Page 43 - Curriculum Visions Dynamic Book

the molecules or ions scattered evenly among the molecules of the liquid it has dissolved in. We call a solution in water an aqueous solution (aqueous meaning “of water”).
Why water is not quite a
“universal solvent”
One of the most noticeable things about water is how well it can dissolve other substances and therefore how important it is to us and to all living things. That is why it has been called the “universal solvent.”
When you stir coffee and sugar into hot water, you produce a hot aqueous solution. The biggest aqueous solution on Earth is, of course, the world’s oceans, with their vast amount of dissolved salts. These salts are, by the way, one of the world’s greatest reservoirs of many chemical substances.
Water also forms the basis of all living things. It makes up 70% by weight of the human body. Water is able to transport substances in solution, both other liquids, such as foods and ions such as sodium and potassium, as well as gases, such as oxygen and carbon dioxide.
As we have seen earlier in this book, water is a polar solvent. As such, it has the special property of being able to dissolve many ionic solids such as sodium chloride – salt. This produces a solution in water.
Water makes ionic substances dissolve in the following way. When an ionic substance like salt (which is a chemical made of sodium and chlorine) is dissolved in water, the positive parts of the salt (the sodium ions) are attracted to the negative end of the water molecule, while the negative parts of the salts (the chlorine ions) are attracted to the positive parts of the water molecule. Because the parts of the salt are dragged to opposite parts of the water molecules, the salt splits apart and so dissolves.
(Below) When you stir coffee and sugar into hot water, you produce a hot aqueous solution.
43
Water
The coffee grains have dissolved to produce a coffee solution.
Instant coffee grain