11.20 - Chem 102B Discussion Worksheet#22 Titration Curves...

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Chem 102B – Discussion Worksheet #22 Titration Curves 1. Initial pH Strong Acids and Bases The pH is determined based solely on the initial concentration of the acid or base being titrated. Every mole of acid or base will produce once mole of H + or OH - . Exception: Bases formed with Group II cations will form two moles of OH - for every mole of base, e.g. Ca(OH) 2 . pH = -log[H + ]; pOH = -log[OH - ]; 14.00 = pOH + pH. Weak Acids and Bases The pH of these solutions are determined by the initial concentrations of the acid or base and the dissociation constants K a or K b . K a = [H + ][A - ]/[HA] K b = [OH - ][BH + ]/[B] Where, HA is the initial concentration of the weak acid, and [B] is the initial concentration of the weak base. In the case of polyprotic acids, only the most acidic K a is used to calculate the initial pH. 2. pH during the titration For every mole of OH - added to an acid (strong or weak) one mole of acid will be neutralized. For every mole of H + added to a base (strong or weak) one mole of base will be neutralized. Strong Acids and Bases Neutralization of one mole of a strong acid (H + ) or strong base (OH - ) will produce one mole of water. H + + OH - Æ H 2 O The pH is determined by calculating the number of moles of unreacted acid or base remaining in solution. Original moles of acid – moles OH - = remaining moles of acid
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The number of moles of remaining acid are then divided by the total volume of the solution (original volume of acid + volume of added base) to get the [H + ]; pH = -log[H + ] Weak Acids and Bases
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11.20 - Chem 102B Discussion Worksheet#22 Titration Curves...

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