Common Ion Effect: pH of LiF, KI & NH4Cl Solutions

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SUMMARY

The discussion focuses on the common ion effect and its impact on the pH of solutions when specific salts are added. When LiF is added to an HF solution, the pH increases due to the increase in F- concentration, which disturbs the equilibrium and favors the backward reaction, decreasing H+ concentration. In contrast, adding KI to an HI solution does not change the pH, as the I- ion does not significantly affect the equilibrium. Lastly, the addition of NH4Cl to an NH3 solution results in a decrease in pH due to the formation of NH4+, which increases H+ concentration.

PREREQUISITES
  • Understanding of chemical equilibrium principles
  • Knowledge of the common ion effect
  • Familiarity with weak acids and their conjugate bases
  • Basic grasp of pH calculations and definitions
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  • Study the common ion effect in detail using examples from various weak acids and their salts
  • Learn about Le Chatelier's Principle and its applications in chemical equilibria
  • Explore the pH calculations for buffer solutions and their components
  • Investigate the behavior of other salts in acidic and basic solutions
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Chemistry students, educators, and anyone seeking to understand the effects of ionic compounds on pH and chemical equilibria.

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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



 
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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.
 

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