Activity and the Systematic Treatment of Equilibrium

Ionic and hydrated radii o several ions. Smaller, more highly charged ions bind water molecules more tightly and behave as larger hydrated species.3 

Ions and molecules in solution are surrounded by an organized sheath of solvent molecules. The oxygen atom of H20 has a partial negative charge and each hydrogen atom has half as much positive charge. 

Water binds to cations through the oxygen atom. The first coordination sphere of Li4, for example, is composed of 4 H,0 molecules.1 Cl binds 6 H20 molecules through hydrogen atoms.1-2 H20 exchanges rapidly between bulk solvent and ion-coordination sites. 

Ionic radii in the figure are measured by X-ray diffraction of ions in crystals. Hydrated radii are estimated from diffusion coefficients of ions in solution and from the mobilities of aqueous ions in an electric field.3-4 Smaller, more highly charged ions bind more water molecules and behave as larger species in solution. The activity of aqueous ions, which we study in this chapter, is related to the size of the hydrated species. 

Consider a saturated solution of CaS04 in distilled water. 

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Two chapters on activity coefficients and the systematic treatment of equilibrium from the sixth edition were condensed into Chapter 8. A new, advanced treatment of equilibrium appears in Chapter 13. This chapter, which requires spreadsheets, is going to be skipped in introductory courses but should be of value for advanced undergraduate or graduate work. New topics in the rest of this book include the acidity of metal ions in Chapter 6, a revised discussion of ion sizes and an example of experimental design in Chapter 8. pH of zero charge for colloids... 

SH Considering just acid-base chemistry, not ion pairing and not activity coefficients, use the systematic treatment of equilibrium to find the pH and concentrations of species in 1.00 L of solution containing 0.100 mol ethylenediamine and 0.035 mol HBr. Compare the pH with that found by the methods of Chapter 11. 

HH A solution containing 0.008 695 m KH2P04 and 0.030 43 m Na2HP04 is a primary standard buffer with a stated pH of 7.413 at 25°C. Calculate the pH of this solution by using the systematic treatment of equilibrium with activity coefficients from... 

The quantitative evaluation of the systematic relations that determine equilibrium concentrations (or activities) of a solution constitutes a purely mathematical problem, which is amenable to exact and systematic treatment. 

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