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Your Lab Final - 21 points

Your Lab Final - 21 points. 25-30 min on the last day of lecture, Wed Dec 9 Short answer & multiple choice Bring your calculator & common sense Review your old labs Take note of basic calculations (including stats), chemical equations, techniques used.

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Your Lab Final - 21 points

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  1. Your Lab Final - 21 points • 25-30 min on the last day of lecture, Wed Dec 9 • Short answer & multiple choice • Bring your calculator & common sense • Review your old labs • Take note of basic calculations (including stats), chemical equations, techniques used

  2. Volumetric Determination of Zinc and Calcium Using Complexometric Titration First Week: 1) Preparation and Standardization of EDTA solution (10ppt) – save for week 2 2) Use SciFinder Scholar or Web of Science to find reference (page 3) Second Week: 1) Analyze Water Sample for Ca2+ You must do this first!!! Geology will use your data! 2) Analyze Cold-Eeze Lozenge for Zn2+ 3) Check-in & Course Evaluations

  3. 4 Classes of ReactionsUsed quantitatively Precipitation Gravimetric Ca: calcium oxalate Acid/Base Volumetric Acid: KHP + OH¯ Redox Gasiometric Nitrite: NO2- + H+ NH2SO3¯→ N2 + HSO4¯ + H2O Complexation This lab – our final experiment! Volumetric Ca & Zn: EDTA

  4. Development of Cold-Eeze Lozenges One of the people involved in the designed to reduce the duration and severity of the common cold by introducing zinc ions into the body is J. C. Godfrey We are going to get one of the references in his research that talks about this research to treat the common cold, using Scifinder Scholar or Web of Science. The Libraries of The Claremont Colleges You will do this in the computer room (113) after completing standardization. Write down the reference and a one sentence summary of the abstract in your report.

  5. Polydentate or Multidentate Ligands Like :NH3 1 Ligand, but 2 bonds Like CO32- Called Chelates (claw)

  6. 2 1 5 6 3 4 Fully deprotonated EDTA can bind to metal ion at 6 sites

  7. Eriochrome Black- T Indicator Deprotonated indicator (In-)in the presence of excess metal ions (Mg+2) forms a wine-red complex (MgIn-) Add EDTA → at the endpoint MgEDTA forms InH turns greyish – blue Make mock solution for comparison Note that there are 2 different indicators- one for Ca+2 and one for Zn+2

  8. Week 1 – Standardize EDTA Preparation of the CaCO3 in beaker, transfer to volumetric flask Prepare 500 ml of a 0.020 M EDTA solution Use 250 ml volumetric flask to the markemptying (2x) into a clean 800 mL beaker, repeat. Dissolves slowly (> 5 min). Heat if necessary but cool before titrating. Also, after titrating (3 trials, 5-10ppts), use SciFinder Scholar or Web of Science in 113. If time permits, titrate water sample (step 3, page 4).

  9. Week 2 – Evaluations, Water and Lozenge Analysis, Check out Titrate water samples Water hardness results go to Prof.Reinen of Geology (obtain 100mL from lab assistant) Use 6-7 drops of indicator Titrate three lozenges Make buffer solution Remember to take masses of each before crushing with mortar & pestal and determine amount used in each titration

  10. How are you going to make the buffer? • pH = pKa + log [A-]/[HA] where A- = acetate ion in this case • [HA] = 0.02500L (1.00M)/0.250L = 0.100 M • pKa (HA) = 4.74 • 5.5 = 4.74 + log [A-]/0.100 • [A-] = 0.5754 M • n(A-) = 0.5754 M (0.2500L) = 0.1439 moles • m(NaA3H2O) = 0.1439 moles (136.08 g/mole) = 19.6 grams for the hydrate • m(NaA) = 0.1439 moles (82 g/mole) = 11.8 grams for the anhydrous salt

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