How can density be found by water displacement?

The mass of an empty volumetric cylinder is 120g. After adding a bolt, the mass becomes 128g and the mass after the addition of water to the 57mL mark is 183g. What is the density of the bolt?
B. Coulter

1. Identify the unknown. You want the density of the bolt.
2. List the given information. You have masses of the cylinder, cylinder with the bolt, and cylinder with the bolt and added water. You know the volume of the bolt and the water together must be 57 mL.
3. Connect the given information with the target. It's best to work backwards from the target. Density of the bolt is the mass of the bolt divided by the volume of the bolt.
• The mass of the bolt is just the mass of the cylinder and bolt (128 g) minus the mass of the cylinder (120 g).
• The volume of the bolt is the volume of the water plus bolt (57 mL) minus the volume of the water. You must find the volume of the water:
• The water mass is the mass of cylinder and bolt and water (183 g) minus the mass of the cylinder and bolt (128 g), or 55 g.
• The density of water is approximately 1.00 g/mL, so the volume of water is 55 g/1.00 g/mL = 55 mL.
...the volume of the bolt must be 2 mL.
• The density of the bolt must be 8 g / 2 mL or 4 g/mL.

Author: Fred Senese senese@antoine.frostburg.edu

General Chemistry Online! How can density be found by water displacement?