Chem 14BL- Week 7 Notes
Chem 14BL- Week 7 Notes CHEM 14BL
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This 7 page Class Notes was uploaded by Daniel Ochs on Friday May 13, 2016. The Class Notes belongs to CHEM 14BL at University of California - Los Angeles taught by Casey in Spring 2016. Since its upload, it has received 12 views. For similar materials see General and Organic Chemistry Laboratory I in Chemistry and Biochemistry at University of California - Los Angeles.
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Date Created: 05/13/16
Week 7 Notes Weak Acit Titration with Strong Base 1. Initial pH before any titrant added: Regular dissociation 2. pH prior to the equivalence point: Calculate the fraction of the titrant that has been titrated 3. pH at equivalence point: Calculate the pH of a solution due to neutralization. Include dilution that has occurred during the titration 4. pH after the equivalence point Calculate the dilution of the excess titrant Point (1): intial pH of weak acid 5% Rule: Assumption used to simplify calculation. If x is less than 5% of initial concentration than dissociation can be considered negligible (0.1 M − x ≈ 0.1 M) Point (2): pH prior to equivalence point Some amount of strong base (titrant) has been added. For this example, let us assume 30.00 mL of NaOH is added. First, determine amounts (moles) of acid and base reacting in the neutralization reaction. Next, determine the amounts of HA left after neutralization and amount of A formed by stoichiometry Finally, determine pH after equilibrium (concentrations) has reestablished Point (3): pH at equivalence point An amount of strong base (titrant) equal to the initial amount of acid present has been added. By deﬁnition, we know that the amounts (moles) of acid and base reacting in the neutralization reaction are equal. Therefore, all HA will be neutralized and leave an amount of A equal to the OH added - The pH is determined by the equilibrium of A - Point (4): pH after the equivalence point An amount of strong base (titrant) exceeding the initial amount of acid present has been added. Any additional titrant added beyond the equivalence point can no longer be neutralized and will contribute to the excess titrant in solution. The excess base added represents the main source of [OH] in solution, the [OH] resulting from the reaction of A with water is negligible Condiering Equilibrium Let’s take a quick quiz! 1. ou have a weak acid in a ﬂask and it dissociates. Is the reaction at equilibriumes-Y 2. ou add strong base to the weak acid. After the two reagents have reacted, is the reaction at equilibrium? -es 3. ou add enough strong base to reach the equivalence point. Is the reaction at equilibriues -Y
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