# What is the density of tap water and how can a property such as density be used to identify an unknown substance?

Oct 6, 2016

The density of water is $1 \cdot g \cdot c {m}^{-} 3$.

#### Explanation:

$\text{Density, } \rho$ $=$ $\text{Mass"/"Volume}$. We assume a standard temperature of $298 \cdot K$.

${\rho}_{\text{water}}$ is conveniently 1:1 with respect to volume and mass given appropriate units of mass and volume.

As liquids go, water is exceptionally dense, a property attributable to hydrogen bonding, and the strong intermolecular forces that exist between water molecules. Most organic solvents will float on water, and thus necessarily have $\rho < 1 \cdot g \cdot c {m}^{-} 3$.

The density of mercury metal is $13.55 \cdot g \cdot c {m}^{-} 3$. Will mercury float on water? The density of a pound coin is approx. $8 \cdot g \cdot c {m}^{-} 3$. Will a pound coin float on mercury metal?

If you have a table of densities, sometimes you can identify the substance if you measure its density. Usually, there are other more convenient means of identification.