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Chemistry LibreTexts

1.7: Density

  • Page ID
    152315
  • Learning Objectives

    • Define density.
    • Determine the density of various substances.

    Density (\(\rho\)) is a physical property found by dividing the mass of an object by its volume. Regardless of the sample size, density is always constant. For example, the density of a pure sample of tungsten is always 19.25 grams per cubic centimeter. This means that whether you have one gram or one kilogram of the sample, the density will never vary. The equation, as we already know, is as follows:

    \[\text{Density}=\dfrac{\text{Mass}}{\text{Volume}}\]

    or just

    \[\rho =\dfrac{m}{V}\]

      Table \(\PageIndex{1}\) Densities of Common Substances
    Substance Density at 25°C (g/cm3)
    blood 1.035
    body fat 0.918
    whole milk 1.030
    corn oil 0.922
    mayonnaise 0.910
    honey 1.420

    Notice in Table \(\PageIndex{1}\) that corn oil has a lower mass to volume ratio than water. This means that when added to water, corn oil will “float.”

    Density can be measured for all substances, solids, liquids and gases. For solids and liquids, density is often reported using the units of g/cm3. Densities of gases, which are significantly lower than the densities of solids and liquids, are often given using units of g/L.

    Example \(\PageIndex{1}\): Ethyl Alcohol

    Calculate the density of a 30.2 mL sample of ethyl alcohol with a mass of 23.71002 g

    Solution

    \[\rho = \dfrac{23.71002\,g}{30.2\, mL} = 0.785\, g/mL \]

    Exercise \(\PageIndex{1}\)

    1. Find the density (in kg/L) of a sample that has a volume of 36.5 L and a mass of 10.0 kg.
    2. If you have a 2.130 mL sample of acetic acid with mass 2.234 g, what is the density in g/mL?
    Answer a
    \(0.274 \,kg/L\)
    Answer b
    \(1.049 \,g/mL\)

    Summary

    • Density is defined as the mass of an object divided by its volume.

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