600 MAN IS MASTERING HIS MATERIAL WORLD 4. What is the displacement series? 5. Why is the displacement series sometimes called the electrochemical, or electromotive, series? 6. Explain in terms of the theory of atomic structure why carbon is such a good reducing agent. 7. Explain in terms of the theory of atomic structure why sodium is a more powerful reducing agent than carbon. 8. Explain the polarization of a cell. 9. Explain the action of the ordinary dry cell. 10. Explain what takes place when a lead storage battery is charged and discharged. n. Define oxidation in terms of oxygen, hydrogen, valence, and electrons. 12. What is the true nature of all oxidation-reduction reactions?
UNIT VIII SECTION 7 ACIDS ARE PROTON-DONORS AND BASES ARE PROTON- ACCEPTORS In all the reactions studied up to this point the reactions were either of the double decomposition type, which simply involved the removing of ions from a solution, or of the electron transfer type. This Section will describe two types of compounds, acids and bases, which will enter into double decomposition reactions and electron transfer reactions, but which are fundamentally different from all other compounds in that they lose and gain protons. Acids Owe Their Properties to Hydronium Ions. Before the discovery of the electrical nature of matter, the class of substances known as acids was recognized by the properties common to all acids. Thus an acid is a substance whose water solution (1) has a sour taste, (2) changes certain substances called indicators to develop a color different from that shown with bases, (3) neutralizes bases (i.e., reacts with bases in such a way that the properties of both the acid and base disappear) , series to produce hydrogen gas. (4) reacts with metals above hydrogen in the displacement It has been noted that hydrogen is the one substance that is common to all acids, so it is only natural to attribute the acid properties to hydrogen. Acids are familiar in everyday life. Citrus fruits taste sour because of the presence of citric acid in these fruits; tartaric acid imparts tartness to grapes; acetic acid is the acid in vinegar; muriatic acid (hydrochloric acid) is used to clean metal surfaces for soldering and to dissolve cement and mortar spots on brick and tile; hydrochloric acid is present in the gastric juice and accounts for the sour taste of regurgitated stomach contents; oxalic acid dissolves iron rust stains in clothes. According to the theory of ionization, an acid is a solution containing hydronium ions.^ The hydrogen compounds which react with water to ' The properties of acids were formerly ascribed to the presence of hydrogen ions (protons, H"*") in their solutions. The modern theory presented in this text differs from the above theory in that it ascribes the properties of acids to hydronium ions, which, as already pointed out, are considered to be formed by the combining of hydrogen ions with water molecules. 601