Page 7 - Curriculum Visions Dynamic Book

(Below) The substances dissolved in water are clear to see in dried-out lake beds such as this one in a desert region of California.
forms into droplets (which make clouds), it has already attracted gases from the
air and has become weakly acidic. Water droplets form around specks of dust in the air. Many such specks are made of salt, which are then dissolved in the water.
The water that contains the greatest impurities is the ocean and some water
in rocks (known as groundwater). That
is because water reacts with many rocks, and some of the products of the reactions remain dissolved in the water.
Water moving through the ground
is always in contact with rocks, and so
it can dissolve considerable quantities of minerals. Indeed, this kind of water is often valued for its impurities. It is called “mineral water” and is believed by some to have health-giving properties. The sea contains salts that have been dissolved in
rocks and carried by rivers. When the water evaporates to form more water vapour and so continue the water cycle, it leaves behind its impurities, leading to “salty” water, although salt (sodium chloride) is not the only substance dissolved in seawater.
Water is also an excellent catalyst for many chemical reactions, and it can act
either as an oxidizing agent or as a reducing agent. For example, water can oxidise carbon to carbon monoxide, liberating hydrogen gas. It can also reduce chlorine gas to hydrogen chloride, releasing oxygen gas.
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