Chemistry / Chem 0107 · Procedure · 60–90 seconds
Calculating Density from Mass and Volume
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Calculating density means measuring an object's mass and volume separately, by balance and by geometry or displacement, then dividing mass by volume, carrying the unit through the division.
A metal cube with an edge length of 2.00 cm has a volume of 2.00 × 2.00 × 2.00 = 8.00 cm³. If the cube's mass on a balance reads 90.7 g, its density is 90.7 g ÷ 8.00 cm³ ≈ 11.3 g/cm³, a figure that already reflects three significant figures. A liquid sample poured into a graduated cylinder shows a similar pattern: 45.0 mL of an unknown liquid with a mass of 35.6 g yields 35.6 g ÷ 45.0 mL ≈ 0.791 g/mL, a value low enough to suggest an alcohol rather than water.
Students sometimes invert the ratio, dividing volume by mass instead of mass by volume, which produces a reciprocal unit like cm³/g instead of g/cm³ — checking that the result's units read mass over volume catches the error immediately.