Page 45 - Curriculum Visions Dynamic Book

100cm3 of distilled water at 25°C.The masses of each of the solids shown here will dissolve in this volume of water to make a saturated solution.
Potassium permanganate (potassium manganate(vii), KMnO4), 32.0 g
Sodium thiosulfate (Na2S2O3), 302.0 g
Iron(iii) chloride (FeCl2), 196.0 g
Potassium perchlorate (potassium chlorate(vi), KClO4), 6.5 g
Potassium dichromate(vi) (K2Cr2O7), 37.0 g
Calcium hydroxide (Ca(OH)2), 0.1 g
How hydrophilic substances dissolve
Not all substances that dissolve in water are like salt (that is, they are not made up of ionic particles that can be split apart). Alcohol (as found in alcoholic beverages, and whose scientific name is ethanol) dissolves readily in water. Most of an alcoholic drink is, in fact, water. In this case the alcohol molecules are similar to water molecules (although much more complicated) and so can attract water molecules as well as attracting themselves.
Why hydrophobic substances do not dissolve
Why will water not dissolve everything? The answer to this is that “like dissolves like.” The substance dissolving in water has to have something in common with water in the way it is made. Fat is unlike
water in its structure and behavior, and so it does
How much will dissolve?
Throughout this book you have seen how water easily dissolves other substances. But how much can be dissolved? Is it the same for every substance? To find out, it is possible to add more and more of
a chemical to water until no more will dissolve. You know no more will dissolve because no matter how much the solution is stirred, some solid remains at the bottom.
Different substances have widely varying solubilities.
The temperature of the solution also has an important effect on the amount of a substance that will dissolve. In general, substances become much more soluble as the temperature is raised.
45