A chemistry team measures the molar conductivity (Λm) at infinite dilution for 0.050M solutions of three hypohalous acids at 25∘C. The data are summarized below.
Acid
Λm (S cm2 mol−1)
HOCl
1.5×10−2
HOBr
7.2×10−3
HOI
2.8×10−3
Assume that the contribution of undissociated acid molecules to conductivity is negligible and that each dissociation event produces one H+ and one conjugate-base ion.
Respond to the following prompts.
(a) Rank the three acids in order of increasing Ka value. Justify your ranking using the data provided.
(b) Derive an expression that relates Λm to the degree of ionization (α) of a monoprotic acid in dilute solution. State any assumptions made.
(c) Using your expression from part (b), calculate the numerical value of Ka for each acid. Clearly outline each calculation step.
(d) Discuss how the calculated Ka values correlate with periodic properties of the central halogen atom, and predict qualitatively where the hypothetical acid HOAt (ataiatic acid) would fall in the ranking.