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Kh pacidbaseneutralization[1]slide onechm 240xxxxxxxxxxxxxxxxxxdont let go (2)

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  • 1. PURPOSE: • To standardize a solution of sodium hydroxide by titration with a primary standard, potassium hydrogen phthalate (KHC8H4O4)
  • 2. Use ph electrode
  • 3. ANALYTICAL CHEMISTRY • Determination of iron in a razor blade • Determination of acetic acid in vinegar • Determination of Alcohol in Blood
  • 4. Must do three things before You start • • • • • • • 1. Clean the Buret 2. Delivering Solution from the Buret 3. Filing the Buret for a titration 4. Preparing the KHP Sample 5. Titrating the KHP * Must use Your Lab book today! *** This is one of the MOST complicated labs
  • 5. KHP
  • 6. Why use KHP? • The hydrogen is slightly acidic, and it is often used as a primary standard for acid-base titrations because it is solid and air-stable, making it easy to weigh accurately. It is not hygroscopic. It is also used as a primary standard for calibrating pH meters
  • 7. as a buffering agent • As a weak acid hydrogen phthalate reacts reversibly with water to give hydronium (H3O+) and phthalate ions. HP- + H2O <->P2- + H3O+ • KHP can be used as a buffering agent(in combination with hydrochloric acid (HCl) or sodium hydroxide (NaOH) depending on which side of pH 4.0 the buffer is to be)
  • 8. What I would like . . . • In this experiment you will determine the amount of acid needed by titration with the strong base NaOH.
  • 9. What is a standardization??? • Since it is hard to prepare a NaOH solution of accurately known concentration directly from the solid, you will need to standardize your NaOH solution against a precisely weighed amount of standard acid. • The acid used is the weak monoprotic acid, potassium hydrogen.
  • 10. Excellent to use!!! Can actually obtain 1 mole of H+ by using a balance
  • 11. A titration • Knowing the volume of titrant added allows the determination of the concentration of the unknown. Often, an indicator is used to usually signal the end of the reaction, the endpoint
  • 12. acid-base indicator • An acid-base indicator is itself a weak acid (or its conjugate base). • An acid-base indicator is a weak acid having a different colour in aqueous solution from its conjugate base.
  • 13. phenolphthalein
  • 14. phenolphthalein • Phenolphthalein • Type: HIn + H2O <->In- + H3O+ pK: 9.5 Approximate pH range for color change: • 8.0-9.8 Color of acid form: clear Color of base form: red-violet
  • 15. phenolphthalein
  • 16. Commonly used equipment • • • • Buret Erlenmeyer Flask Magnetic Stir Plate Electronic Balance
  • 17. accuracy • The accuracy of the results of your titration will be a reflection of the care you took while performing it. When done carefully, titrations give very accurate, precise results. •
  • 18. accuracy • SOMETIMES!!!!!!! • Titrations of unknown solutions are done in two steps: a scout titration used to determine the approximate amount of titrant needed followed by the actual titration that you will use to make your calculations.
  • 19. What You will do . . . • An 0.8167 gram sample of primary standard KHP (assay = 99.95%) required 38.25 mL of NaOH to neutralize. Calculate the molarity of the NaOH solution.
  • 20. Goto pdf. . . . • Path: XXXX g sample -> g KHP -> mol KHP -> mol NaOH -> M NaOH
  • 21. path 0.8167 g sample x (99.95g KHP)/(100 gram) x (1molKHP)/(204.22g KHP) x (1mol NaOH)/(1 mol KHP) x (1 )/(0.03825 L)= 0.1040 M NaOH
  • 22. Using the pH Probe
  • 23. Using the pH Probe • Using the pH Probe • Preparation of the pH Sensor • A pH sensor connected to a computer will be used to measure pH. Plug the pH probe into channel 1 of the interface box. Plug the power cord on the interface box into an electrical outlet.
  • 24. Using the pH Probe
  • 25. Best site • http://www.chemistry.mtu.edu/~djchesne/cla sses/ch2212/Tutorials/Vernier_pH_tutorial.ht m
  • 26. Arrhenius acids.
  • 27. The net ionic equation H + (aq) + H2O(l) <-> H3O + (aq) • Pure water already contains small quantities of the H + ion (proton), H3O + (hydronium ion)
  • 28. On Exam • Example: Calculate the weight of primary standard potassium hydrogen phthalate • (assay = 99.95%) that would be required to standardize a 0.1 N NaOH solution, • assuming a 40 mL titration. • PATH: L NaOH  mol NaOH  mol KHP  KHP  g g sample • Note that 1 equiv = 1 mol for both KHP and NaOH so N = M and molecular weight = equivalent weight.
  • 29. • Example: An 0.8167 gram sample of primary standard KHP (assay = 99.95%) required • 38.25 mL of NaOH to neutralize. Calculate the molarity of the NaOH solution. • PATH: g sample  KHP  g mol KHP  mol NaOH  NaOH M
  • 30. • Example: A 1.7734 gram sample of KHP required 40.11 mL of 0.1036 N for titration. • Calculate the assay of the KHP and report with a relative error of 1 part per 1000.