2007 Chemistry Exam 2 Written Examination

[asa.hoshi]

CHEMISTRY
Written examination 2
Thursday 15 November 2007

SECTION A - Multiple-choice question
Question 1
IN which one of the following compounds does the transition metal display the lowest oxidation state?
A. CrO3
B. Cu2S
C. MnCl2
D. K2Cr2O7

Question 2
Consider the following nuclear reaction that takes place in stars.
8\4Be + 4\2He  --> 12\6C
Which of the following statements about this change is/are correct?
I. The reaction is endothermic
II. The mass of the 12\6 nucleus is greater than the combined masses of the reactants.
A. I only
B. II only
C. both I and II
D. neither I nor II

Question 3
Some information about the element rhenium (Re) is given in the table below.
Isotope            Relative isotopic mass
185Re                          185.0
187Re                          187.0
Given that the relative atomic mass of Re is 186.2, the percentage abundance of 187Re is closest to
A. 40
B. 50
C. 60
D. 70

Question 4
A solution prepared by stirring Na2O(s) in water undergoes an acid-base reaction with a solution prepared from SO3(g) and water.
Which one of the following salts could be isolated from the reaction mixture?
A. Na2S
B. NaHSO3
C. Na2SO3
D. Na2SO4

Question 5
Which one of the following alternatives contains molecules and ions that are all likely to form a complex ion with a transition metal cation.
A. Cl-, F-, CN-, H+
B. NH3, Cl-, F-, H20
C. Na+, CN-, F-, H20
D. CH4, Cl-, NH3, H20

Question 6
Predict which one of the following compounds would be coloured.
A. BaSO4
B. AlPO4
C. KClO4
D. NaMnO4

Question 7
Which of the following statements about enzymes are correct?
I. Enzymes are proteins.
II. Enzymes increase the rate of biochemical reactions.
III. Enzymes increase the equilibrium constant of biochemical reactions.
A. I and II only
B. I and III only
C. II and III only
D. I, II and III

Question 8
A structure of Vitamin C is given below:

Vitamin C is an important biological molecule. It is often added to foods as an antioxidant. Based on this information, and on the structure of Vitamin C shown above, it can be predicted that vitamin C is more soluble in
A. fats than in water and is a good oxidant
B. fats than in water and is a good reductant
C. water than in fats and is a good oxidant
D. water than in fats and is a good reductant

Question 9
The types of compounds that comprised the major food groups include carbohydrates, fats and proteins. A sample, containing only one of these three types of compounds, is analyzed and found to contain the following
Carbon: 76.2%
Oxygen: 11.3%
Nitrogen: 0%
The compound
A. is likely to be a fat
B. is likely to be a protein
C. is likely to be a carbohydrate
D. cannot be identified as the percentage composition of other elements has not been given.

Question 10
The follow two unbalanced equations represent process which are part of the nitrogen cycle.
I. NH3 (aq) --> NH4+ (aq)
II. NH4+ (aq) --> NO3-(aq)
Which one of the following alternatives correctly describes the reactants in each of these processes?
   In process I, NH3(aq) is... In process II, the NH4+(aq) ion is
A. an acid...reduced
B. a base...reduced
C. an acid...oxidised
D. a base...oxidised

[gfb]

Thanks asa.hoshi  :wink:  Now lets wait for Coblin's answers

[asa.hoshi]

Question 11
Consider the following half cells which are set up under standard conditions.
Half Cell - electrode - electrolyte
I - metal A - A2+ (aq)
II - platinum - B2+(aq) and B3+ (aq)
III - metal C - C+ (aq)
-> When a galvanic cell is constructed from half cell I and half cell II, the electrode in half cell II is negative.
-> When a galvanic cell is constructed from half cell II and half cell III, the electrode in half cell III is negative.
The strongest oxidant is
A. A2+ (aq)
B. B2+(aq)
C. B3+ (aq)
D. C+ (aq)

Questions 12, 13, 14 refer to the following information.
The diagram below represents a diaphragm cell used for the commercial production of chlorine gas.
at the +ve section - brine is inserted and X comes out
at the -ve section - Y and sodium hydroxide solutions comes out
middle - porous diaphragm
Question 12
The gases labelled X and Y are
  X...Y
A. chlorine... oxygen
B. oxygen...chlorine
C. chlorine...hydrogen
D. hydrogen...chlorine

Question 13
On function of the porous diaphragm in the cell is to
A. act as a catalyst to increase the rate of reaction
B. allow movement of ions between the cell compartments
C. prevent sodium ions from entering the solution near the anode
D. prevent the electrolyte from making contact with the gases produced.

Question 14
A highly concentrated salt solution, called brine, is used as the electrolyte in this cell.
The main reason that a highly concentrated, rather than a diluted, solution is used is in order to
A. allow an electric current to pass through the cell.
B. produce chlorine gas, in preference to oxygen gas.
C. allow sodium hydroxide to be separated from the salt by crystallization.
D. create non-standard conditions that ensure hydrogen gas production.

A rechargeable cell, used in laptop computers, contains a metal alloy (designated M) which has hydrogen atoms adsorbed on its surface, and nickel in the form of NiO(OH)(s) and Ni(OH)2(s),
The half reactions, written as reduction reactions, are
H2O(l) + e- <--> H (adsorbed on M) +OH-(aq)
NiO(OH)(s) + H2O(l) + e- <--> Ni(OH)2(s) + OH-(aq)
Question 15
When this cell is generating electricity
A. NiO(OH) acts as the oxidant
B. the concentration of OH-ions in the cell increases as the cell discharges
C. OH- ions produced at the negative electrode migrate to the positive electrode.
D. electrons flow in the external circuit from the positive to the negative electrode.

Question 16
When the cell is recharged, which one of the following precesses occurs at the electrode connected to the positive terminal of the external power source?
A. reduction of H2O(l)
B. reduction of NiO(OH)(s)
C. oxidation of Ni(OH)2(s)
D. oxidation of H (adsorbed on M)

Question 17
A fuel cell currently under development for powering small electronic devices is based on the reaction of methanol and oxygen using an acidic electrolyte.
The reductant in the cell reaction and the half reaction at the anode are
  reductant...anode reaction
A. methanol... O2(g) + 4H+(aq) v+ 4e- --> 2H2O(l)
B. oxygen... O2(g) + 4H+(aq) v+ 4e- --> 2H2O(l)
C. methanol... CH3OH(g) + H2O(l) --> CO2(g) + 6H+(aq) + 6e-
D. oxygen... CH3OH(g) + H2O(l) --> CO2(g) + 6H+(aq) + 6e-

Questions 18, 19 refer to the following information.
A chemist used bomb calorimetry to measure the enthalpy change (delta H) for the combustion of butane.
Question 18
The calibration factor (CF) of the calorimeter was determined by measuring the temperature rise (delta T1) that occurred when a known amount of charge (Q) was passed through the heating element in the calorimeter at a measured voltage (V).
The CF in JC-1 is
A. Q/[V x delta T1]
B. delta T1/[Q x V]
C. Q x V x delta T1
D. [VxQ]/[delta T1]

Question 19
In the calorimeter (calibration factor, CF), n mol of butane was then burnt and the resulting temperature rise (delta T2) was measured.
The deltaH, in Jmol-1, for the reaction
2C4H10(g) + 13O2(g) --> 8CO(g) + 10H2O(l)
is
A. 2 x CF x deltaT2 x n
B. [2 x CF x deltaT2] / n
C. [CF x deltaT2] / [2 x n]
D. [CF x deltaT2] / [n]

Question 20
During the production of electricity in a coal-fired power station, energy is present in the following forms.
I. mechanical energy of turbine.
II. chemical energy of coal and oxygen.
III. thermal energy of steam.

The amount of energy in each of these forms that take part in the generation of a fixed quantity of electricity is, from lowest to highest
A. III, I, II
B. I, II, III
C. I, III, II
D. II, III, I

END OF SECTION A

[asa.hoshi]

SECTION B - Short answer questions
Question 1
Refer to the periodic table in the data sheet when answering this question.
Identify each of the following elements on the basis of the properties listed in the table below. Write its chemical symbol in the appropriate box in the third column.
Property...chemical symbol of the element
i. The element which forms an ion with electron configuration if 1s 2s2 2p6 and a charge of 2+
ii. The third member of the actinides
iii. A period 3 element which forms an ionic oxide that reacts with both acids and bases.
iv. In the ground state, atoms of this element have electrons in 2 shells and the first four ionization energies are 0.80, 2.43, 3.66 and 25.02 MJ mol-1
v. A element that is more electronegative that chlorine and its atoms have an outer-shell configuration of s2p4
vi. An element which is more metallic that germanium (Z=32), has a higher first ionization energy than bismuth (Z=83) and atoms with an outer-shell configuration of s2p2.

Total 6 marks

[asa.hoshi]

SECTION B - Short answer questions
Question 2
The work of many scientists has contributed to an understanding of atomic structure. As a result of their work, previously unknown elements have been discovered and the search for new elements continues today.
a. Dimitri Mendeleev (1834-1907) is usually given much of the credit for systematically arranging the elements into a periodic table. Briefly describe two important features of the table he created.
2 marks

b. The discovery of element 113 was claimed by teams of Russian and American scientists in February 2004. Following international conventions, it has initially been given the name ununtrium and the symbol Uut, before a permanent name and symbol are given to it.
Uut undergoes rapid radioactive decay but atoms of Uut have been identified with a mass number of 283 and also with a mass number of 284.
i. Name an instrument that could be used to determine the mass numbers of different isotopes of an element.
ii. State the number of subatomic particles in an uncharged Uut atom of mass number 284.
Protons:___ Electrons:___ Neutrons:___
iii. In what group and period is Uut located in the periodic table?
Group:___ Period:___
iv. Given the symbol of the element that is expected to be most similar to Uut in chemical properties.
v. In terms of atomic structure, explain why the atomic radius of Uut is predicted to be smaller than that of Fr (Z=87).
vi. In terms of atomic structure, explain why the the first ionisation energy of Uut is predicted to be smaller than that of Al (Z=13).
vii. Atoms of Uut with a mass number of 283 undergo radioactive decay into two particles, one of which is an alpha-particle (a helium nucleus). Write a balanced equation for this nuclear reaction.

1 + 1 + 2 + 1 + 1 + 1 + 1 = 8 marks

Total 10 marks

[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

[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

[kingmar]

Asa.hoshi, you GOD.

Good job!! FSN appluads your dedication. Better rest those wrists... you do have more exams, right?

[rhcpfox1]

Top work asa.

Quality.

[Collin Li]

Thanks heaps asa.

I've been fixing your errors. Can someone check Question 4. I think I've fixed it, but I may have option C incorrect (because I haven't seen the question).

[asa.hoshi]

Asa.hoshi, you GOD.

Good job!! FSN appluads your dedication. Better rest those wrists... you do have more exams, right?

got 2 big ones left. spesh and jap

[kingmar]

Good luck for those. No doubt coblin wants a piece of Spesh.

By the way, coblin, it doesn't matter what option C was, because it's incorrect regardless.