Question

Why is the seawater denser than freshwater?

Answer 1

Hint : Seawater consists of $96.5{\text{ \% }}$ water, $2.5{\text{ \% }}$ salts, and smaller amounts of other substances like dissolved inorganic and organic materials, particulates, and a few atmospheric gases. Freshwater Is naturally occurring water other than sea/ocean water like ponds, lakes, rivers,, etc. it has $0.05\%$ salt and some dissolved minerals.

Complete Step By Step Answer:
Density is the mass of a material per unit volume. Adding any small substance to a liquid may not necessarily change its volume but definitely, there will be a change in its mass. This is the same case observed between seawater and freshwater. Seawater contains $3.5\%$ which is $35000$ ppm of salt in it. The little amount of salt doesn’t make any visible change in its volume but its mass is increased. Whereas in case of freshwater, it does not contain salt or its quantity is very less may be less than $500$ ppm (parts per million), so this will not make a visible difference in the mass of fresh water and neither there is a change in its volume. Hence salt present in seawater makes it denser than freshwater.

Additional Information:
There is a sea on the border between Israel and Jordan, it is known as the Dead Sea. The name is quite weird but it is there. This sea has the highest concentration of salt, fluctuating around $31.5\%$ . This concentration is very much higher compared to the normal value because of the high concentration of salt in it; its density is also very high around $1024$ kg/l than the normal seawater which is $1.025{\text{ }}$ kg/l. This high concentration results in providing natural buoyancy to the water and one can float on it without any support.

Note :
If there is even a little amount of substance present in water its mass will get affected and will make it slightly denser. So the presence of salt in more amounts in seawater makes it denser than freshwater. With little concentration of salt, there will not be any change in the volume or the change will be so less that it can be neglected.