Question

Which of the following controls the density of seawater?
A) Temperature
B) Salinity
C) Both A and B
D) None of these

Answer 1

Hint: Seawater has unique properties, that is, it is saline, its freezing point is slightly lower than freshwater, its density is slightly higher, its electrical conductivity is much higher, and it is slightly basic. Seawater makes up the oceans and seas, covering more than 70 percent of Earth’s surface.

Complete answer:
There are mainly two factors that make ocean water more or less dense than about $1027 kg/m^3$.
The temperature and salinity are the two properties of seawater that control the density of the seawater. If temperature reduces, the density of water increases. If salinity increases, the density of seawater also increases.

Seawater comprises a rich source of various commercially significant chemical elements. The World’s most magnesium is recovered from seawater, as are large quantities of bromine. Sodium chloride (table salt) is still obtained by evaporating seawater in some parts of the world. Both temperature and salinity control the density of seawater.

Therefore the correct answer is option ‘C’.

Note: Seawater is a complex mixture of 96.5 percent water, 2.5 percent salts, and lesser amounts of other particles, consisting of dissolved inorganic and organic materials, particulates, and a few atmospheric gases. The presence of salts in seawater influences most physical properties of seawater like density, compressibility, freezing point and temperature of the density maximum to some degree but does not determine them. At a temperature of 25 °C, the salinity of 35 g/kg and 1 atm pressure, the density of seawater is $1023.6 kg/m^3$.