Density and % error

Density Density – Compares mass (amount of matter) of object to its volume (amount of space occupied) mass per unit volume (g/cm 3 ) D = MVMV D M V

Density Mass is always in g Volume is always in cm 3 If not… you must convert Note: I L = 1dm 3 1mL = 1 cm 3 g/ cm 3 Is considered to be a derived unit because it combines 2 SI units

Example Calculate the density of an object that has a volume of 4.67 cm 3,and a mass of 56.9 g D = m V D= x M= 56.9g V= 4.67 cm 3

Examples X = 56.9g 4.67 cm 3 x=12.2 g/cm 3 * RULE FOR SIGNIFICANT DIGITS WHEN MULTIPLYINMG OR DIVIDING APPLY HERE

Density An object has a volume of 825 cm 3 and a density of 13.6 g/cm 3. Find its mass. GIVEN: V = 825 cm 3 D = 13.6 g/cm 3 M = ? WORK : M = DV D M V

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 D M V WORK : V = M D

Density You have a sample with a mass of 620 g & a volume of 753 cm 3. Find density. GIVEN: M = 620 g V = 753 cm 3 D = ? D M V WORK : D = M V

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

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/cm 3

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?

% 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