AcidAcid / Base Titration – K a (HAc)BaseTitration AcidAcid / Base Titration – K a (HAc)BaseTitration Hand in: Pre-Lab and Equilibrium report and Submit Group Form OPEN EXCEL Today - Weak Acid: HA(aq) H + (aq) + A - (aq) Determine K a by performing a titration: CH 3 COOH(aq) + NaOH (aq) NaCH 3 COO(aq) + H2O (l) about 0.1M M in 2011 We can use the 1:1 molar relationship and titration endpoint to determine exact M of Acetic Acid (like prelab question #2) – how do we know the endpoint? WE MAKE A TITRATION AND DERIVATIVE CURVE

AcidAcid / Base Titration – K a (HAc)BaseTitration AcidAcid / Base Titration – K a (HAc)BaseTitration Set up EXCEL with active titration graph Column A – mLs of NaOH added – sig figs dictated by buret Column B – pH (standard units) of solution Column C – Derivative (ΔpH/Δ Volume) or (B3-B2/A3-A2) Set up for real time graph (pH vs. volume added) Set up Titration Apparatus Stirring Plate, Ring Stand, Clamp (for pH probe), Burette Holder, Burette Rinse Burette with 0.1 M NaOH, no bubbles, Fill with NaOH to 0.00 mL Add mL of Acetic Acid to clean, dry beaker (use volumetric pipet) Add 50.0 mL of DI water using grad cylinder Add 4-5 drops of Phenolphthalein Add stir bar

AcidAcid / Base Titration – K a (HAc)BaseTitration AcidAcid / Base Titration – K a (HAc)BaseTitration Perform Titration Calibrate the pH probe use manual instructions use pH 7.00, then pH 4.00 Always rinse probe with DI water, then dab dry gently BE PATIENT WHEN WAITING FOR FLASHING NUMBER TO STOP!!! Begin Titration Add 1 mL increments until pink color fades slowly Switch to 0.10 to 0.20 mL increments Record EXACT volumes and stabilized pH values As you get closer to endpoint, derivative value will jump continue past endpoint until your values stabilize (above pH 10) “Save” (and save often) your file(s) – perform titration 3x’s

K a Calculation: HA H + + A - Conc’ns[HA][A - ] Initial1 M0 M ¼-equiv¾ M¼ M ½-equiv½ M ¾-equiv¼ M¾ M Decimals in pH = Sig Figs in [H + ]

AcidAcid / Base Titration – K a (HAc)BaseTitration AcidAcid / Base Titration – K a (HAc)BaseTitration

Lab Report Title Page Purpose Results - Three Titration/Derivative Graphs (don’t need data columns) one with ¼, ½, and ¾, and endpoint clearly marked endpoint clearly marked on other two - Data Sheet (with sample calculations) - Present/Staple in order data/calculations were obtained/performed - Significant Figures and Units Conclusion [ Errors, Improvements ] Individual Checked-Pre-labs Lab Report Due Next Week