1st round problems final v2 - Ķīmijas didaktikas …1/c with latt, c = 7.8695 late the vol rite...
TRANSCRIPT
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www.biosan.lv
1ST ROUND, PROBLEMS
Solve all or some of the four problems given on the next pages and write your answers in MS Excel answer sheets provided. If there are some explanations required, write them in English or Russian. Please, send your answers to: [email protected] till 29.10.2009. at 24:00. Answers which will be sent after this time will not be graded. Write all the answers in one workbook but in different worksheets for each problem. You should fill in the green spaces provided.
File name must consist from your name, surname (in English) and country, for example John_Black_England.xls (or *.xlsx). If you do not name the file as described you will receive 3 point penalty. For all correctly solved problems you can get the maximum of 30 points. The exact amount of points for each task is given at the top of each problem.
All students who will be taking part in at least one round will participate in the final round which will be held on the web on 27th of February. During the final round you will have to solve the multiple choice test. Authors for problems in this round:
Kaspars Veldre Vladislav Ivaništšev Bernardas Morkunas
PhD student, University of Latvia, Department
of Chemistry
PhD student, Tartu University, Institute
of Chemistry
3rd year student, Cambridge University
Karina Kizjakina Agris Bērziņš Aurimas Vysniauskas PhD student,
Virginia Polytechnic Institute and State
University, Department of Chemistry
MS student, University of Latvia, Department of
Chemistry
Student, Oxford University
Good luck with problem solving! ☺
If you have any questions, address them to us in English and send them to: [email protected] Feel free to ask!
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Problem 1 (Lithuania)
Self destructing paper (6 points)
Old books are a very important cultural heritage of nation’s
history. USA is losing this treasure, soon 40% of the books will be
too fragile to handle. Problem of this fact hides in the paper of
these books. In XIX century paper manufacturers found it useful
to add Al2(SO4)3 into paper in the manufacturing process but,
unfortunately, this compound causes self destruction of the
paper due to the formation of Al(OH)2+ ions during the hydrolysis reaction.
a) Al(OH)2+ also forms in aqueous Al(NO3)3 solution. Ionization degree of this hydrated ion is
52.9% and pH of this solution is 5.00. Calculate pKa of this ion.
b) One page of a book made from paper manufactured using Al2(SO4)3 contains 0.86 mg of it.
Book of 500 pages was dipped into 5.0 L volume of water and all alum dissolved. 1.0 ml of this
solution was taken and pipetted into 1.0 L flask filled with distilled water. Calculate
concentrations of all ions present in the resulting solution.
c) What compound causes destruction of the paper? Propose possible way to prevent
destruction.
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Jadarite Hydrated copper uranyl phosphate
There is a real mineral what is green and radioactive. Its chemical composition is: Cu(UO2)2(PO4)2∙(8‐12)H2O (hydrated copper uranyl phosphate).
On the right side of the page the decay chain of uranium‐238 (main isotope of natural uranium) is shown.
Assume, that process 238U → 234U is one step process with the
rate constant the same as for 238U → 234Th. In natural uranium nowadays the abundance of isotopes is 238U – 99.2742%, 235U – 0.7204% and 234U – 0.0054%.
8. Write down all the reactions and classify them by the type of decay (alpha, beta or gamma).
Alchemist Daniel Rebuss took 5.00 g of Cu(UO2)2(PO4)2∙(8‐12)H2O (hydrated copper uranyl phosphate) and determined that it loses 20.6% of mass by heating. Let’s assign amount of uranium atoms in this ore with N0.
9. Calculate N0.
10. Construct the graph to show how the amounts of 238U, 234U, 230Th, 226Ra and 222Rn in this sample will change during the next million years.
For your calculations you can use computer program “Kinet” from IChO 2007 (Moscow, Russia), program “Kinetics” (available in http://lu.lv/skoleniem/kim/konkurss/2009/, created by Mihails Arhangeļskis) or create your own calculation spreadsheet, for example, in MS Excel. Graphs can be saved as screenshots (use Print Screen button).
11. Find the time tmax1, when there is maximum number of 230Th atoms in the sample of Daniel Rebuss.
Now, assume that you have pure 234U isotope. In situations like this tone can use equations given below for calculation of the amount of particles in left (?) time:
And its derivative:
12. Using formulas given above calculate the time tmax2, when there is the maximum number of 230Th atoms in the sample.
13. Explain the differences between tmax1 and tmax2!
Scientific references 1. P. S. Whitfield, Y. Le Page, J. D. Grice, C. J. Stanley et.al. LiNaSiB3O7(OH) ‐ novel structure of the new borosilicate
mineral jadarite determined from laboratory powder diffraction data, Acta Cryst. (2007). B63, 396‐401 2. Web page: mindat.org ‐ the mineral and locality database Available online: http://www.mindat.org/min‐
31570.html [07.07.2009.],Copyright Jolyon Ralph and Ida Chau 1993‐2009
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Problem 3 (Lithuania)
Push those arrows (8 points)
The study of the mechanisms of reactions in the modern organic chemistry is a field of a great scientific interest. In this problem you will have an opportunity to show your skills in predicting mechanisms of simple (and not so simple) organic and bioorganic reactions.
At first, let us explore a very handy reaction discovered by Charles Friedel and James Crafts in 1877.
1. Provide a detailed mechanism for Friedel‐Crafts alkylation.
However, the Friedel‐Crafts alkylation is usually replaced by Friedel‐Crafts acylation.
2. Provide a detailed mechanism for Friedel‐Crafts acylation.
3. Predict the reagents for synthesis of the Product 1 using Friedel‐Crafts alkylation reaction. Predict the
major products of this reaction along with mechanisms of their formation.
That is it for the easy part. ☺
4. Provide a detailed mechanism for the formation of 1,2,3,4,5,6‐hexahydropentalene
Feeling bored already? Well, you should. Now, let us explore a basic bioorganic reaction. ☺
5. Provide a plausible mechanism for the formation of a cyclic triterpene and spot the terpene subunits in the starting compound and the product. (Hint: ‐OPP group acts as a leaving group during the first step)
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Problem
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