<P> Seawater , or salt water , is water from a sea or ocean . On average , seawater in the world 's oceans has a salinity of about 3.5 % ( 35 g / L , 599 mM ) This means that every kilogram ( roughly one litre by volume ) of seawater has approximately 35 grams ( 1.2 oz ) of dissolved salts ( predominantly sodium ( Na + ) and chloride ( Cl − ) ions ) . Average density at the surface is 1.025 kg / L. Seawater is denser than both fresh water and pure water ( density 1.0 kg / L at 4 ° C ( 39 ° F ) ) because the dissolved salts increase the mass by a larger proportion than the volume . The freezing point of seawater decreases as salt concentration increases . At typical salinity , it freezes at about − 2 ° C ( 28 ° F ) . The coldest seawater ever recorded ( in a liquid state ) was in 2010 , in a stream under an Antarctic glacier , and measured − 2.6 ° C ( 27.3 ° F ) . Seawater pH is typically limited to a range between 7.5 and 8.4 . However , there is no universally accepted reference pH - scale for seawater and the difference between measurements based on different reference scales may be up to 0.14 units . </P>
<P> Seawater , or salt water , is water from a sea or ocean . On average , seawater in the world 's oceans has a salinity of about 3.5 % ( 35 g / L , 599 mM ) This means that every kilogram ( roughly one litre by volume ) of seawater has approximately 35 grams ( 1.2 oz ) of dissolved salts ( predominantly sodium ( Na + ) and chloride ( Cl − ) ions ) . Average density at the surface is 1.025 kg / L. Seawater is denser than both fresh water and pure water ( density 1.0 kg / L at 4 ° C ( 39 ° F ) ) because the dissolved salts increase the mass by a larger proportion than the volume . The freezing point of seawater decreases as salt concentration increases . At typical salinity , it freezes at about − 2 ° C ( 28 ° F ) . The coldest seawater ever recorded ( in a liquid state ) was in 2010 , in a stream under an Antarctic glacier , and measured − 2.6 ° C ( 27.3 ° F ) . Seawater pH is typically limited to a range between 7.5 and 8.4 . However , there is no universally accepted reference pH - scale for seawater and the difference between measurements based on different reference scales may be up to 0.14 units . </P>
what is the percentage of salt in the ocean
what is the percentage of salt in the ocean
3.5 %
3.5 %