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2007 Chemistry Exam 2 Written Examination

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asa.hoshi:
SECTION B - Short answer questions
Question 3
The arrangements of electrons in atoms and ions are often written in simplified form, known as 'condensed electron configuration'. For example,. the condensed electron configuration of beryllium is written as
[He]2s2
where [He[ stands for the electron configuration of helium (1s2), which is the noble gas element previous to beryllium in the periodic table.
a. Write condensed electron configuration for the following atoms and ions.
i. C
ii. Fe
iii. Fe2+

1 + 1 + 1 = 3 marks

b. State the group and period of the periodic table where an element with the electron configuration [Kr]4d10 5s2 5p4 is found.
Group:___ Period:___

1 mark

Total 4 marks

golids:
much appreciated asa :D

asa.hoshi:
SECTION B - Short answer questions
Question 8
Faraday's constant is defined as the charge on one mole of electrons. The value of Faraday's constant can be determined experimentally by electrolysis using inert electrodes.
A current of 1.62 A is passed through a solution of copper (II) nitrate for 581 s. At the end of that time, the copper deposited at the negative electrode was collected. Its mass was found to be 0.306g.
a. Write an equation for the half reaction occurring at the negative electrode of this electrolytic cell.
1 mark
b. Use the experimental data given above to calculate, to an appropriate number of significant figures, the
-> charge, in coulombs, that was passed through the electrolytic cell
-> amount, in mol, of copper deposited at the negative electrode.
3 marks
c. Use the values obtained in part b. to calculate the experimentally determined value of Faraday's constant.
d. The value of Faraday's constant given in your data sheet is 96500 C mol-1. The experiment above was repeated and a value for Faraday's constant was found to be 98400 C mol-1. The amount of charge passed is accurately known. Described one possible source of experimental error which would result in obtaining an experimental value that was higher than the one given in the data sheet.
1 mark

Total 7 marks

asa.hoshi:
ok my hands are tired after 1 hour of typing this crap. I seriously don't care about CHEMISTRY anymore! but i do care about FSN! That's why I spent 1 hour of my time typing this instead of resting.

Anyway, that's all I'm typing for today. I might be able to take photos of it tonight when I get my camera back. Gotta rest and study for exams. Bye!

asa.hoshi:
SECTION B - Short answer questions
Question 6
Ethanol (C2H5OH) is a common fuel burnt in some lightweight, compact stoves suitable for use when hiking.
[picture of cooking pot, fuel, stove]
a. Consider the following information
-ethanol burns in excess air according to the following equation.
C2H5OH (l) + 3O2 (g) --> 2CO2 (g) + 3H2O(g) DeltaH = -1364 kJ mol-1
-The cooking pot is made from aluminiym and has a mass of 150g.
-The specific heat capacity of aluminum is 0.900 Jg-1C-1.
-The specific heat capacity of water is 4.18 Jg-1C-1.
i. Calculate the minimum amount of energy, in kJ, required to heat 550g of water and the pt from 18.5C to 100.0C
iiCalculate the mass, in g, of ethanol that needs to be completely burnt to provide this energy.
iii Only 35% of the energy released by the combustion of ethanol is transferred to the cooking pot and contents. Calculate the mass, in g, of ethanol that needs to be burnt in practice to heat the water and pot from 18.5C to 100.0C.
2 + 2 + 1 = 5 marks
b. Other camping stoves use butane (C4H10) as fuel. Given that, on complete combustion, 6.00g of butane releases the same amount as 10.0g of ethanol, calculate the magnitude of deltaH, in kJ mol-1, for the reaction
2C4H10 (g) + 13O2 (g) --> 8CO(g) + 10H2O (g)
2 marks

Total 7 marks

NO more typing... lol

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