Density varies with change in temperature. Why?**

If the temperature changes, then the particles move further apart, cause thermal expansion to occur, which would make a higher volume, which would cause a change in density.

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9. The King of Artemesia was given a gift of a crown of gold, but he suspected that he was being fooled. He asked his court scientist (that’s you) to prove if the crown was really gold or not. You found the mass of the crown was g. The volume of the crown was 53.2 ml. Is the crown made of gold? Include as much detail as you possibly can to prove your point. Use your Density Reading for help. If the crown is not made of gold, what material is it made of? How do you know? D= g / 53.2 mL D = 8.50 g/mL The crown can not be gold, as the density of gold is 19.3 g/mL. With a density of 8.5 g/mL, the crown must be made out of brass. Brass looks like gold, but is not gold at all! Brass is made up of an alloy of zinc and copper.

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Mrs. O’Rourke September, 2006

Mrs. O’Rourke September, 2006

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