Final answer:
Impure water has a greater density than pure water because the dissolved impurities add mass without significantly increasing volume, leading to an increase in density. Minerals, salts, and contaminants contribute to this increased density, aligning with the principle that substances with a relative density greater than 1 are denser than water.
Step-by-step explanation:
The statement that the density of impure water is greater than that of pure water can be justified by considering the impurities dissolved in water. Pure water is a benchmark with a density of 1 g/cm3 at 4°C. However, when substances are dissolved in water, these substances can increase the mass of the solution without significantly changing its volume, hence increasing its density.
For example, when impurities such as minerals, salts, or other contaminants are dissolved in water, they add to the mass of the water mixture. Since density is the mass per unit of volume, if the mass increases while the volume remains relatively constant, the density of the water will naturally increase. This is why polluted water or water with a high mineral content can have a higher density than pure water. The phenomenon clearly reflects the concept that substances with a relative density greater than 1 will sink in water, just as impurities added to water will make it denser.