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Chapter 15 and 16: Acid Base Equilibria and solubility Constants

Chapter 15 and 16: Acid Base Equilibria and solubility Constants. 15.1 Solutions with common ions. What is a common ion? Ion produced by an aqueous acid or base as well as a salt that is dissolved Ex: Hydrofluoric Acid (HF) and Sodium Fluoride ( NaF ) share fluorine ion as the common ion

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Chapter 15 and 16: Acid Base Equilibria and solubility Constants

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  1. Chapter 15 and 16: Acid Base Equilibria and solubility Constants

  2. 15.1 Solutions with common ions What is a common ion? • Ion produced by an aqueous acid or base as well as a salt that is dissolved • Ex: Hydrofluoric Acid (HF) and Sodium Fluoride (NaF) share fluorine ion as the common ion • Fluoride ion attracts hydrogen ions to it from water when dissolved in solution • Equilibrium will shift away from common ion since it takes hydrogen ions with it

  3. 15.1 • Because the fluoride ion is taking away hydrogen ions, the pH of the solution will be greater than expected (Less acidic) • So in this case the common ion (Fluoride) has changed the ph of the solution via its electrostatic attractive properties • Similar effects are observed when the ammonium ion (NH4+) is placed in water. • The ammonium ion attracts oh ions and so the pH decreases and is more acidic than predicted

  4. 15.1Common Ion Effect • The general rule is that common ions can make acids less acidic by attracting the hydrogen ions that would otherwise have been free in solution, thus increasing the pH • And, a common ion can make a solution less basic by attracting the hydroxide ions that would have been free in solution, thus decreasing the ph. • In either situation, a key ion concentration has been reduced because of the common ion • In all cases a shift in equilibrium has occurred as a result of the actions of the common ion

  5. 15.2 Buffered Solutions • These solutions are examples of applications where common ions are used to maintain a ph • Buffered solutions by design resist changes in ph when an acid or base has been added to the solution • Contain 1 of 2 possible combinations • Weak acid and its common ion salt • Weak base and its common ion salt

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