The Future is Forming

Salinity is a measure of the total amount of dissolved solids present in water.

• The salinity of fresh water is less than 0.05% by weight.
• The salinity of ocean water typically ranges from about 3.3% to 3.7% (3.3 to 3.7 parts per hundred) by weight.
• Marine geologists normally use units of parts per thousand (abbreviated as ‰), so the salinity of ocean water is about 35‰, compared to less than 0.5‰ for fresh water.
• Units of parts per million are sometimes used: the salinity of ocean water is about 35,000 ppm, while the salinity of fresh water is typically less than 500 ppm.

As determined initially by Dittmar in 1884 on samples collected during the Challenger Expedition (1872-1876), the ratios of the various ions in sea water are nearly independent of salinity and location in the ocean.

• The Red Sea, for example, with a salinity of close to 40‰, has more ions than “average” seawater. However, here and elsewhere around the world, the relative proportions of all ions are the same. Worldwide, the ratio of chloride ions to sodium ions in seawater is 55.1 / 30.6 = 1.8.
• The “Rule of Constant Proportions” applies only to seawater and not fresh water (i.e., river water). Note the magnitude of the ionic concentrations in fresh water – a slight change of a few parts per million either higher or lower will significantly change the ratios.

The ionic concentrations in this table are approximations compiled from numerous literature sources. The specific values in your particular sample may be different from what is shown, but in the case of seawater, the ratios of the ions will be the same.

Posted by Engineering Quality Solutions on Thursday, July 09, 2009 at 11:12 AM | Permalink |