Tham khảo sách 'chemistry part 27, julia burdge,2e (2009)', khoa học tự nhiên, vật lý phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 656 CHAPTER 16 Acids and Bases As for any chemical equations we can add these two equilibria and cancel identical terms H2O Z OFT a The sum is the autoionization of water. In fact this is the case for any weak acid and its conjugate base or for any weak base and its conjugate acid. Remember that the hydronium ion can be expressed as either H or H3O . These are two equivalent ways to represent the autoionization of water. Recall that when we add two equilibria the equilibrium constant for the net reaction is the product of the equilibrium constants for the individual equations M Section . Thus for any conjugate acid-base pair Equation Equation gives the quantitative basis for the reciprocal relationship between the strength of an acid and that of its conjugate base or between the strength of a base and that of its conjugate acid . Because Kw is a constant Kb must decrease if Ka increases and vice versa. Sample Problem shows how to determine ionization constants for conjugates. Think About It Because the conjugates of weak acids and bases have ionization constants salts containing these ions have an effect on the pH of a solution. In Section we will use the ionization constants of conjugate acids and conjugate bases to calculate pH for solutions containing dissolved salts. Determine a fb of the acetate ion CH3COO b Ka of the méthylammonium ion CH3NH3 c Kb of the fluoride ion F and d Ka of the ammonium ion NHJ . Strategy Each species listed is either a conjugate base or a conjugate acid. Determine the identity of the acid corresponding to each conjugate base and the identity of the base corresponding to each conjugate acid then consult Tables and for their ionization constants. Use the tabulated ionization constants and Equation to calculate each indicated K value. Setup a A Kb value is requested indicating that the acetate ion is a conjugate base. To identify the corresponding BrOnsted acid add a proton to the formula to get
