Salts from the sea – Sea-water is a mixture of various salts such as magnesium, potassium metals, calcium, and sodium.

In fact, sea-water contains about 3.6 percent by mass of dissolved salts which include the following salts

• Sodium chloride (Common salt) – 2.8 percent
• Magnesium salts – 0.6 percent
• Potassium salts – 0.1 percent
• Calcium salts – 0.1 percent

Thus, the most abundant salt present in the sea-water is sodium chloride (common salt).

Preparation of Common Salt from Sea-Water – Common salt is the most abundant salt is present in the sea-water. Therefore, sodium salt (common salt) is prepared commercially from sea-water.  The common salt is prepared from sea-water as follows

Sea-water is collected in small lagoons (shallow lakes) on the shores of the sea in coastal areas. This sea-water is then allowed to evaporate by the heat of the sun. After that, all the sea-water is collected in the lagoon has evaporated, the white crystals of common salt or (sodium chloride) are left behind. The common salt (sodium chloride) is prepared in this way is purified by the process of recrystallization.

Why Common Salt is Iodized – The common salt containing some iodine such as potassium iodide or potassium iodate is known as ‘’iodized common salt’’. When the common salt is obtained from the sea-water is iodized, then the amount of iodine present in it increases. The common salt is iodized to prevent the disease is called ‘’goitre’’ in human beings that occurs due to the deficiency of iodine in the human body.

How Sea-Water gets its Salts – The sea-water gets its salts from the rivers that flow into it. It can be explained as below –

During the weathering (breaking) of land rocks and the erosion of soil by water, the salts present in them keep on dissolving in water. These dissolved salts mix in rainwater and go into the rivers. When these rivers meet the sea, then the salts are present in them reach the sea-water. Some of the salts are present in the sea-water precipitate and settle down on the sea-bed in the form of sediments. Some of the salts present in the sea-water are also used by the plants and animals that are found in the sea to build shells.

For example, seashells and pearls are made up of calcium carbonate salt which is present in the sea-water. The loss of salts from sea-water which takes place due to sedimentation and withdrawal by plants and animals is compensated by the arrival of fresh salts with the river water. In this way, the overall concentration of salts in the sea-water that remains fairly constant.