The Chemistry of Seawater
THE OCEANS CONTAIN MILLIONS OF DISSOLVED chemical substances. Most of these are present in exceedingly small concentrations.
Those present in significant concentrations include sea salt, which is not a single substance but a mixture of charged particles called ions.
Other constituents include gases such as oxygen and carbon dioxide.
One reason the oceans contain so many dissolved substances is that water is an excellent solvent.
The Salty Sea
The salt in the oceans exists in the form of charged particles, called ions, some positively charged and some negatively charged.
The most common of these are sodium and chloride ions, the components of ordinary table salt (sodium chloride). Together they make up about 85 percent by mass of all the salt in the sea. Nearly all the rest is made up of the next four most common ions, which are sulfate, magnesium, calcium, and potassium. All these ions, together with several others present in smaller quantities, exist throughout the oceans in fixed proportions.
Each is distributed extremely uniformly—this is in contrast to some other dissolved substances in seawater, which are unevenly distributed.
Sources and Sinks
The ions that make up the salt in the oceans have arrived there through various processes. Some were dissolved out of rocks on land by the action of rainwater and carried to the sea in rivers.
Others entered the sea in the emanations of hydrothermal vents (see p.188), in dust blown off the land, or came from volcanic ash. There are also “sinks” for every type of ion—processes that remove them from seawater. These range from salt spray onto land to the precipitation of various ions onto the seafloor as mineral deposits. Each type of ion has a characteristic residence time.
This is the time that an ion remains in seawater before it is removed. The common ions in seawater have long residence times, ranging from a few hundred years to hundreds of millions of years.
Distribution of chemicals
The above pie graph show the percentage of chemical presant in sea.
Now lest us see most common question asked by people on Google about this topic. People also ask
Ans. sodium chloride
There are several salts in seawater, but the most abundant is ordinary table salt or sodium chloride (NaCl).
2.What is the molarity of seawater?
Ans. With the unreasonable assumption that all 35.9 g are NaCl, we can divide by the molar mass of NaCl (58.44 g/mole) and find that the molarity of salt in seawater is about 0.61
3.Is sea water a compound or mixture?
Ans. Seawater is a mixture of many different substances. Some of these substances can be observed when the water in seawater evaporates and leaves behind salt. Water, H2O, is a pure substance, a compound made of hydrogen and oxygen.
Thank you
Source : internet & ocean book by dk
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