Chapter 2 · Measurement and Problem Solving
2.10Density
12 min · two checks
Predict
A metal block has a mass of 156 g and a volume of 20.0 cm³. Will it sink in water?
The idea
- Calculate density and use it as a conversion factor.
- Compare a solid’s density with water’s.
Density is mass divided by volume, d = m/V. It is a property of the material at a stated temperature, not a property of how big the chunk is. A large piece of cork can be heavier than a small piece of lead and still be less dense. Water near room temperature is about 1.00 g/mL, so densities in g/mL are also specific gravities relative to water, roughly. Ice is slightly under 1 g/mL, which is why it floats.
Because density ties mass and volume, it is a conversion factor. 7.80 g/cm³ means 7.80 g = 1 cm³ for that metal. You can find the mass of a given volume or the volume of a given mass without a new experiment. Report the units. A bare “7.8” is not a density.
Keep these
- d = m/V. Common lab unit: g/mL or g/cm³.
- Density converts mass ↔ volume for a stated substance.
- Objects less dense than the surrounding liquid float.
Worked path
Ethanol has density 0.789 g/mL. What mass of ethanol occupies 45.0 mL?
Observe
d = 0.789 g/mL, V = 45.0 mL. Want mass.