CHE 104 Chapter 17 Outline - CHE 104 Chapter 17 Applications of Equilibrium Common Ion Effect o The shift in equilibrium that occurs because of the

CHE 104 Chapter 17 Outline - CHE 104 Chapter 17...

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CHE 104 Chapter 17 Applications of Equilibrium Common Ion Effect o The shift in equilibrium that occurs because of the addition of an ion already involved in the equilibrium reaction AgCl( s ) Ag + ( aq ) + Cl ( aq ) Adding NaCl ( aq ) shifts equilibrium position A Buffered Solution o Resists change in its pH when either H + or OH - are added o 1.0 L of 0.50 M H 3 CCOOH + 0.50 M H 3 CCOONa pH = 4.74 Adding 0.010 mol solid NaOH raises the pH of the solution to 4.76, a very minor change Key Points on Buffered Solutions o They are weak acids or bases containing a common ion . o After addition of strong acid or base, deal with stoichiometry first, then equilibrium. Example 1 (pH of a buffered solution) Example 2 (pH changes in buffered solutions) Example 3 (pH of a buffered solution) Henderson-Hasselbalch Equation o Halfway point = pH = pKa o Useful for calculating pH when the [A - ]/[HA] ratios are known o pH = p K a + log([A - ]/[HA]) = p K a + log ([base]/[acid]) Example 4 (Henderson-Hasselbalch equation) Buffered Solution Characteristics o Buffers contain relatively large amounts of weak acid and conjugate base. o Added H + reacts to completion with the weak base. o Added OH - reacts to completion with the weak acid. o The pH is determined by the ratio of the concentrations of the weak acid and weak base. Buffering Capacity o Represents the amount of H + or OH - the buffer can absorb without a significant change in pH.

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