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Volumetric Analysis: Titration

Volumetric Analysis: Titration. An introduction. The Big Picture. Use a solution of known concentration (the standard solution) to determine the concentration of an unknown solution. What we need. The chemical equation A way to measure amounts of solution added

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Volumetric Analysis: Titration

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  1. Volumetric Analysis: Titration An introduction

  2. The Big Picture Use a solution of known concentration (the standard solution) to determine the concentration of an unknown solution

  3. What we need • The chemical equation • A way to measure amounts of solution added • Fixed and variable • A way to determine that the titration is complete • Reaction should be fast

  4. The Chemical Reaction • Must know the equation and correct stoichiometric ratios Example: Write the equation for the titration of sulfuric acid with sodium hydroxide NaOH(aq) + H2SO4(aq) Na2SO4(aq) + H2O(l) 2 2 Not balanced Therefore the base to acid ratio is 2:1

  5. Volume Measurements • Titrate a variable amount of solution into a known volume of solution until titration is complete Fixed (known) volume should be measured with high precision: Use pipette (p.17) Variable volume should be as high precision as possible: Use burette

  6. How to determine titration is complete • Usually an indicator is used • Terms • End point: when indicator changes color • Equivalence point: when a stoichio-metrically equivalent amount of titrant has been added to solution

  7. More on indicators Phenolphthalein is a very common acid-base indicator Colorless in acid Pink in base

  8. Example 25.00 mL of 0.460 M sulfuric acid is titrated with NaOH, requiring 28.45 mL to reach the endpoint. What is the NaOH concentration?

  9. Example We place 25.00 mL of acid and a couple drops of the indicator into the flask and titrate with base until the solution turns slightly pink. 2 NaOH(aq) + H2SO4(aq) Na2SO4(aq) + 2 H2O(l)

  10. Example 25.00 mL of 0.460 M sulfuric acid is titrated with NaOH, requiring 28.45 mL to reach the endpoint. What is the NaOH concentration?

  11. Example Moles of acid Moles of base Concentration of base

  12. Some Titration Techniques • Start with burette at or beyond 0.00 mL • It doesn’t matter, just record it! • Don’t waste time getting exactly 0.00 mL • Titrate to the ½ drop • Add extra water if needed • How does this affect calculations?

  13. Some Titration Techniques • Stir! • Place on white paper • Palest and most reproducible pink possible

  14. Common Abbreviations for Acetic Acid CH3COOH HCH3CO2 C2H4O2 C2H3O2H HOAc

  15. This Week’s Analysis Goal: Determine molar concentration and mass percentage acetic acid in vinegar Units of concentration of acetic acid in vinegar: Units on mass % of acetic acid in vinegar:

  16. This Week’s Analysis • Oxalic acid as a primary standard • Why? • One oxalic acid solution per 2 groups • Note that oxalic acid is a hydrate • How does this affect you? • 10 mL pipettes • 250 mL volumetric flasks

  17. Procedure Proposal How you will prepare your oxalic acid solution (~0.25 M) How you will determine NaOH concentration including calculations and chemical reactions How you will determine the concentration of the acetic acid in vinegar (and how many trials) Road map of calculations for calculating C and mass % acetic acid from your data Don’t even think of using C1V1=C2V2

  18. This investigation, Author 3: Introduction and Conclusion 1: Discussion 2: Data/Results and Experimental This investigation, Author A: Introduction, Conclusion, Data/Results B: Discussion and Experimental

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