Calculating Density - Worked Example Problem

Density is a measure of how much matter is in a space. It is expressed in units of mass per volume, such as g/cm3 or kg/L. This is a worked example of how to calculate the density when given the volume and mass of a substance. Sample Density Problem A brick of salt measuring 10.0 cm x 10.0 cm x 2.0 cm weighs 433 grams. What is its density?Solution:Density is the amount of mass per unit volume, or:D M/VDensity Mass/VolumeStep 1: Calculate VolumeIn this example, you are given the dimensions of the object, so you have to calculate the volume. The formula for volume depends on the shape of the object, but its a simple calculation for a box: Volume length x width x thicknessVolume 10.0 cm x 10.0 cm x 2.0 cmVolume 200.0 cm3Step 2: Determine Density Now you have the mass and the volume, which is all the information you need to calculate density.Density Mass/VolumeDensity 433 g/200.0 cm3Density 2.165 g/cm3Answer:The density of the salt brick is 2.165 g/cm3. A Note About Significant Figures In this example, the length and mass measurements all had 3 significant figures. So, the answer for density should also be reported using this number of significant figures. Youll have to decide whether to truncate the value to read 2.16 or whether to round it up to 2.17.