Question

Why is the density of seawater more than that of rainwater?

Answer 1

Hint: Using the relation between density and mass and knowing the difference in nature of seawater and rainwater we can answer this question. Seawater has salts present in it unlike rainwater and these ions make seawater heavier.

Complete step by step answer:
Rainwater is the pure form of water whereas Seawater is not pure and contains salt and minerals, some smaller amounts of other substances which include dissolved organic and inorganic substances, some particulates, and some of the atmospheric gases. These salts and ions increase the mass of seawater.

The density of seawater increases with a decrease in temperature whereas the density of pure water decreases with a decrease in temperature. The density of seawater increases as pressure increases so as the depth of the ocean increases pressure increases hence density at depth is more than that at the surface.We know,
\[\text{density} = \dfrac{\text{mass}}{\text{volume}}\]
This gives us the relation between density and mass
$\text{density} \propto \text{mass}$
Since the mass of seawater is more than that of rainwater. So for the same volume of seawater and rainwater, the density of seawater will be more than that of rainwater.

Note: The density of salty water is \[1023.6{\text{ }}\dfrac{{kg}}{{{m^3}}}\] at a temperature of \[{25^ \circ }C\] salinity of $35\dfrac{g}{{kg}}$ , and pressure of $1atm$. The density of freshwater is \[1000\dfrac{{kg}}{{{m^3}}}\] . Also, the freezing point of seawater is lower than that of freshwater due to variations in salinity. The saltiness of a body of water, or the amount of salt dissolved in it, is referred to as salinity.