Common ion effect: pH changes when adding LiF to HF, KI to HI, and NH4Cl to NH3

[tribalman100]

Homework Statement

does the ph increase , decrease or remain the same on addition of each of the folling
a) LiF to an HF Solution
B) KI to an HI solution
C) NH4Cl to an NH3 solution

Homework Equations

The Attempt at a Solution

i got the equations and the answers to these i just want to know the reason so i can do it next time on why Lif ph increases, Ki's remains the same and that NH4Cl's decreases . it would be a great help and this explanation might save my chemistry grade. thanks for the help guys

 

[Kushal]

well, think in terms of equillibria.

HF <------> H+ + F-
LiF <------> Li+ + F-

when you add LiF, the total concentration of F- increases in solution. the dynamic equilibirum of HF is disturbed. according to LCP the backward reaction is momentarily favoured to decrease F- concentration. at the same time, the concentration of H+ also decreases. hence the pH increases. (more alkaline)

try to figure out the others using the same logic.