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Cork Institute of Technology
Bachelor of Engineering (Honours) in Electronic Engineering – Stage 1
(Bachelor of Engineering in Electronic Engineering – Stage 1)
(NFQ – Level 8)
Summer 2005
Materials Science
(Time: 3 Hours)
Instructions Answer FIVE questions. All questions carry equal marks.
Examiners: Dr. R. Hourihane Prof. C. Burkley Mr. J. Ryan
Q1. (a) (i) Describe an experiment conducted by Thomson and co-workers which led to the discovery of the first sub atomic particle, the electron. A diagram is required and may aid your description. (5 marks) (ii) Name the experiment which proved the existence of the proton. (2 marks)
(b) (i) Distinguish between atomic number and mass number. Give an example of each, picking an element from the periodic table. (2 marks) (ii) The mass spectrometer is a very useful instrument with many important applications, among which are the determination of relative isotopic masses and abundances of isotopes.
- Explain the underlined terms
- Outline how the mass spectrometer works (7 marks)
(c) Determine the relative atomic mass of silver Ag, correct to two decimal places, given that natural occurring silver consists of 51.84% 107 Ag with an isotopic mass of 106.905 and 48.16% 109 Ag with an isotopic mass of 108.905.^ (4 marks)
Q2. (a) Define: (i) atomic radius (ii) ionisation potential (iii) electron affinity (6 marks)
(b) How do each of the quantities in (a) vary across a period and down a group of the periodic table? (4 marks) Contd…/
(c) Using the periodic table, arrange each set of atoms in order of increasing atomic radius. (i) Ca, Mg, Be (ii) Ga, Br, Ge (iii) Si, Ti, Al. (6 marks)
(d) The electron affinity of lithium (Li) is a negative value, whereas that of beryllium (Be) is a positive value. Use electron configuration to account for this observation. (4 marks)
Q3. (a) Draw the Lewis structures and determine the shape of each of the following: (i) PCl 3 , (ii) Na 2 O, (iii) NO+^ (8 marks)
(b) Describe the “electron sea” model of metallic bonding. How does it account for the metallic properties: (i) electrical and thermal conductivity. (ii) metallic lustre. (6 marks)
(c) (i) Outline how crystalline solids differ from amorphous solids. (ii) Metallic crystals pack by either hexagonal close packing or cubic close packing. Distinguish between the two. Diagrams required. (iii) Magnesium is described as AB hexagonal close packed, whereas copper is described as ABC close packed. Explain. (6 marks)
Q4. (a) (i) Explain the term ‘chemical kinetics’. (ii) List three quantities which influence the rate of a chemical reaction. (5 marks)
(b) At elevated temperatures, nitrogen dioxide decomposes to nitric oxide and molecular oxygen. 2 NO 2 (^) ( g )→ 2 NO ( g )+ O 2 ( g )
From the concentration and time data (given next page) for this reaction at 300°C, (i) prove the reaction is second order (ii) evaluate a value for the specific rate constant (iii) give the units for the rate constant at this temperature
Q7. (a) (i) Explain the difference between Homogeneous and Heterogeneous Equilibrium. (3 marks) (ii) Consider the following system:
PCl 5 (g) PCl 3 (g) + Cl 2 (g) ∆H = 87.9 kJ
If the reaction is at equilibrium, what would be the effect of: a. adding Cl 2 b. increasing the temperature on the system c. adding PCl 5 (g) (3 marks)
(b) Calculate the equilibrium constant (Kc) when the following reaction has reached equilibrium:
N 2 (g) + 3H 2 (g) 2NH 3 (g)
On analysis the mixture of gases was found to contain 0.1207 M H 2 , 0.0402 M N 2 and 0.00272 M NH 3. (6 marks)
(c) Sulphur trioxide decomposes at high temperature in a sealed container.
2SO 3 (g) 2SO 2 (g) + O 2 (g)
Initially the SO 3 (g) has a concentration of 6.09 x 10-3^ M. At equilibrium, the SO 3 (g) concentration is 2.44 x 10-3^ M. Calculate the value for Kc. (8 marks)
Q8. (a) A galvanic cell is based on the following half reactions: In +^ ( aq )→ In^3 +( aq )± 2 e^ − Br 2 (^) ( l )+ 2 e −^ → 2 Br −( aq ) (i) Label the reactions as anode or cathode processes. (ii) Using the table of standard reduction potentials attached, and that the standard e.m.f. for the cell is 1.46 V, calculate the reduction potential for In 3+^ to In + (6 marks) (b) Consider the galvanic cell that uses the following reaction: Cu ( s )+ 2 Fe^3 +^ ( aq )→ Cu^2 +( aq )+ 2 Fe^2 +( aq ) What is the potential of the cell at 25°C that has the following ion concentrations? [Fe3+] = 1 x 10-4^ mol dm- [Cu2+] = 0.25 mol dm- [Fe2+] = 0.20 mol dm-3^ (8 marks)
(c) Illustrate a galvanic cell containing the electrodes and electrolytes described by the cell reaction:
Zn(s) + Cu2+(aq) → Zn2+(aq)+Cu(s)
Your diagram should show the two compartments and a salt bridge. It should also show the direction in which the ions and electrons are moving. (6 marks)
