Quiz Time

05:0004:0003:0002:0001:3001:0000:4500:3000:1500:00

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Last Week Synthesized chloropentaaminocobalt

chloride [Co(NH3)5Cl]Cl2 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 continuedNumber 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

+

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 = MNaOH*Vtitrated

(masssample/mwcomplex)*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) = 1/106 =

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

%100mL1000

L1

mg1000

g1

mL5

mL500

)g(samplemass

mL100Co/L ??mg %Co

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