Acid-base and oxidation-reduction balances

The Acid-Base and Oxidation-Reduction Balances of the Earth... 

Chapter 16 considers a broad but closely related set of chemical processes that control the acid-base and oxidation-reduction (or redox) balances of the planet. It will be seen that both sets of processes depend greatly on... 

Ascorbate and Oxidation-Reduction Potential. The ascorbic acld-dehydroascorbic acid system is believed to play an important part in maintaining optimum oxidation-reduction conditions in the tissues. The oxidation-reduction potential, like acid-base balance and pH, must be balanced within fairly narrow limits for normal health. Any disturbance of oxidation-reduction potential, such as would result from depletion of ascorbate reserves in cancer, could have deleterious systemic effects (3). 

Net ionic equations are used in discussions of limiting quantities problems (Chapter 10), molarities of ions (Chapter 11), balancing oxidation-reduction equations (Chapter 16), acid-base theory (Chapter 19), and many other areas beyond the scope of this book. They make possible writing equations for halfreactions at the electrodes in electrochemical experiments (Chapter 17), which have electrons included explicitly in them. They make understandable the heat effects of many reactions such as those of strong acids with strong bases. 

Net ionic equations are used extensively in chemistry. For example, equilibrium expressions for acid-base reactions, as well as for the ionization of water itself, are conventionally written in the form of net ionic equations. Many complex oxidation-reduction equations are balanced using net ionic equations. These topics are introduced in Chapters 16 and 19. 

In oxidation-reduction reactions, electron transfers (e ) are coupled with the transfer of protons (H ) to maintain a charge balance. A modification of the redox balance corresponds to a modification of the acid-base balance. The net reactions of the oxidation of C, S, and N exceed reduction reactions in these elemental cycles. A net production of ions in atmospheric precipitation is a necessary consequence. The disturbance is transferred to the terrestrial and aquatic environments, and it can impair terrestrial and aquatic ecosystems. 

Inorganic chemistry may be divided into four types of reaction acid/base, precipitation, complexation and redox. It is when considering redox reactions that oxidation numbers are used to greatest advantage. This is particularly true when ensuring that a reaction equation has been properly balanced, i.e. that the same amount of reduction as oxidation has taken place. 

In an oversimplified way, it may be stated that acids of the volcanoes have reacted with the bases of the rocks the compositions of the ocean (which is at the fkst end pokit (pH = 8) of the titration of a strong acid with a carbonate) and the atmosphere (which with its 2 = 10 atm atm is nearly ki equdibrium with the ocean) reflect the proton balance of reaction 1. Oxidation and reduction are accompanied by proton release and proton consumption, respectively. In order to maintain charge balance, the production of electrons, e, must eventually be balanced by the production of. The redox potential of the steady-state system is given by the partial pressure of oxygen (0.2 atm). Furthermore, the dissolution of rocks and the precipitation of minerals are accompanied by consumption and release, respectively. 

As you know, when an atom loses electrons, its oxidation number increases when an atom gains electrons, its oxidation number decreases. Therefore, the total increase in oxidation numbers (oxidation) must equal the total decrease in oxidation numbers (reduction) of the atoms involved in the reaction. The balancing technique called the oxidation-number method is based on these principles. The CHEMLAB at the end of this chapter gives you the opportunity to perform and balance the copper-nitric acid redox reaction. 

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