By Jonny Lupsha, Wondrium Staff Writer
World Cup host Qatar uses desalination to make seawater drinkable. Qatar is one of the most water-stressed countries on Earth. Seawater is full of dissolved chemicals.
The 2022 World Cup will turn the world’s focus to the Persian Gulf nation of Qatar, which has no natural rivers and very little rainfall. Qatar instead depends on the expensive process of desalination, which makes seawater drinkable, in order to provide its citizens with potable water. Desalination burns a high amount of fossil fuels to separate the salt and other chemical components from seawater.
Ocean water is full of sodium ions, which give it its salty taste and make it very unwise to drink. In his video series Oceanography: Exploring Earth’s Final Wilderness, Dr. Harold J. Tobin, Professor in the Department of Earth and Space Sciences at the University of Washington in Seattle, breaks down the contents and chemistry of seawater.
Water, Water Everywhere …
“Seawater is not just water; it’s water with a lot of stuff dissolved in it,” Dr. Tobin said. “The solvent is the medium in which the substances are dissolved. The solute is that which is dissolved, so the sodium and chloride ions and other ions that are dissolved in the water […] such as a salt crystal gets dissolved in the water by a separation of the negatively and positively charged ions.”
Salt crystals can be thought of as many chloride ions and sodium ions stuck together by hydrogen bonding. Water has a charge imbalance and pulls the ions off of the salt crystal. Chloride ions stick to the positively charged side of the water molecules, while sodium ions stick to the negatively charged side. Water is considered a universal solvent because of its charge imbalance.
So what is seawater, really?
“It is nothing more than pure water, H2O, with a small amount of dissolved salts and then […] many other different elements and compounds in small quantities,” Dr. Tobin said. “We use the term salinity to mean the total quantity of these dissolved inorganic solids, so it’s not just the amount of sodium chloride, for example, or potassium chloride or some other individual salt.
“It’s the total quantity of all the inorganic matter that’s dissolved in the water, measured by weight.”
Principle of Constant Proportions
The most abundant compounds in ocean water are sodium ions and chloride ions, which we think of as ordinary table salt. Every kilogram of ocean water has approximately 35 grams of salinity in it, or 3.5%. There are also trace amounts of sulfates, magnesium, bicarbonate, calcium, and potassium in seawater.
“The ocean, then, contains about 3.5% salt—not very much,” Dr. Tobin said. “It’s mostly water, but that still amounts for the entire ocean of the planet to 5.5 trillion tons of salt out there dissolved in the ocean,” Dr. Tobin said. “There are also a bunch of more minor and more trace constituents of seawater. Some of the key ones are nitrogen, iron, and phosphorus, which, as you know if you’re a gardener at all, are all important nutrients that potentially are limiting factors for the growth of organisms.”
Amazingly enough, these proportions of solutes in seawater are the same for all ocean water around the globe. From the Mediterranean to the North Atlantic and down near Antarctica, the same byproducts of this water are found in the same amounts. It’s known as the principle of constant proportions or Forchheimer’s principle.
Separating the water from the solutes is another matter entirely.
Oceanography: Exploring Earth’s Final Wilderness is now available to stream on Wondrium.