FINAL_REVIEW_part_2 - 1. Titration of weak acid with a...

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Unformatted text preview: 1. Titration of weak acid with a strong base: a. Titrate 15mL of 1.2M HF (Ka = 7.2 10-4) with a 2.0M NaOH solution. Find pH: When no base added 4.5mL of base added 6.25mL of base added 9mL of base added 13mL of base added General equation of weak acid w/ strong base: HA + OH- H2O + A- Equation for this problem: HF + NaOH NaF + H2O No Base Added--Point A: - What is in Solution?--only weak acid (HA), in this case HF - Since [HA]i [H3O+], need to do a Ka ICE table equilibrium calculation to find [H3O+]. - - 4.5mL of Base Added--Region A': - Has some OH- OH- reacts immediately to form some H2O and A- HA + H2O H3O+ + AStress: [HA], [A-] Equilibrium shifts left, suppresses formation of [H3O+] pH takes an initial "jump" 6.25mL Base Added--Region B: - More OH- added causes more A- formation - Initial mol HA > mol OH- added - What is in solution here?--some A- and some unreacted HA - This is a BUFFER! b/c weak acid + conj. base--use H-H eqn. to get pH - Do a limiting reactant problem to get mol A- and mol HA 9mL Base Added--Point C: - Initial mol HA = mol OH- added - Any HA left?--No - Any OH- left?--No - What is in solution here?--NaA--really A-, since it is conj. base of a weak acid, you know you have a pH>7 (use this as a check to make sure you're doing the problem correct) - Need to do a Kb ICE table calculation - Before this though, need: Value of Kb Initial [A-] for your "I" line in ICE table [A-] = mol A- formed = mol HA initial total volume (L) total volume (L) - Kb [OH ] pOH pH 13mL Base Added--Region D: Here, moles base added > initial moles acid. - Do a limiting reactant problem to find excess moles of OH- Divide these moles by the total volume in liters - [OH-] pOHpH REMEMBER!!--Treat every titration problem as a brand new problem! ...
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This note was uploaded on 05/17/2008 for the course LBS 172 taught by Professor Laduca during the Spring '08 term at Michigan State University.

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FINAL_REVIEW_part_2 - 1. Titration of weak acid with a...

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