The Extraordinary Properties Of Ordinary Solutions

Yu.Ya.Fialkov Mir Publishers Moscow THE EXTRAORDINARY PROPERTIES OF ORDINARY SOLUTIONS KD. fl. OnanKOB HEOBbNHblE CBOMCTBA OBbNHblX PACTBOPOB l/l3flaTenbCTBO «fleflarorMKa» Scientists to Schoolchildren Yu.Ya. Fiaikov THE EXTRAORDINARY PROPERTIES OF ORDINARY SOLUTIONS Translated from the Russian by Boris V. Kuznetsov MIR PUBLISHERS MOSCOW First published 1985 Revised from the 1978 Russian edition Ha anzAuiicKOM H3bixe © HsaaTejibCTBO «ne;iaroiHKa» 1978 © English translation, Mir Publishers, 1985 Contents On Dry Lemonade and About This Book 6 What is a Solution? 9 Midway Between Gases and Crystalline Solids 10 Water - Puzzling and Extraordinary 18 From the Physicist's Point of View 32 Those Dissociating into Ions 49 Acids and Bases-is This Simple as That? gQ Ions in Solutions 69 Flow of Current Through a Solution 77 Solubility 90 "Not in Water Alone" 93 Is There Life Outside Earth? 97 On Dry Lemonade and About This Book It is a hot July day. Feeling thirsty, you look around for a nearby soda fountain and find none. But your eyes catch the sign at the top of a kiosk. Styled in fanciful Old-Slavic letters, it promises Russian kvas, a soft drink perhaps as popular with Russians as Coca-Cola with Americans. No, there is not a drop of kvas left, the girl behind the counter says. Nor a bottle of Buratino (another Russian favourite). What she can offer is lemonade. Hopefully, I opt for two. The girl holds o u t - n o , not the familiar paper cups full of the bubbling liquid. In her hand are two small white packages stuffed with a crackling powder. That is dry lemonade. Well, your thirst has to wait until you are back home. But that is a good point from which to start with a book about solutions-this book. Of course, it would be more appropriate to begin by stating that the subject of solutions is extremely important, more important than anything else. For solutions are everywhere around us. Tea is a solution. A perfume is a solution. A sea wave is a solution. The pickle for cucumbers is a solution. Even cucumbers themselves are solutions. But it is not enough just to declare that solutions are vitally important. This must be proved. And this is the object of the book you are going to read. Deep in thought about the solutions so amazingly present everywhere, you get back home, take a package of dry lemonade and, following the simple instructions stamped on it, empty its contents in a glass and fill it with tap water. In an instant, the powder dissolves, and gas bubbles stream violently to the surface. You take a sip and feel satisfied - the drink is sweet and, most important, full of fizz. 6 Of course, the fizz, or gas, that goes up as bubbles in the do-it-yourself lemonade is not stored in the package. It comes from a chemical reaction. The point is that the powder contains (in addition to sugar) baking soda and citric acid. The two eagerly react with each other to form the sodium salt of citric acid and gaseous carbon dioxide. Simple as that, and no tricks. Simple? No tricks? Why is it then, you may ask, that the soda and the acid do not react when the powder is dry? Why is it that the mixture has to be dissolved for the reaction to take place? The answer is, Corpora non agunt soluta, which is the Latin for "Bodies (substances) do not react unless dissolved". Alchemists discovered this rule many centuries ago. We take it for granted that chemical reactions take place in solutions, but hold this fact at the back of our minds or even completely forget about it. To prove the point, I challenge you to take what might pass for a psychologic