University Chemistry ›› 2021, Vol. 36 ›› Issue (8): 2009043.

• Between Teacher and Student •

### Multi-Equilibrium Calculations for HF Solution and HF-F- Solution

Ying Zhang, Xinjun Quan()

• Received:2020-09-18 Accepted:2021-01-18 Published:2021-01-25
• Contact: Xinjun Quan E-mail:quanxj@jlu.edu.cn

Abstract:

In HF solution and HF-F- solution, there are not only the dissociations of hydrofluoric acid but also the reactions between hydrogen fluoride and fluoride ion, so the equilibrium concentration of each component is the final product of two equilibria. Theoretically, the correct result can be obtained only if the two equilibria are considered simultaneously. However, much attention has been paid to the dissociation equilibrium of HF than to the HF-F- association in teaching, as a result students are used to take the wrong calculation method when confronting such problems. In order to develop students' comprehensive abilities to deal with the calculations of complex systems, the simple and accurate formulas for calculating the ion concentrations in HF solution and HF-F- solution are derived based on multi-equilibrium. By comparison, it is found that both equilibria must be considered in all cases, except that the concentration of HF solution is less than 1.91×10-2 mol·L-1 which can be approximately calculated as monobasic weak acid.

MSC2000:

• G64