Download - Density and % error
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Density and % error
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Density
• Density – Compares mass (amount of matter) of object to its volume (amount of space occupied)
• mass per unit volume (g/cm3)
D = MV D
M
V
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Density
• Mass is always in g
• Volume is always in cm3
• If not… you must convert
• Note:
• I L = 1dm3
• 1mL = 1 cm3
g/ cm 3
Is considered to be a derived unit because it combines 2 SI units
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Example
• Calculate the density of an object that has a volume of 4.67 cm3,and a mass of 56.9 g
• D = m V
• D= x• M= 56.9g• V= 4.67 cm3
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Examples
• X = 56.9g
4.67 cm3
• x=12.2 g/cm3
• * RULE FOR SIGNIFICANT DIGITS WHEN MULTIPLYINMG OR
DIVIDING APPLY HERE
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Density
• An object has a volume of 825 cm3 and a density of 13.6 g/cm3. Find its mass.
GIVEN:
V = 825 cm3
D = 13.6 g/cm3
M = ?
WORK:
M = DV
DM
V
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Density
A liquid has a density of 0.87 g/mL. What volume is occupied by 25 g of the liquid?
GIVEN:
D = 0.87 g/mL
V = ?
M = 25 g
DM
V
WORK:
V = M D
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Density
You have a sample with a mass of 620 g & a volume of 753 cm3. Find density.
GIVEN:
M = 620 g
V = 753 cm3
D = ?
DM
V
WORK:
D = M V
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Ways to determine density
1. Regularly shaped objects – direct volume measurement (l x w x h)
2. Irregularly shaped objects- use water displacement method (graduated cylinder) to find volume.
Note: mass is found the same way regardless the shape of the object
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Density
• I have a block that measures 5.25 cm by 2.25 cm by 8.50 cm.
• I weigh the block and find its mass to be 5.85 g
• Calculate the density of the block in g/cm3
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For example
• A chunk of metal has a mass of 5.25 g. It is placed in a graduated cylinder containing 25.0 ml of water. Once the metal is placed in the graduated cylinder, the water rises to 38.2 ml. What is the density of the metal?
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% error
• % error – the deviation from the accepted value during an experiment. Usually caused by human error.
• % error = (your value - literature value) x 100
• literature value
• It is always a positive number
Page 38 in textbook has a list of densities