Chem 360 Final Exam

Chem 360 1

April 2004 Chem 360 Final Exam T. Smith-Palmer

Part I

[9] 1.Choose three of the following detectors and describe what they do and how they do it. Include a diagram for each to assist your explanation.

(a) Solid state scintillation counter

(b) FID

(d) ECD

(e) Proportional counter

[2] 2.How is Cobalt-60 prepared from cobalt-59?

[2] 3.Please rewrite the following using correct spelling and grammar:

Ions were seperated by Capilary Electrophesis before being detacted by flourescence. After the substance was grinded, a large ammount of percipitate was seen. A filtration was then preformed.

[6] 4.One of the problems with CE is that the LOD, in terms of concentration, can be much higher than the LOD for HPLC.

(a)Why is this so?

(b)Why did I say ‘in terms of concentration’?

(c)You could lower the LOD by using S.P.E., stacking, or using a capillary with a bulge where the light passes through. Explain two of these options in detail.

[12] 5. The crime scene was buzzing with activity.

One victim was lying face down in a bathtub of water. There was evidence of a white powder, possibly a drug, in a glass by the bath. The victim had been shot and several possible suspects were being held in custody. A bullet had been found, but was greatly deformed by its impact with the cast-iron bath. There appeared to have been a struggle as there was blood near the bath, but no evidence to suggest that it had come from the victim. Paint had been removed from the wall and some had been found on a suspect’s jacket.

Suggest six analyses that could be done to help solve the crime.

For each state the species that is determined and the instrumentation/method used.

[5] 6. Choose one mass analyzer. Describe its purpose and its principle of operation.

Include a diagram.

Give one limitation of this kind of mass analyzer.

[10] 7.You are working in a large research lab and have been told that there is money available to purchase an instrument for your lab. You must fill out the following form to submit to your senior officer. It should justify your recommendation.

Be creative as to what you want to analyze – but then make sure all your answers fit with one another.

Recommendation for Instrument purchase

Are you in the Organic or Inorganic analytical division?

Species to be analyzed:

Instrument recommended:

What can this instrument ‘do’?

i.e. why are you particularly recommending this instrument?

What is a typical LOD for these kinds of analysis?

How versatile is it?

i.e. what other kinds of things could it be used to analyze once this project is finished. Mention if this would require any changes to it.

What drawbacks/disadvantages are there?

[15] 8.Discuss “The Importance of Stationary Phase in Chromatography”.

Hints: You may write in note or point form. For an idea how much to write – this question should be allotted 27 minutes of your time. For 15 marks, you should have made at least 15 ‘points’ in your answer. Brief/minor points will be worth half marks.

What does it do?

How does it do it?

Why are there many different kinds? How would you choose one?

What would an ideal stationary phase be like?

What parameters dictate how well it performs.

Include the van Deemter equation. Discuss the parameters involved which are associated with the stationary phase.

Part II – Lab Questions

1. Do 3 of the following:

[3] (i)What was the purpose of the suppressor in ion chromatography?

Differentiate between the suppressor we used with the current ‘ON’, and how we might use a simpler suppressor with no current or voltage involved.

[3] (ii)Predict the order of elution of the following ions on an anion exchange chromatography column:

Bromide, chloride, fluoride, sulfate.

Suggest a suitable eluent.

[3] (iii)Choose either gas or liquid chromatography. Then give three ways to increase resolution on the chosen instrument without changing the column.

[3] (iv)Starting with a phosphate buffer, what other components need to be added to separate the following types of analytes by capillary electrophoresis:

(a) anions

(b) neutrals

[3] (v)Which of the following species can be determined using polarography:

Azobenzene

Sodium ions

Zinc ions

Ferric ions

Aluminum ions

Magnesium ions

Cadmium ions

Vitamin C

Suggest a species that could be determined:

[7] 2. DO EITHER

Choose one form of voltammetry:

Decide on a particular species to analyze:

Answer the following questions about it:

(a)What is the working electrode?

(b)What species are you analyzing?

(c)Is it an oxidation or reduction at the working electrode?

(d)What needs to be added to the sample before analysis?

(e)Sketch the form of the Voltage versus time curve.

(f)Sketch the form of the current versus time curve that will result when your chosen species is analyzed.

(g)How could you decrease the limit of detection?

(a) What are some advantages of using a mercury drop as an electrode?

(b) What are some disadvantages?

(c) Assuming you have a solenoid in the mercury column to control the mercury (as we have in our instrument), sketch a graph of drop size versus time.

(d) What is the advantage of current sampling?

(e) Describe one pulse sequence that is used in voltammetry.

(f)What is the advantage of using a pulse sequence?

Part III – Problems

[5] 1. DOEITHER

A substance C, which is not retained in the stationary phase, exits from a chromatography column 5.0 min after injection. Another substance D, which is retained, exits in 20.0 min. The flow rate of mobile phase is 25 mL/min.

(a)How long does D spend in the mobile phase?

(b)How long does D spend in the stationary phase?

(c)What is the value of k′ for D?
(d)What is the retention volume, VR, for D?
(e)What is Vm?
OR
The following data are obtained from a GC analysis: tR = 10.0 min, W = 0.30 min, tair=0.50min, Vs = 4.0 mL, and F = 40 mL/min. Calculate:
(a)k′ (capacity factor)
(b)Vm (mobile phase volume)

(c)KD (distribution coefficient)

(d)VR (retention volume)

(e)N (number of theoretical plates)

[5] 2. DO EITHER

A 1.00 µg sample of pure 226Ra is found to emit 3.7 x 104 particles per second. What is the half life of 226Ra? The atomic weight of radium is 226.0254. NA = 6.022 x 1023

An assay was done using thymidine-5’-triphosphate[32P]. It took a weekend (48 h) to count the set of samples. If no half-life correction was made, what would be the error in the countrate for the last sample as compared with the first one counted? The half-life for 32P is 14.28 days.

[5] 3. DO EITHER

Silver is to be deposited from a solution that is 0.150 M in , 0.320 M in KCN, and buffered to a pH of 10.00. Oxygen is evolved at the anode at a partial pressure of 1.00 atm. The cell has a resistance of 2.90 Ω; the temperature is 25C.

Ag(CN)2- + e-  Ag(s) + 2CN- Eo = -0.31 V

O2 + 4H+ + 4e- 2H2O Eo = +1.229 V

Calculate:

(a) the theoretical potential needed to initiate deposition of silver from this solution.

(b)the IR drop associated with a current of −0.12 A.

(c)the initial applied potential, given that the O2 overvoltage is 0.80 V.

A solution is 0.0500 M in BiO+ and 0.0400 M in Co2+ and has a pH of 2.50.

BiO+ + 2H+ + 3e- Bi(s) + H2OEo = +0.320 V

Co2+ + 2e- Co(s)Eo = -0.277 V

(a)What is the concentration of the more readily reduced cation at the onset of deposition of the less reducible one?

(b)What is the potential of the cathode when the concentration of the more easily reduced species is 1.00  10−6 M?

[6] 4.Using masss spectrometry, we wish to distinguish between propene (C3 H6) and diazomethane (CH2N2). The mass spectrum obtained of one of these compounds had a peak at 42 with an intensity of 78.0 and a peak at 43 with an intensity of 2.6. Which compound was this?

What would we expect the ratio of the (M+1) to M peak to be for the second compound?

Relative abundance of 2H is 0.016 %

Relative abundance of 13C is 1.08 %

Relative abundance of 15N is 0.38 %

Explain the origin of the following peaks in the mass spectrum of 2-octanone.

128

113

Show where the molecule is cleaved to produce each fragment.