The Investigation of Protolytic Equilibria in Aqueous Solution

  • R. P. Bell

Abstract

Since the free proton is never encountered in solution, the equation A ⇌ B + H+, defining an acid-base pair, does not represent a realizable equilibrium, and all actual acid-base equilibria are of the form, A1 + B2 ⇌ B1 + A2. This type of reaction is known as a protolytic or proton-transfer reaction. Any qualitatively sensible concept of acid-base strength would imply that the equilibrium conversion of A1 + B2 into B1 + A2 will be more complete the stronger the acid A1 and the base B2 and the weaker the acid A2 and the base B1. Quantitatively, the equilibrium constant [B1][A2]/[A1][B2] is equal to the ratio of the (hypothetical) constants [B1][H+]/[A1] and [B2][H+]/[A2], and it will therefore measure the ratio of the acid strengths of A1 and A2, or the ratio of the base strengths of B2 and B1. Since these two ratios are equal, there is no point in considering the acid and base strengths separately, and it has become usual to describe the properties of any acid-base pair A−B in terms of the acid strength of A. Thus for the pair CH3COOH-CH3COO we speak of the acid strength of acetic acid rather than the base strength of acetate ion, and for the pair NH 4 + -NH3 of the acid strength of the ammonium ion rather than the base strength of ammonia.

Keywords

Acidity Barium Sodium Hydroxide Aniline Indole 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. 1.
    For a general account, see A. Albert and E. P. Serjeant, Ionization Constants of Acids and Bases, 2nd edn., Chapman and Hall, London, 1971.Google Scholar
  2. 2.
    O. Redlich and G. C. Hood, Disc. Faraday Soc., 24, 87 (1957); cf. T. F. Young, L. F. Maranville, and H. M. Smith, in The Structure of Electrolytic Solutions (ed. W. J. Hamer ), Wiley, New York, 1959, p. 35.Google Scholar
  3. 3.
    G. C. Hood, O. Redlich, and C. A. Reilly, J. Chem. Phys., 22, 2067 (1954); G. C. Hood and C. A. Reilly, J. Chem. Phys., 32, 127 (1960).Google Scholar
  4. 4.
    K. Heinziger and R. E. Weston, J. Chem. Phys., 42, 272 (1965).CrossRefGoogle Scholar
  5. 5.
    A. K. Covington, M. J. Tait, and Lord Wynne-Jones, Proc. Roy. Soc., A, 286, 235 (1965).CrossRefGoogle Scholar
  6. 6.
    R. W. Duerst, J. Chem. Phys., 48, 2275 (1968).CrossRefGoogle Scholar
  7. 7.
    J. H. R. Clarke and L. A. Woodward, Trans. Faraday Soc., 62, 2226 (1966).CrossRefGoogle Scholar
  8. 8A.
    K. Covington and T. H. Lilley, Trans. Faraday Soc., 63, 1749 (1967).CrossRefGoogle Scholar
  9. 9.
    K. N. Bascombe and R. P. Bell, J. Chem. Soc., 1096 (1959).Google Scholar
  10. 10.
    E. Högfeldt, J. Inorg. Nucl. Chem., 17, 302 (1961).CrossRefGoogle Scholar
  11. 11.
    A. K. Covington, J. G. Freeman, and T. H. Lilley, J. Phys. Chem., 74, 3773 (1970).CrossRefGoogle Scholar
  12. 12.
    E. Grunwald and J. F. Haley, J. Phys. Chem., 72, 1944 (1968).CrossRefGoogle Scholar
  13. 13.
    See, e.g., F. S. Feates and D. J. G. Ives, J. Chem. Soc., 2798 (1956); F. S. Feates, D. J. G. Ives, and J. H. Pryor, J. Electrochem. Soc., 103, 580 (1956); D. J. G. Ives and P. D. Marsden, J. Chem. Soc., 649 (1965).Google Scholar
  14. 14.
    P. Ballinger and F. A. Long, J. Am. Chem. Soc., 81, 2347 (1959); R. P. Bell and D. P. Onwood, Trans: Faraday Soc., 58, 1557 (1962).Google Scholar
  15. 15.
    See, e.g., R. J. L. Andon, J. D. Cox, and E. F. G. Herington, Trans. Faraday Soc. 50, 918 (1954); R. A. Robinson, in The Structure of Electrolytic Solutions (ed. W. J. Hamer), Wiley, New York, 1959, p. 253. A general account of this method is given in Ref. 1.Google Scholar
  16. 16.
    J. F. Bunnett and F. P. Olsen, Canad. J. Chem., 44, 1899 (1966).CrossRefGoogle Scholar
  17. 17.
    M. J. Jorgenson and D. R. Hartter, J. Am. Chem. Soc.,85, 878 (1963): C. D. Johnson, A. R. Katritzky, and S. A. Shapiro, J. Am. Chem. Soc.,91, 6654 (1969): P. Tickle, A. G. Briggs, and J. M. Wilson, J. Chem. Soc.,B, 65 (1970). The last two references give values from 15°C to 90°C.Google Scholar
  18. 18.
    K. Bowden, Chem. Rev., 66, 119 (1966); C. H. Rochester, Chem. Soc. Quart. Rev., 20, 511 (1966).Google Scholar
  19. 19.
    G. Yagil, J. Phys. Chem., 71, 1034 (1967).CrossRefGoogle Scholar
  20. 20.
    K. Bowden and R. Stewart, Tetrahedron, 21, 261 (1965).CrossRefGoogle Scholar
  21. 21.
    T. S. Moore and T. F. Winmill, J. Chem. Soc., 91, 1373 (1907); 101, 1635 (1912).Google Scholar
  22. 22.
    E.g., N. V. Sidgwick, Chemical Elements and Their Compounds, Oxford, 1950, 659.Google Scholar
  23. 23.
    I. B. Khakham, Zh. Obshch. Khim., 18, 1215 (1948): Chem. Abs., 43, 6891 (1949).Google Scholar
  24. 24.
    L. D. Elliott, J. Phys. Chem., 28, 887 (1924); I. L. Clifford and E. Hunter, J. Phys. Chem., 37, 101 (1933).Google Scholar
  25. 25.
    D. L. Hildenbrand and W. F. Giauque, J. Am. Chem. Soc., 75, 2811 (1953).CrossRefGoogle Scholar
  26. 26.
    R. D. Waldron and D. F. Hornig, J. Am. Chem. Soc., 75, 6079 (1953).CrossRefGoogle Scholar
  27. 27.
    B. P. Rao, Proc. Indian Acad. Sci., 20A, 292 (1944).Google Scholar
  28. 28.
    See, e.g., P. F. van Velden and J. A. Ketelaar, Chem. Weekblad, 43, 401 (1947).Google Scholar
  29. 29.
    J. L. Copp and D. H. Everett, Disc. Faraday Soc., 15, 174 (1953).CrossRefGoogle Scholar
  30. 30.
    H. S. Gutowsky and S. Fujiwara, J. Chem. Phys., 22, 1782 (1954).CrossRefGoogle Scholar
  31. 31.
    J W. McBain, J. Chem. Soc., 101, 814 (1912); D. Vorländer and S. Strube, Ber., 46, 172 (1913).Google Scholar
  32. 32.
    A. Thiel, Ber., 46, 241 (1912).Google Scholar
  33. 33.
    C. Faurholt, J. Chim. Phys., 21, 400 (1924); 22, 1 (1925).Google Scholar
  34. 34.
    F. J. W. Roughton, J. Am. Chem. Soc., 63, 2930 (1941).CrossRefGoogle Scholar
  35. 35.
    J. Meier and G. Schwarzenbach Hely. Chim. Acta, 40, 907 (1957).CrossRefGoogle Scholar
  36. 36.
    G. A. Mills and H. C. Urey, J. Am. Chem. Soc., 62, 1019 (1940).CrossRefGoogle Scholar
  37. 37.
    D. Berg and A. Patterson, J. Am. Chem. Soc., 75, 5797 (1953); K. F. Wissbrunn, D. M. French, and A. Patterson, J. Phys. Chem., 58, 693 (1954).Google Scholar
  38. 38.
    G. Schwarzenbach and E. Felder, Heiy. Chim. Acta, 27, 1701 (1944).CrossRefGoogle Scholar
  39. 39.
    D. Turnbull and S. H. Maron, J. Am. Chem. Soc., 65, 212 (1943).CrossRefGoogle Scholar
  40. 40.
    T. C. Waddington, Trans. Faraday Soc., 54, 25 (1958).CrossRefGoogle Scholar
  41. 41.
    P. R. Patel, E. C. Moreno, and J. M. Patel, J. Res. Nat. Bur. Stand., A, 75, 205 (1971).Google Scholar
  42. 42.
    See, however, E. Wiberg, Z. Phys. Chem., 171A, 1 (1934).Google Scholar

Copyright information

© R. P. Bell 1973

Authors and Affiliations

  • R. P. Bell
    • 1
  1. 1.University of StirlingScotland

Personalised recommendations