Describe clearly how the activity coefficient of an ion, i, depends on its charg
ID: 501044 • Letter: D
Question
Describe clearly how the activity coefficient of an ion, i, depends on its charge, the effective size and the ionic environment. How would you expect the solubility of the following compounds to vary in a series of solutions of increasing ionic strength generated by adding KNO_3. ammonia ammonium chloride If the ionic strength was increased by adding KCl, the solubility of which one of the above two solutes be affected significantly and why. What assumption(s) must be made to derive the Henderson Hasselbach equation in its normal form? pH = pK_a + log [A^-]/[HA] "It could be argued that a compound like the one shown on the right may be used as a pH buffering material in aqueous solutions, by itself". What would that argument be? However the compound shown above cannot be used as a buffer by itself. As a matter of fact it would be a very poor buffer. What is the flaw in the "argument" made in question 1(f)?Explanation / Answer
b. Ionic coefficient depends upon size of the ion, as the size goes up, the ionization strength of ion goes down. Charge directly depends on the ionic coefficient, with increasing charge the coefficicient also increases. With more ionizing environment, the possibility of a salt to present in ionic form raher than a pure compound increases and thus ionic coefficient also increases.
c. The solubility of species upon addition of KNO3
(i) ammonia increases upon addition of KNO3 due to the formation of NH4NO3 in solution.
(ii) ammonium chloride ionic strength and solubility stays the same.
d. When ionic strength was increased by adding KCl, the solubility of ammonia would be increased singnificantly in solution.
e. The Hendersen-Hasselbalck equation as written below describes the relation between weak acid/conjugate base or weak base/conjugate acid in solution. The assumption made here is the concentrations at equilibrium of acid and base component in solution remains the same and not changed.
f. Looking at the structure on the right, the compound and it conjugate base may act as a buffer in solution. It reacts with added base or acid,
g. The compound may act as buffer when treated with HCl to form conjugate acid of th base shown above.
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