Comments re Chapter 11 Problems:

11-2

Another T/F exercise.

11-4

(Not a short problem, but very important).
All parts require solving an equilibrium problem for a reaction involving ions. Solutions containing ions are not ideal; activity coefficients for uncharged molecules are usually assumed to be 1, but activity coefficients for ions must be determined experimentally or estimated using an equation like the Davies equation.
(a) Dissociation of formic acid in pure water.
(b) Dissociation of formic acid in a solution containing an electrolyte that changes the ionic strength but that does not participate in the chemical reaction being considered.
(c) Dissociation of formic acid in a solution that also contains the formate ion, which (along with the accompanying Na+ ion) changes the ionic strength, and which also participates in the chemical reaction being considered (common ion effect). Note that this third solution is a buffer because the concentrations of the formic acid (undissociated acid) and formate ion (conjugate base) are similar.

11-6

Exercise in calculating ionization constants from data in thermodynamic tables. Note that very small and very large equilibrium constants are seldom known very well.

11-8

A quick calculation to show that the pH of a NaCl(aq) solution is not 7.00, even if the temperature is 298 K. Neither the Na+(aq) ion nor the Cl-(aq) undergoes hydrolysis, but they change the ionic strength, which lowers the activity of the H+(aq) and OH-(aq) ions and so increases their concentrations.

11-9

It is important to remember that Kw changes with temperature; the only temperature at which the value is 1.0 x 10-14 is 298 K.
(a) Use an empirical expression to get Kw at normal body temperature.
(b) Estimate Kw at normal body temperature by using the expression for the temperature dependence of ln K.

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