Quiz Time

1. Quiz Time 05:00 04:00 03:00 02:00 01:30 01:00 00:45 00:30 00:15 00:00

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3. Last Week • Synthesized chloropentaaminocobalt chloride [Co(NH3)5Cl]Cl2 • Determine theoretical yield (mass) of product

4. Goals for This Week • Determine % yield of product • Analyze product by cation exchange column chromatography to determine charge • Analyze product by Atomic Absorption Spectroscopy (AAS) to determine its % mass composition of cobalt

5. Hazards • Product • NaOH

6. The Analyses • Three types • %Yield • Charge analysis – _______________________ • Amount of cobalt present - ____________ • What will they tell us? • %Yield  • Charge  • Mass% Co 

7. % Yield • What does it tell? • %Yield= • Theoretical yield • Weigh amount of ____________________ • Change grams to moles • Determine how many moles of product this could make • Take into account ______________ • For this expt: ___________________ • Change to __________ of product

8. Ion Exchange Chromatography (IEC) • Absorption column chromatography OR Affinity Chromatography • Chromatography – _____ ______ – separation of mixture based on specific property of mixture • In our case, the property that we want to study is the ________, therefore the separation is based on the ________ • Cobalt is a cation • Therefore, we use _____ exchange chromatography • Cation exchange chrom. uses exchangeable cations • Anion exchange chrom. uses exchangeable anions

9. IEC continued • Columns packed with synthetic polymeric resin • Cations are able to displace the H+ ions • What happens to pH of effluent (the stuff coming off of the column) when H+ goes into solution?

10. IEC continued Number of H+s “kicked off” is dependent on number of positive charges replacing them • If cation has +1 charge, will kick off 1 H+s • If cation has +2 charge, will kick off 2 H+s [Co(NH3)5Cl)]2+

11. IEC continued • Therefore, if you can tell how many H+s are kicked off and you know how much of the substance you added to the column, you can tell how many complex charges stick • How do you determine how many H+s? • What is the indicator?

12. IEC Column Prep • Choose a column that has at least ½” of yellow bed • NEVER allow column bed to get dry • Never trust anyone who used equipment before you • Columns will still have Co and may still have HCl on column • How does this affect us? • How do you get rid of HCl? • Wash column with deionized (d.i.) water • You must remove cork in order for column to drain • Check effluent with pH paper until same pH as d.i. water

13. IEC Analysis • Weigh sample (only using 0.2g (very small %)) of sample • Dilute sample • Apply aliquot of sample to column • Flush column with d.i. water • Collect effluent in flask (to be titrated) • Continue collecting until pH paper turns same color as d.i. Water to be sure that all sample binds and all H+s are collected • Titrate the effluent with standardized NaOH

14. IEC Results • Theoretically • Final product had +2 charge • Can you get something else? • What does the charge that you get depend on? • HCl:NaOH = 1:1 molar ratio • In expected complex, Comp:HCl = 1:2 • Therefore, expect NaOH:Comp = 2:1 • Ionic charge = MNaOH*Vtitrated (masssample/mwcomplex)*dilution = mol NaOH/mol complex • If ratio is not 2.00, you should explain why

15. Atomic Absorption Spectrometry • Finding mass% of Cobalt atoms in sample • UV-vis spectrometer was used in sports drink lab • Similar guiding principles • Be sure to use d.i. water so no ion interference

16. How Does AAS Work? • Instrument heats sample to change into vapor state • Flame causes decomposition into elements • Elements = atom = Co for us • Light travels through sample that is in gaseous phase, each element has specific  that it will absorb • Electromagnetic radiation is absorbed by atoms of interest • Absorbance is determined in similar fashion as in UV-vis spec

17. How Does AAS Determine Concentration? • Using standards, you can make _____________ ___________ just like in sports drink experiment • Then, sample is run and computer uses ______ __________________ to indicate concentration • Given in ppm (parts per million) = 1/106 = 10-6 = mg/L

18. Advantages of AAS • Quick • Standards ~ 5 minutes • Samples ~ 1 minute each • Very sensitive • Can detect trace amounts of atoms in sample • Very small amount of sample needed • None of the other atoms in complex interferes • Therefore, impurities, etc. do not get detected

19. AAS Results • Theoretical %Co [Co] = (atomic mass Co/mw complex)* 100% • Actual %Co • Your value will be given in mg/L or ppm • 0.2xxxg of sample in 100mL dilution • Diluted again, 5mL to 500mL • Compare actual value to theoretical value of the expected product (and different intermediates) and tell what it means about what you have for your “product”

20. Results Summary • What does %yield tell you? • What could cause this value to be other than 100%? • What should the final charge be for the product? • Can you get something else? • What does the charge that you get depend on? • How much cobalt should be in the product? • You know how to calculate expected mass% when given chemical formula • What if you determine that it is not the calculated value?

21. Applications of Methods • Column Chromatography • Useful step in many types of purifications or analyses • You must know some physical characteristics of the substance (ie charge) • Example: Protein purifications • AAS • Used to detect trace quantities of metals • Can be used when not enough present to perform titrations, etc. because of sensitivity • Example: can be used to monitor drinking water to ensure that levels of lead, arsenic, etc. are within limits