Density - PowerPoint by zhangyun


Thur 8/30/07
Terminology: Mass vs Weight
• We may use the two terms interchangeably, but
    they do refer to different things.
•   What is the difference?
•   Mass = the amount of matter in a substance
•   Weight = the amount of gravity pulling on the
    object’s matter
•   Weight can change depending on location, mass
    can not.
•Your weight on the
moon is less than it
would be on Earth
since you are at a
further distance
from Earth. There
is less pull from the
Earth on you.
•Because the moon
has 1/6th the gravity
of Earth, you would
weigh six times
less than what you
weigh on Earth.

• The amount of space an object takes up.
Methods for determining volume
• Measurement (length x width x height)
  – Regular object
• Graduated Cylinder
• Water Displacement
  – Irregular object
Metric Volume and Length

 Insert figure 3.5
Units of mass and volume

• Mass is most often expressed in units of
• Volume is most often expressed in units of
  ml or cm3.
              Mass vs. Volume Graph for some substance

           Mass (g)          D= m/V where slope is equal
                           to density of substance

                      Volume (mL)

• What is density?
     Density is the amount of mass in a given
       amount of space
•   A pound of feathers vs a pound of lead. It
    takes more feathers to equal a pound. Why?
•   Lead has a higher density (more matter
    [mass] packed into a certain space) than
Q: A 5 kg mass displaces water from
13mL to 156mL. What is the density?
D= M
   To get volume: 156mL - 13mL =143mL

        To get mass: 5kg x 1000g = 5000g

                                           D       V
 D = 5000g / 143mL = 30 g/mL
Density Sample problem 2

• 2. A 58.85mL substance is found to have
 a mass of 46.2g. Using the table below,
 identify the substance.
 Substance           Density (g/cm3)   Solution:
 Diethyl ether       0.714             D= 46.2g/ 58.85mL
 Isopropyl alcohol   0.785             =0.785g/mL = 0.785 g/cm3
 toluene             0.867
More Density practice
• 3. A detective uncovers a bottle of what he thinks is
  chloroform at the scene of a crime. He determines the
  substance has a volume of 10.3mL. If the density of
  chloroform is 1.483g/cm3, what must the mass be in
  order for his suspicions to be correct?
           (1.483 g/cm3 x 10.3 cm3) = 15.3 g
• 4. A gas has a density of 7.44g/L. What is that in

       7.44 g x 1 L     x 1 mL x (10 cm)3 = 7.44 g/dm3
         L     1000mL     1 cm3    (1 dm)3
Density in lab
• 5. A copper ball has a mass of 9.98g. What would
   you do in a lab experiment to determine the density?
• -Water displacement: Fill a grad. cylinder ~half full of water.
  Take the reading. Place the copper ball in the cylinder. Take
  new reading. Subtract the two to get volume. Divide mass by
  volume to get density.
• If Vinitial = 6.21mL and Vfinal= 7.70mL,what is density?
• 9.98g/(7.70mL-6.21mL)= 6.70g/mL
• 6. The theoretical value for the density of copper is
   8.96g/cm3. What is the percent error of the above

                                                   (8.96-6.70) x 100
• 99.9% of gas to liquid to solid substances become more dense.
• SOLID      >        LIQUID         >       GAS

• ONE substance follows a different pattern:

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