Introduction to Density  Density is the measurement of the mass of an object per unit volume of that object. d = m / V  Density is usually measured in g/mL or g/cm 3 for solids or liquids.  Volume may be measured in the lab using a graduated cylinder or calculated using:  Volume = length x width x height if a box or  V =  r 2 h if a cylinder.  Remember 1 mL = 1 cm 3

How to measure the density of a solid in the laboratory. Obtain a clean graduated cylinder. Fill the graduated cylinder with enough water to cover the object. Record the volume Carefully place the object into the water filled graduated cylinder. Record the new water level. The volume of the object is the V final – V initial.

Introduction to Density Example: An object has a mass of 50.0 g and occupies a volume of 52.0 mL. What is its density? d = m / V = 50.0 g / 52.0 mL = 0.98 g/mL Example: A cylinderical piece of metal is 2.03 inches high and has a diameter 17.0 mm wide and weighs g. Identify the metal. V=  r 2 h =  (1.70 cm/2) 2 * (2.03 in [2.54 cm/1in]) =11.7 cm 3 D = m/V = g / 11.7 mL = 2.70 g/mL The metal is aluminum!

Practice Problems on density ___________ 1. Calculate the volume, in microliters, of a cylinder that is mm long with a diameter of cm. ___________ 2. Calculate the density of a solution if 45.0 mL of the solution weighs 7.12 x kg. ___________ 3. The Hope diamond weighs carats and has a density of 3.51 g/cm 3. What is the volume of this diamond? (1 carat = 200 mg) ___________ 4. A plastic material weighing 2.2 lb is shaped into a cylinder 13.5 cm in height and 6.8 cm in diameter. Will this object sink or float in water? ___________ 5. A student fills a 50.0 mL graduated cylinder with 25.0 mL of water, then places a spherical object weighing g into the graduated cylinder. The new volume is 41.5 mL. Calculate the density of the object g/mL 2.59 cm g/cm 3 ; sink 1.58 g/mL 15.9  L