# Relative Density of Substances and Specific Gravity

### Relative Density (Specific Gravity):

Density is an important unit of measurement. This is so because equal volumes of different substance have got their respective masses and weights.

Density is defined as the mass of a unit volume of a material or substance. An understanding on density will aid you to better comprehend the concept of relative density.

Relative density involves the density of one substance in relation to that of water (at 4oC). It is also called specific gravity.

The Relative Density (R.D) of a material is the ratio of it's density (the material) to that of water at 4oC.

By principle, an object with a specific gravity or relative density of less than 1 will float on water, while that with value greater than 1 will sink in water.

Below is a summary of formulas for calculating Relative Density:

• Relative Density (R.D) = Mass of Substance/Mass of Water at 4oC

• R.D = Weight of Substance/Weight of Water

• R.D = Density of Substance/Density of Water at 4oC

• R.D = ρsubstance / ρreference (water at 4oC)

• Where ρ = Density

Relative Density has no Standard International (SI) unit.

The table below shows the Relative Density of some substances:

 Substance Relative Density Balsa Wood 0.2 Oak Wood 0.75 Ethanol (C2H5OH) 0.78 Liquid Paraffin 0.8 Olive Oil 0.91 Coconut Oil 0.925 Petroleum 0.98 Water (Fresh Water) 1 Salt Water (Reef Aquarium) 1.025 Ironwood 1.5 Graphite 1.9 – 2.3 Common  Salt (NaCl) 2.17 Aluminium (Al) 2.7 Cement 3.15 Iron  (Fe) 7.87 Copper (Cu) 8.96 Lead (Pb) 11.35 Gold (Au) 19.3 Osmium (Os) 22.59

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