Quiz Time 05:00 04:0003:0002:0001:3001:0000:4500:3000:1500:00

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Last Week Synthesized chloropentaaminocobalt chloride [Co(NH 3 ) 5 Cl]Cl 2 Determine theoretical yield (mass) of product

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

Hazards Product NaOH

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

% 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

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

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?

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(NH 3 ) 5 Cl)] 2+

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?

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

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

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 = M NaOH *V titrated (mass sample /mw complex )*dilution = mol NaOH/mol complex If ratio is not 2.00, you should explain why

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

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

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) = 1/10 6 = = mg/L

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

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”

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?

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