Application of Aqueous Equilibria

# Application of Aqueous Equilibria - Application of Aqueous...

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Application of Aqueous Equilibria Chapter 15 Common ion: an ion that comes from more than one source in the formation of a solution. Common ion effect: the equilibrium position shift caused by the presence of a common ion. Equilibrium calculations are similar to what we did before only know the initial concentration of A - is not zero. Buffered solution: a solution the resists changes to its pH when wither strong acids or bases are added; consists of a weak acid and its salt or a weak base and its salt. Steps to solving a buffered solution problem: 1. Find the original pH of the buffered solution. 2. Do the stoichiometric calculations to determine the new concentrations (assume H + and OH - react to completion. 3. Do the equilibrium calculation. 4. Calculate the new pH and compare it to the original pH of the buffered solution. Henderson – Hasselbach equation: another way to solve for the pH of a buffered solution: pH = pK a + log([A - ]/[HA]) Buffering capacity: the amount of protons or hydroxide ions that can be absorbed without significant changes in the pH. The pH of a buffered solution is determine by the ration [A - ]/[HA]. The capacity of a bufferes solution is determined by the magnitudes of [A - ] and [HA]. Can use the equation [H + ] = K a [HA]/[A - ] to determine the best ratio to get a buffer of a particular pH. Titration (pH) curve: shows how the pH of a solution changes as more titrant is added. Often use millimoles (mmol) as the unit because then we can avoid having very small numbers of moles. Equivalence (stoicihometric) point: the point on the titration curve where the number of moles of acid is equal to the number of moles of base. For a strong acid + strong base titration this always has pH = 7.0. Solving a weak acid with a strong base is a two step problem: 1. A stoichiometry problem for the acid-base reaction going to completion.

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2. An equilibrium problem for the ions remaining in solution. Remember that the volume is increasing, therefore the concentration will be decreasing. Half equivalence point for a weak acid with strong base:
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## This note was uploaded on 07/22/2008 for the course CHEM 105A taught by Professor Bau during the Summer '04 term at USC.

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Application of Aqueous Equilibria - Application of Aqueous...

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