Rank the following acids in order of increasing equivalence point pH if titrated with NaOH.

Question

For the following scenarios, consider that you have equal volumes and concentrations of the acids in Part 1, and that you have equal volumes and concentrations of the bases in Part 2.

A. Rank the following acids in order of increasing equivalence point pH if titrated with NaOH.

HCOOH HCl CH₃COOH HNO₂ HClO₂ HBrO

B. Rank the following bases in order of increasing equivalence point pH if titrated with HCl.

NaF LiOH NH₃ NaOCl CH₃NH₂

Answer 1

A. NaOH is a strong base, so the following will apply:

titration of HCOOH (a weak acid), pH will be >7 @ equivalence

titration of HCl (a strong acid), pH will be = 7 @ equivalence

titration of HNO2 (a weak acid), pH will be >7 @ equivalence

titration of HClO2 (a weak acid), pH will be >7 @ equivalence

titration of HBrO (a weak acid), pH will be >7 @ equivalence

To rank them, one needs to compare the Ka values of the various weak acids. Since they are not provided, we cannot complete the answer, other than to say that HCl would be the lowest pH @ equivalence.

B. HCl is a strong acid, so the following will apply:

NaF + HCl ==> NaCl + HF pH will be <7 as HCl is stronger than HF

LiOH is a strong base so pH @ equivalence will be = 7

NH3 is a weak base, so pH @ equivalence will be <7

NaOCl + 2HCl ==> NaCl, + H₂O + Cl₂ pH depends on temp. but should be <7

CH3NH2 is a weak base, so pH @ equivalence will be <7

Again, as above, to rank them, one needs additional information about Kb values.