What is Density | Chemistry for EmSAT Achieve PDF Download

Introduction

Density is a fundamental measurement comparing the amount of matter an object possesses to its volume. It essentially indicates how tightly packed matter is within an object. It's a unique physical property discovered by the Greek scientist Archimedes.

• Density quantifies how closely packed a material is, expressed as mass per unit volume.
• Denoted by D or ρ, the formula for density is ρ = m/V, where ρ represents density, m is mass, and V is volume.

Examples of Density

Dense materials like iron, platinum, and lead have high mass in a specific volume, whereas sparse materials like glass and bamboo have lower mass in the same volume. Generally, solids are denser than liquids, and liquids are denser than gases.

Calculating Density

Mathematically, density (ρ) is determined by the ratio of mass (m) to volume (V). The SI unit for density is kilograms per cubic meter (kg/m³), but for convenience, different units are used for solids, liquids, and gases. 


Where, ρ is the density, m is the mass and V is the volume

Applications in Real Life

Density finds applications in various fields like pipe design, shipbuilding, and aviation. Knowledge of densities aids in separation techniques, such as separating oil from water in case of spills. Moreover, it determines whether objects float or sink in fluids.

Example

Q1: If you find a shiny rock, a carbon allotrope with a volume of 0.042 cm³ and a mass of 0.14 g, is it graphite or diamond? The density of graphite is 2.266 g/cm³ and the density of diamond is 3.51g/cm³.
Sol: Given,
Volume of the shiny rock =0.042 cm³ 
Mass of the shiny rock = 0.14 g
Density of graphite = 2.266 g/cm³ 
Density of diamond = 3.51g/cm³
Use the density equation to solve for m, for the mass of graphite and for the mass of a diamond.
ρ = m/V
m = ρV
m = 2.266 g/cm³ x 0.042 cm³ = 0.0951g for graphite
m = 3.51g/cm³ x 0.042 cm³ = 0.1474 g for diamond
The mass of the shiny rock you found is identical with the mass of diamond.

Q2: Calculate the density of water if it has a mass of 1160 Kg and a volume of 1 m³?
Sol: Given,
Mass = 1160 Kg
Volume = 1 m³
Density is given by the formula:
Density = Mass/Volume
ρ = 1160/1 = 1160 kg/m³