Exam 2019, questions PDF

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Semester One Examination Period Faculty of Science EXAM CODES:

CHM1011 – Mock Exam # 1

TITLE OF PAPER:

CHEMISTRY I

EXAM DURATION:

2 hours writing time

READING TIME:

10 minutes

THIS PAPER IS FOR STUDENTS STUDYING AT: (tick where applicable)  Berwick X Clayton  Malaysia  Off Campus Learning  Caulfield  Gippsland  Peninsula X Monash Extension  Parkville  Other (specify)

 Open Learning  Sth Africa

During an exam, you must not have in your possession any item/material that has not been authorised for your exam. This includes books, notes, paper, electronic device/s, mobile phone, smart watch/device, calculator, pencil case, or writing on any part of your body. Any authorised items are listed below. Items/materials on your desk, chair, in your clothing or otherwise on your person will be deemed to be in your possession. No examination materials are to be removed from the room. This includes retaining, copying, memorising or noting down content of exam material for personal use or to share with any other person by any means following your exam. Failure to comply with the above instructions, or attempting to cheat or cheating in an exam is a discipline offence under Part 7 of the Monash University (Council) Regulations.

AUTHORISED MATERIALS  YES

OPEN BOOK

X NO

CALCULATORS X YES  NO * Calculators with School of Chemistry/Faculty of Science authorization label only SPECIFICALLY PERMITTED ITEMS X YES  NO if yes, items permitted are: *Molecular Modelling Kits

Candidates must complete this section if required to write answers within this paper

STUDENT ID:

__ __ __ __ __ __ __ __

DESK NUMBER:

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Data Page Useful equations

Physical constants

Wave equation:

c = 

Einstein equation:

E = h

Rydberg equation:

1

𝜆

=

c = 2.998 x 108 ms-1

1 𝑅(𝑛 2 𝑎

−

h = 6.626 x 10-34 J.s

1 ) 𝑛𝑏2

R = 1.097 x 107 m-1

Bond order = 1(# bonding electrons - # anti-bonding electrons) 2

NA = 6.022  1023

Gases R = 8.314 J/K/mol = 0.08206 atm·L/mol·K

Ideal Gas Equation: pV = nRT Non-Ideal Gas Equation: (𝑝 +

𝑛2 𝑎 𝑉2

)(𝑉 − 𝑛𝑏) = nRT

Total Pressure =  Partial Pressures of Component Gases

1 bar = 1.0 x 105 Pa

Thermodynamics ΔU = q + w

G  = H  – T  S

w = -p V

Go = -RTlnK

q = mc T

G = G  + RT ln Q

Kw at 25 oC = 1.0 x 10-14 0 oC = 273.15 K

Equilibria Henderson-Hasselbach: pH = pKa + log

[base] [acid]

E°cell = E°red - E°ox

Kinetics Zero-order reaction: [A]t = [A]o - kt First-order reaction: [A]t = [A]oexp(-kt) Second-order reaction (only one reactant A): Half-life: t1/2 = 0.693/k Arrhenius equation: k = Ae-Ea/RT −𝐸𝑎 1 1 𝑘2 ( − ) ln ( ) = 𝑘1 𝑅 𝑇2 𝑇1

1 atm = 1.013 x 105 Pa

1

[𝐴]𝑡

1

− [𝐴] = 𝑘𝑡 0

Question 1 (1 + 2 + 3 + 2 + 4 + 3 + 3 + 2 + 2 + 4 + 5 + 9 = 40 marks) Nitrogen required for fertilizer is massed produced using the Haber-Bosch process, where nitrogen gas, N2, and hydrogen gas, H2, react together to form ammonia, NH3. The following questions are related to the molecules in this reaction. a) Write out the full electronic configuration of N.

b) Explain why the diagram below of the valence electronic configuration of nitrogen does not exist.

c) What are the names of the following orbitals? a) b)

c)

d) The ionisation energy of the nitrogen atom is 1402 kJ mol-1 whereas phosphorus is 1011 kJ mol-1. Explain why.

e) The nitrogen atom will have an empty n = 3 energy level. i) What are all the values for the angular momentum quantum number, l?

ii) What are the values of ms?

Question 1 continued f) The nitrogen atom will also have an empty 4s orbital. i)

Draw the electron density plot for the 4s orbital using the axes below.

ii) How many nodes will a 4s orbital have?

g) Nitrogen gas contains a triple bond whereas hydrogen gas has a single bond. i) Will nitrogen gas have a larger, smaller or the same bond energy as hydrogen gas?

ii) What are the two factors that determine the bond energies of homonuclear diatomic molecules?

h) Write out the full balanced equation for the Haber-Bosch process.

i) The reaction of the Haber-Bosch process requires a catalyst of iron with traces of aluminium oxide and potassium oxide. Write out the molecular formula for: - aluminium oxide

- potassium oxide

Question 1 continued j) Ammonia contains hydrogen atoms as well as nitrogen. i) An electronic transition in a hydrogen atom from the ground state (n = 1) occurs through absorption of 1.937  10-18 J of energy as electromagnetic radiation. Determine the frequency of the photon that was absorbed by the hydrogen atom.

ii) Calculate the new energy level (n) of the electron.

k) The following questions are specifically for ammonia, NH3. i) Draw the Lewis structure for ammonia.

ii) What is the parent geometry of ammonia? iii) What is the molecular geometry of ammonia? iv) Does ammonia have a dipole? Yes

No

Question 1 continued l) Nitrogen fertilizer is normally sold as ammonium nitrate, NH4NO3. The nitrate ion structure is below. Sketch the valence bond diagram of nitrate, using one of the resonance structures shown. Make sure you include all the orbitals and labels.

Question 2 (1 + 1 + 1 + 6 + 1 = 10 marks) In the 1960s, the space scientists of the USA and the USSR both considered using elemental fluorine (F2) as a possible rocket propellant because of the higher specific impulse generated when fluorine replaced oxygen in combustion. Eventually these studies were halted due to handling problems with the gas, and the toxicity of the side-product from its combustion, hydrogen fluoride (HF). The following questions pertain to this homonuclear diatomic molecule. (a) In Molecular Orbital Theory, what names are given to the two molecular orbitals formed by the overlap of two s atomic orbitals?

(b) How does the energy of these two molecular orbitals compare to the energy of the s atomic orbital used to form them?

(c) What types of molecular orbitals may be formed by the overlap of two 2px atomic orbitals?

Question 2 continued (d) Draw the MO diagram for F2. Include all necessary labels, and arrows to indicate the electrons.

(e) What is the bond order for the F2 molecule?

Question 3 (5 + 2 = 7 marks) a) A mixture of cyclopropane gas, C3H6, and oxygen, O2, in a 1.00 : 4.00 mole ratio is used as an anaesthetic. What mass of each of these gases is present in a 2.00 L container at 23.5 °C if the total pressure is 1.00 × 105 Pa?

b) Strong hydrogen bonding is observed for both hydrogen fluoride, HF, and water, H2O. This is ultimately due to the large difference between the electronegativity of hydrogen (2.1) and fluorine (4.0) and oxygen (3.5). When comparing the hydrogen bonds for the two dimers in the figure below, which would you expect to exhibit the strongest hydrogen bond. Explain.

Question 4 (4 + 2 + 2 = 8 marks) The combustion of propane (equation below) is spontaneous. C3H8 (l) + 7 O2 (g) → 3 CO2 (g) + 8 H2O (g) a) Explain the spontaneity of this reaction in terms of the predicted signs and magnitudes of its reaction enthalpy, entropy and the resultant Gibbs Free Energy, with reference to the second law of thermodynamics and system and surroundings.

b) Give the measurement conditions (for example constant volume, constant pressure, constant temperature etc.) which should be used to measure the enthalpy change,  H, for the combustion as well as the apparatus to use for the measurement.

c) Mark the following statements as true or false: i. In a closed system, work energy may be transferred from the system to the surroundings.

ii.

A reaction was carried out in a frictionless piston. The piston block was pushed out as the reaction proceeded. The system has gained internal energy.

d) Write the first law of thermodynamics as a statement.

Question 5 (2 + 4 + 1 = 7 marks) Aluminum foil reacts vigorously with chlorine gas to give solid aluminum trichloride. The standard enthalpies of formation and standard molar entropies of the materials involved are shown below:

2 Al(s) + 3 Cl2(g)  2 AlCl3(s) Substance

S0 (J mol-1 K-1)

ΔHf0 (kJ mol-1)

Al(s)

28.30

0.000

Cl2(g)

223.1

0.000

AlCl3(s)

109.3

-705.6

a) Did the entropy of the system increase or decrease during the reaction? Justify your answer.

b) Calculate the standard Gibbs free energy, ΔG0 for the reaction, assuming that it occurs at 25.0°C:

c) State whether this reaction would be spontaneous or not at 25.0°C. Justify your answer.

Question 6 (4 marks) a) A so called ‘coffee cup’ calorimeter is used to determine the energy released when a strong acid and a strong base are mixed together. In this experiment, 200 mL 2.00 M HCl and 300 mL 2.00 M NaOH are combined, and the temperature of the solution is measured to increase from 5.00° C to 15.5 °C. Assuming that no heat is lost to the calorimeter itself, and that the density of the solution is 1.00 g/mL, determine the enthalpy of neutralization. Assume the heat capacity of the solution is 4.184 JK-1g-1.

Question 7 (3 + 2 = 5 marks) a) The Ksp for lead(II) chloride is 1.70 × 10-5. If you place 0.0108 mol of this solid in 100 mL water, how much solid will be left after the system reaches equilibrium?

b) If the lead(II) chloride was dissolved in 0.500 M HCl solution would there be more or less solid left? Explain your answer using supporting calculations.

Question 8 (2 + 2 + 1 = 6 marks) The value for the pKa acetic acid = 4.74. a) Determine Kb for the dissolution of the acetate ion in water. Assume the temperature is 25.0°C.

b) What is the pH of a buffer solution made up of 0.240 M sodium acetate and 0.260 M acetic acid?

c) To prepare a buffer solution which is more resistant to a change in pH, should the concentration of sodium acetate be increased or decreased?

Question 9 (1 + 1 + 1 + 4 = 7 marks) a) The values of E° are based on which standard electrode?

b) If an element is undergoing oxidation, are they gaining or losing electrons?

c) What is the function of a salt bridge in galvanic and electrolytic cells?

d) A galvanic cell is created from the two half cells in the table below. Half Reaction MnO4 (aq) + 8H + 5e- ⇌ Mn2+ (aq) + 4H2O(l) Ag+ (aq) + e- ⇌ Ag (s) -

+

i) Which chemical species is the oxidant?

ii) Write out the balanced chemical reaction.

iii) Determine the cell potential in volts.

E° (V) +1.51 +0.80

Question 10 (1 + 2 + 3 + 2 = 8 marks) Use the information below to answer the following questions: CO(g) + H2O (g) ⇌ CO2 (g) + H2 (g)

Kc = 31.4 at 588 K

H = -41.1 kJ/mol

a) Write out the equilibrium expression, Kc

b) If a 10.00 L vessel has 2.50 mol CO and H2O, and 5.00 mol CO2 and H2 gas at 588 K, determine the reaction quotient, Qc.

c) What are the concentrations of all species when the vessel in b) comes to equilibrium?

d) If this reaction is cooled down, determine whether the concentration of reactants increases or decreases. Justify your answer.

Question 11 (2 + 4 = 6 marks) Radioactive isotopes of iodine are used as imaging and therapeutic agents. The isotope 123I has a half-life, t½, for radioactive decay of 13.22 hours. a) Calculate the rate constant, k, for the radioactive decay of 123I (remember to include units for k in your answer).

b) A radiation detecting device is used to measure the amount of iodine that has collected in the thyroid gland of a hospital patient. At 9 am on a Monday morning, this device measures 3500 counts. Predict the number of counts that would be measured 24.00 hrs later. Justify your answer.

Question 12 (2 + 2 + 3 + 2 = 9 marks) A reaction has a rate law, Rate = k[A]2, with a rate constant, k = 5.08 × 104 L mol-1 s-1 at 25.0 C. a) Sketch the general shape of a graph plotting [A] (y-axis) against time (x-axis). Your sketch does not need to be to scale.

b) At the beginning of the reaction, the initial concentration of A is 0.150 mol L-1. What is the concentration of A at t = 3 milliseconds?

c) The rate constant for this reaction was found to be k = 7.32 × 104 L mol-1 s-1 at a temperature of 100 C. Using this, together with the above rate constant and temperature, calculate the activation energy for this reaction.

d) Why is the rate constant greater at a higher temperature?

Question 13 (4 marks) The kinetics of the following dimerisation reaction can be studied by spectrophotometry, since the reactant molecule is coloured, but the product is not. A spectrophotometer is used to measure how much light is absorbed by the sample, and as this decreases, it can be interpreted as the decrease in the concentration of the reactant.

The tabulated data below shows the change in concentration of the monomer (reactant) over time. Additional columns have been included for ln[monomer] and 1/[monomer]. Time (min) 0 5 10 15 20

[monomer]

ln[monomer]

1/[monomer]

1.2 1.1 1 0.89 0.81

0.182 0.095 0.000 -0.117 -0.211

0.83 0.91 1.00 1.12 1.23

Time (min) 25 35 45 55 65

[monomer]

ln[monomer]

1/[monomer]

0.77 0.67 0.59 0.54 0.48

-0.261 -0.400 -0.528 -0.616 -0.734

1.30 1.49 1.69 1.85 2.08

Using the data above, determine whether the kinetics for this reaction is zero, first, or second order.

END OF PAPER...