Density

What is Density? It is an example of a physical property of matter Each element and compound has a unique density. It is expressed quantitatively. It refers to how closely "packed" or "crowded" the material appears to be

Density Comparison to Water In chemistry, we compare the density of a substance to the density of water. Does an object float on water or sink in the water? If an object such as a piece of wood floats on water it is less dense than water. If a rock sinks, it is more dense than water.

Ex. 1) Oil and vinegar salad dressing The oil floats on the vinegar water mixture, while the solids sink to the bottom. Which is LESS DENSE? Oil or Vinegar?

Ex. 2) Oil spills What happens when an oil tanker leaks on the ocean? The oil floats on the water since it is less dense This provides some opportunity to clean up the oil spills by skimming the oil from the surface of the water

Ex 3) Ice Recall: Ice floats on water (but did you know that this is an abnormal physical property of solid/liquid state of water?) Most solids are more dense than its own liquid version However, ICE is LESS DENSE than WATER!

Mathematical Definition of Density density is the amount mass in a given amount of space Therefore, we must know the mass and the volume to calculate density Density = mass (g)   volume (mL)

Example 1) Calculate the density in g/mL of aluminum if a 50 mL block weighs 135 g. Round answer to two dp. Density = mass VOLUME = 135 g    50 mL =2.70 g/mL Therefore, the density of the aluminum is 2.70 g/mL.  

Example 2) You have a rock with a volume of 15cm3 and a mass of 45 g. What is its density?

Solution Mass = 45 g Volume = 15 cm3 Density = ? Density = mass volume = 3.0 g/cm3

Example 3) If the density of an unknown solid is 4.50g/cm3, how much mass would take up 5.00 cm3 worth of space?

Example 4) If the density of an unknown liquid is 2.50g/mL, what volume would hold 5.00g of this unknown.