Density is the mass--that is, the amount of matter--in
a unit volume of any substance. The density of a substance
is found by dividing its mass by its volume. The density
of a liquid or solid is measured in grams per millilitre.
The density of a gas is measured in grams per litre.
The concentration of a substance in a solution can be determined
by measuring the density of the solution. Density measurements
are useful in identifying minerals and other solids. In
addition, the molecular weight of a gas can be calculated
from its density .
The density of a liquid can be determined by measuring
the mass needed to fill a container of a known volume. In
most cases, a device called a pycnometer, which has a precisely
known volume, is used for this purpose. An instrument called
a hydrometer is also used to determine the density of a
The density of a regularly shaped solid is determined by
simply measuring the object's mass, calculating its volume,
and dividing the mass by the volume. The density of an irregularly
shaped solid is determined by submerging it in a known quantity
of liquid and measuring the volume of the liquid displaced.
The volume of the displaced liquid equals the volume of
the solid. The mass of the object is then determined and
is divided by the volume.
The density of a gas is difficult to measure because it
is extremely low and changes greatly with variations in
temperature and pressure. The mass of a gas can be determined
by subtracting the mass of an empty container from the mass
of the same container when filled with the gas. The volume
of the container can simply be found by measuring the amount
of water (using a graduated flask) that the container holds.
The specific gravity of a substance is related to its density.
Specific gravity is the ratio of the mass of a given volume
of the substance to the mass of an equal volume of water.
It is found by dividing the density of the substance by
the density of water at either 4 °C or 20 °C.
A quick look at Density
It is the simple ratio between mass and volume of a substance.
CGS unit of density - gm/cm3
MKS unit of density - kg/m3
1gm/cm3 = 1000 kg/m3
Finding density of a regular solid
Mass = 50kg , volume = length * breadth* height = 20m
Density = mass/volume
=2.5 kg / m3
Finding density of an irregular solid
Calculate their masses
Volume of the body = (y-x)cm
Density = mass/volume = m/y-x
X cm3 y cm3
Determination Of Density Of A Liquid
Mass of an empty bottle - m1 gm
Mass of bottle with water - m2 gm
Take out the water dry the water and fill the bottle with
the liquid whose density is to be taken.
Mass of bottle filled with liquid - m3 gm
Mass of water - (m2 - m1) gm
Mass of liquid - (m3 - m1) gm
Density of water = 1gm/cm3
Density = mass / volume v = m/d
Volume of water = m2 - m1 / 1gm/cm3
Volume of liquid = volume of liquid (as they were contained
in the same vessel)
Volume of liquid = m2-m1 cm3
Density of liquid = m3-m1 / m2-m1
Finding density of air
Take an empty (vacuum) vessel flask and note its
mass = m1 gm
Mass of flask filled with air = m2 gm
Volume of air filled in flask = V cm3
Mass of dry air = (m2 - m1) gm
Density of air = m2-m1/V