Density

Litre elements and compounds have their unique densities associated with them. The density of a matter is one of its physical characteristics. In simpler words, the ‘heaviness’ of objects with a constant volume can be said to be a qualitative measurement of the density of that object. So it can be said that the compactness of mass in a substance is what its density is all about. 

It is the sole reason some things sink while others float in a different medium. A very common example, in this case, is that of a helium balloon floating in the air. This happens because the gas helium is less dense when compared to the air in the atmosphere. Thus, a helium balloon can float in the air.

Definition of Density

The density of an object is the ratio between its mass and per unit volume. It describes how dense material is in a specified area. The Greek scientist Archimedes was the one who put forth this concept which is so widely applied in various fields. 

The symbol of the density of an object is D or ρ. The formula used to calculate the density of an object is expressed as 

ρ = m/v

Here, ρ = the object’s density,

m = the mass of the object, and

V = the object’s volume

Unit of density

Density is a quantitative measurement of the compactness of an object. So, it needs to be expressed in units. Many units of density can be used.

The SI unit of density is kg/m³. For ease of use, the unit used to express the density of the gas is g/cm³. Likewise, for liquids, g/ml, and for gases, g/L is used for convenience. 

In the CGS system, density is measured in grams per cubic centimetre (g/cm3).

There are other units to express density as well. However, they are not a part of the SI unit system. These units are stated as follows – 

• gram per cubic centimetre (g/cm3)
• 1 g/cm3 = 1000 kg/m3
• kilogram per cubic decimeter (kg/dm3)
• gram per millilitre (g/mL)
• metric ton per cubic metre (t/m3)
• kilogram per litre (kg/L)

Densities of Some Common Elements and Compounds

The density of some common substances are stated as follows – 

Application of density

The density of a substance is one such physical property of it that has many applications around use. We probably come across it every day without even knowing it. Let us discuss a few of its common applications in the following points – 

Aeroplanes 

Although the primary force that helps the aeroplane is pressure and velocity, density also has an important role to play in it. The aircraft’s weight distribution is designed in a manner that makes its density not uniform. This results in the shifting centre of the mass.

Ships and submarines

It is already known to us by now that if an object is less in density than water, then it will float. If it is denser than water, it will sink. Ballast tanks containing air are installed in ships that aid in decreasing the density of the ship, and thus, it floats. On the other hand, submarines fill in their ballast tanks with water to submerge underneath when required. 

Purification of objects

Several mixtures are made to float in water to identify and segregate the different objects depending on the varying density.

Plumbing system

While designing dams and large plumbing projects, engineers widely used the tool of density in estimating certain aspects.

Oil spills

Oil spills are hazardous to marine life. Since oil floats on water, it makes it easier to clean up.

Measuring density

As discussed earlier, density is measured by the formula 

ρ =m/v 

Example 1: Find the density, in g/cm3, of a metal cube with a mass of 55.0 g and an edge length of 2.70 cm.

Solution: Edge length of the cube = 2.70cm

• the volume (V) = (2.70 cm)3

 = 19.7 cm3

Now that we know the volume,

Density (ρ) of the cube = 55.0/19.7 g/ cm3

= 2.80 g/cm3

Example 2: The density of lead is 11.342 g/cc. What would be the volume of a 120.0 g sample of this metal?

Solution: Density = 11.342g/cc

Mass = 120.0 g

• Volume = 11.342/120.0 cc or cm3

= 0.0945 cc or cm3

Example 3: How many kilograms of mercury will fill a 5-litre container if the density of mercury is 13.6 grams/centimeter³?

Solution: The container can hold 5l of water.

Density of mercury = 13.6 g/cc

• Mass of the mercury = 13.6 g/cc ÷ 5 l

= 68 kg

Conclusion

Density is an important concept in chemistry. It is used in various aspects of life. Even the formation of clouds works on this mechanism. Pharmaceutical companies, chemical, petrochemical, and even food and beverage industries frequently measure the densities of the various raw materials used in their manufacturing.