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Acid / Base Titration – K a (HAc)

Acid / Base Titration – K a (HAc) . 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:

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Acid / Base Titration – K a (HAc)

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  1. Acid / BaseTitration – Ka (HAc) • Hand in: Pre-Lab and Equilibrium report and Submit Group Form • OPEN EXCEL • Today - Weak Acid: HA(aq) H+(aq) + A-(aq) Determine Ka by performing a titration: CH3COOH(aq) + NaOH (aq) NaCH3COO(aq) + H2O (l) about 0.1M 0.0986 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

  2. Acid / BaseTitration – Ka (HAc) • 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 25.00 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

  3. Acid / BaseTitration – Ka (HAc) • 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

  4. Ka Calculation: HA H+ + A- Decimals in pH = Sig Figs in [H+]

  5. Acid / BaseTitration – Ka (HAc)

  6. 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

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