Relative density

Relative density, also known as specific gravity, is the ratio of a substance’s density (mass per unit volume) to the density of a reference material. Water at its densest temperature (4 °C or 39.2 °F) is generally always used as a reference for liquids, while air at ambient temperature (20 °C or 68 °F) is used for gases. The term “relative density” is commonly used in scientific circles.

Factors affecting relative density

As previously stated, relative density is a ratio of a substance’s density to the density of water. As a result, any change in the density of either the substance or the water will impact the relative density ratio. The factors that affect the density of any material and hence indirectly affect relative density are listed below. 

Temperature

Because the mass doesn’t change unless we add more of the same material to it, the density will vary if the volume changes. When the volume of a substance is increased, the density decreases, and vice versa. We can change the volume of a substance by heating or cooling it. Because volume is inversely related to density, it will adjust its density correspondingly. As a result, increasing the temperature has an inverse relationship with increasing the density, because increasing the temperature increases the volume. 

Pressure

Consider taking a glass of water from earth to space, where the lack of pressure causes it to evaporate as quickly as possible. However, when the volume increases, the density drops. As we increase the pressure, the density increases proportionally because the force of attraction between the molecules stronger and the intermolecular gaps shrink, resulting in a higher density. As a result, we can say that pressure is proportional to material density.

Nature of substance

As can be seen from the formula, density is a property of all materials, and so relative density is completely reliant on the nature of the substance as well as the nature of water at a given temperature.

Relative density equation

A substance’s density is defined as its mass per unit volume. ρ is the symbol . If a material’s mass is M and its volume is V, the density of the substance is calculated as follows:

ρ=M/V

The kilogramme per cubic metre (kg/m³) is the SI unit for density. 

Relative Density of Liquids: Device to Measure

A hydrometer is used to determine the relative density of a liquid. This gadget works on Archimede’s principle, which states that when a body is totally or partially immersed in a liquid, it receives an upward force proportional to the weight of the fluid displaced.

A hydrometer is a glass instrument with a stem and a bulb. The hydrometer’s bulb is filled with mercury or lead shot. It floats in the upright position as a result of this. To measure relative density, the hydrometer is slowly placed into the liquid until it floats freely. The relative density of a liquid is determined by the point at which its surface meets the hydrometer’s stem.A lactometer is a hydrometer that is used to determine the purity of milk.

Relationship between relative density and density

In the SI system, the relative density of a substance is calculated by multiplying its density by 1000.

RD= Density Of The Substance In Kgm^-3/ 1000Kgm^-3

Density Of A Substance = (RD×1000)Kgm^-3

The density of a substance in the CGS system is given by.

Density = (RD×1)Gcm^-3

Floating and sinking

When an object is submerged in a liquid, its density determines whether it will float or sink. The object will sink in the liquid if its density is greater than the density of the liquid. The object will float on liquid if the density of the liquid is greater than the density of the object. For example, if we put a steel spoon in a bucket of water, the spoon would sink because its density is greater than that of the water, however if we put a plastic ball in the same bucket of water, the plastic ball will float on the surface since its density is lower than that of the water.A substance with a relative density of less than one will float on water’s surface. Wood and kerosene, for example. In water, substances with a relative density greater than one sink. Iron and aluminum, for example.

Conclusion

The density of a substance is a property that describes how tightly the particles are packed in a particular volume of the substance. The density of an object increases as it becomes heavier. When the temperature of a substance is increased, the density of the substance falls, and when the temperature is dropped, the density of the substance increases.A substance’s relative density is commonly used to compare its density to that of water. It also aids in the verification of a substance’s purity.