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  Density Notes  

Density of Solids Lab             Density of Liquids Lab

 Density is defined as the mass of a unit volume of a substance. If, for example, you have 1.00 gram of water, it has a volume of 1.00 cm3. Its density is 1.00 g/cm3. The proper units would be kg/m3 but g/cm3 are frequently used. If 2.0 grams of sulfur has a volume of 1.0 cm3, the density of sulfur is 2.0 g/cm3. Expressed mathematically,     density = mass/volume

Solids - The table below which lists the densities of a variety of solids emphasizes that the densities of solids vary over a wide range. A few are less dense than water and thus will float. Others are ten to twenty times as dense as water. The density of ice is 0.92 g/cm3. When you place ice cubes in a glass of water they float. When they melt, why doesn't the water pour over the rim of the glass?

Liquids - First, with the exception of mercury, the range of densities of liquids is considerably narrower than that of solids. Liquids range from about 3/4's to twice the density of water.

Gases -  The table lists the densities of some common gases under similar conditions of temperature and pressure. Notice how different they are compared with solids and liquids. Density may allow us to determine the composition of certain pure substances. Usually other test will also be needed to distinguish between substances with similar densities.

  All density values in the following table are units of g/cm3

SOLIDS 

LIQUIDS

GASES
cork               0.24    gasoline           0.68 hydrogen          0.000 09
mahogany     0.85 octane              0.70 helium               0.00018
paraffin wax  0.9   grain alcohol    0.79 ammonia          0.000 77
ice                  0.92  wood alcohol   0.81 CO                    0.001 25
balsa wood   0.13       coconut oil       0.93 nitrogen            0.001 26
oak                 0.72 water, pure     1.00 air                     0.001 3
hard coal      1.4 - 1.8 water, sea       1.03 oxygen             0.001 43
sugar             1.6 glycerin           1.26 CO2                  0.00198
bone              1.6 chloroform      1.73  chlorine            0.003 21
concrete        2.3  mercury          13.6  
glass              2.4 - 2.8    
quartz             2.65    
flint                  2.6    
aluminum        2.7    
zinc                 7.1    
tin                    7.3    
iron                  7.9    
brass               8.5    
copper            8.9    
silver               10.5    
lead                 11.3    
gold                 19.3    
platinum          21.5    

 

 

Density Problems

1. In each case give an example of a common object that has:

        a.  low density and small volume

        b. low density and large volume

        c. high density and small volume

        d. high density and large volume

2.    a) name 2 solids that are less dense than water:

        b) name 2 liquids that are more dense than water:

        c) name 2 gases that are more dense than carbon dioxide:

3. One lead cube has an edge 1 cm long; a second lead cube has an edge 2 cm long:
        a) in what properties are the two cubes different?  Which of their properties are the same? Explain your answers.
        b) what is the mass of each cube?

 

4. Use the tables to answer the following: 

        a) you are given equal masses of lead, aluminum, platinum, and brass.  a)  Arrange these masses in order of increasing volume.

         b) you are given equal volumes of the same metals. Arrange them in order of increasing mass.

5. Under what conditions would it be difficult or impossible to measure the volume of a solid by displacement? Explain.

6. Use the tables to answer the following:

         a) what is the mass of 10.0 m3 of water

        b) what is the mass of 5 ft3 of aluminum

 

 7. Calculate the volume of 1 gram of each of the following: balsa wood, aluminum, alcohol, oxygen
 

8. Calculate the mass of: 10 mL of alcohol, 5 mL of platinum, 10 L of oxygen

 9. You are given a flat‑bottomed glass cylinder 3 ,cm wide and 25 cm high. How could you mark the cylinder along its length to measure volumes of 5, 10, 15 mL, and so forth to 100 mL?

Bonus Problems: Show the method you used to work the problem and the answer for bonus credit:

a) A 50. g bracelet is suspected of being gold-plated lead instead of pure gold. When it is dropped into a full

b) A room is 5 m long, 4 m wide, and 3 m high. What is the mass of the air it contains?

c) If gold cost $500/oz, how many mm on a side does a $10 000 cube of gold measure?

 d) One gram of gold can be beaten out into a foil 1 m2 in area. (Thus an ounce of gold can yield 300 ft2 of foil.) How many atoms thick is such a foil? The mass of a gold atom is 3.27E - 25 kg.


Added Notes:  Density and Archimedes

King Hieron of Sicily gave a jeweler gold to be formed into a crown. When the crown was delivered it weighed as much as the gold that had been given to the jeweler. The king thought foul play was afoot.

 Archimedes was asked to figure out if something had been substituted for part of the gold. When taking a bath Archimedes noted that the volume of his body was equal to the volume of water displaced when he sank into the tub. Also a submerged object lost as much weight as the weight of the water it displaced.

 He found the crown to occupy a volume greater than one would expect that much gold to occupy (by looking at the amount of water it displaced) and concluded that it contained some silver as well.

 

   Further notes: Buoyancy

  1. a heavy object floats if its volume is large enough to displace a volume of water of equal mass.

  2.  a rock held below the surface of water appears to lose weight due to buoyancy (buoyant force exist because water pressure increases with depth)

  3.  a diver under water suspended on a cable experiences forces on his body due to water pressure

  4. this diver experiences greater pressure against his feet (due to greater water pressure at greater depths) than on his head resulting in a net upward force (the buoyant force)

  5. if an object weighs less than the buoyant force, it floats

  6.  if it weighs more than the buoyant force, it sinks

  7. if its weight is equal to the buoyant force it can remain at any level

  8.  buoyant force is greater in denser liquids

  9. The buoyant force on an object is equal to the weight of the liquid it displaces.

  10.   a ship weighing 1E 4 kg displaces a great deal of water and will float  

  11. a cube of steel weighing 1E 4 kg will sink (its weight is the same but the cube doesn't displace nearly as much volume as the hull of the ship

 

SEE:   Why Is Water So Special!

 

Page Last Updated: Friday March 02, 2007           Webmaster: Larry Jones                 Pickens County School District