How dense is oil

Density of oil and water

Oil is lighter than water, so it floats on water

In everyday life one often hears “Oil (and by that we often mean cooking oil) is“ lighter ”than water and therefore floats on water”. Here we should already take into account that this statement “lighter” does not mean the weight, but the density of the liquid. Nevertheless, the statement corresponds to the scientific facts:

We can prove this with a simple experiment: we put some cooking oil in a glass and then water and in the second experiment we put cooking oil in a glass with water. We always observe the same result: water and cooking oil are two (with each other) immiscible liquids. Therefore, two layers form in the glass (a water layer and an oil layer). Due to the lower density of edible oil, the edible oil always forms the upper layer and the water the lower layer.

But not every oil floats on water, so there are also oils (heavy oils such as tar) that do not float on water, but sink. In such a case, the water will float on the oil. In order to be able to judge whether an oil floats or submerges on the water, we have to know (or calculate) the density of the oil.

Determining the density of liquids

The definition for density says and that this quantity indicates the weight per volume of a liquid. Therefore (if we want to determine the density of an oil) we have to measure two quantities. The weight of a given amount of oil, as well as the volume that that amount of oil takes up.

  • In the first step we weigh a beaker (there must be a volume scale on the beaker so that we can read the volume) with a scale.
  • Then we pour a certain amount of oil into the beaker and read the added volume on the scale on the beaker.
  • Now the beaker with the oil is weighed and the difference between (beaker with oil) and (empty beaker) is calculated.
  • Now we calculate the density of the liquid by dividing the mass of the oil by the volume (here: 1 ml = 1 cm³)

In this case we will find that the density of edible oils is less than 1 g / cm³. Since water has a density of around 1 g / cm³, (edible) oil is lighter than water and therefore “floats” on the water

When does oil float on water?

How can you judge whether an oil floats on the water or goes down?
Now that we have determined the density of the oil, we can answer that question

  • If the density of the oil is greater than the density of water (1 g / cm³), the oil will sink.
  • If the density of the oil is less than the density of water (1 g / cm³), the oil floats on the water.

As we saw when determining the density (density = mass: volume), the size of the liquid or body does not matter.

Since many oils have a density of around 0.8 to 0.9 g / cm³ and (a lower / lower density than water) are immiscible with water, oils float on the water and do not sink. For this reason, density is also an important property of substances in order to classify substances into individual substance classes or to differentiate substances.