Question

How can density be used to identify substances?

Answer 1

You can identify an unknown substance by measuring its density and comparing your result to a list of known densities.

Density = mass/volume. Assume that you have to identify an unknown metal. You can determine the mass of the metal on a scale. You can determine the volume by dropping the object into a graduated cylinder containing a known volume of water and measuring the new volume. You divide the mass by the volume and compare the density to a list of known densities.

EXAMPLE

A metal bolt with a mass of 99.7 g is dropped into a graduated cylinder containing 50.0 cm³ of water. The new volume reads
72.1 cm³. Identify the metal.

Solution

V = 72.1 cm³ - 50.0 cm³ = 22.1 cm³

D = `m/V = (99.7 g)/(22.1 cm³)` = 4.51 g/cm³

Now you compare your density with a list obtained from your instructor or from an on-line source such as

https://sites.google.com/site/chempendix/densities-of-pure-metals

What metal was your bolt made of?