Cork Institute of Technology. Summer 2006 Materials Science (Time: 3 Hours)

Transcription

1 Cork Institute of Technology Bachelor of Engineering (Honours) in Electronic Engineering Stage 1 Instructions Attempt any FIVE Questions. All questions carry equal marks. (NFQ Level 8) Summer 2006 Materials Science (Time: 3 Hours) Examiners: Dr. R. Hourihane Prof. G. Hurley Dr. S. Foley Q1. (a) Sir J.J. Thomson, Ernest Rutherford and James Chadwick are three names associated with the modern structure of the atom. (i) Write a brief note describing the structure of the atom. Identify the contribution made by each of the gentlemen named above. (ii) Identify the subatomic particles by name, give the charge mass and location within the atom in each case. (i) Copper metal has two naturally occurring isotopes: Copper 63 (69.17%; isotopic mass 62.94amu) Copper 65 (30.83%; isotopic mass 64.93amu) Calculate the atomic mass of copper correct to two decimal places. (ii) Based on the above calculation, how many atoms of copper are there in a pure copper penny that weighs 2.15g. (1amu = x 0-24 g) (i) What are the four quantum numbers and what does each specify? (ii) Which of the following combinations of quantum numbers are not allowed? Explain your answers. a. n = 3, l = 0, m l = -1 b. n = 3, l = 1, m l = 1 c. n = 4, l= 4, m l = 0

2 Q2. (a) Distinguish between Ionic and covalent bonds, under the following headings. (i) definition (ii) groups in the periodic table most likely to be involved (iii) physical properties of compounds (melting points, boiling points solubility in water). Draw the Lewis Structure of each of the following: Mg; NaCl; NO + - ; BrO 3 Hence or otherwise, predict the shape of each species. (i) Identify three periodic properties which vary for elements in the periodic table. (ii) Show how each property varies across a period and down a group of the periodic table. Q3. (a) Write balanced nuclear equations for each of the following: (i) Beta emission from ruthenium 106 (Rn ) (ii) Alpha emission from bismuth 189 (Bi ) 204 (iii) Electron capture by polonium 204 (P o 84 ) Derive a mathematical expression for half-life (t½) from the integrated rate law. The half-life of radon 222, a radioactive gas of concern as a health hazard in some homes, is days. What is the decay constant of Ru 222? What percentage of C 14 6 (t½ = 5715 years) remains in a sample estimated to be 16,230 years old? 2

3 Q4. (a) What is the difference between internal energy change, E and enthalpy change, H? Which of the two is measured at constant pressure and which at constant volume? (5 marks) The following reaction describes how acetylene gas burns in oxygen, a reaction used in welding of metals: ( g) CO ( g) 5 C H ( g) + O2 ( g) H 2O + 2 H = kJ How much PV work is done (in kj) and what is the value of E (in kj) for the reaction of 6.50g (0.25 mol) of acetylene at atmospheric pressure if the volume change is 2.80L? (1L atm = 101.3J) (9 marks) The industrial degreasing solvent methlene chloride (CH 2 Cl 2 ) is prepared from methane by reaction with chlorine according to the following reaction CH 4 (g) + 2Cl 2 (g) CH 2 Cl 2 (g) + 2HCl (g) Using the following data calculate H o (in kj) for the reaction Hº/kJ CH 4 (g) + Cl 2 (g) CH 3 Cl(g) + HCl(g) CH 3 Cl(g) + Cl 2 (g) CH 2 Cl 2 (g) + HCl(g) -104 What law is being demonstrated by this calculation? 3

4 Q5. (a) The gas phase reaction of nitric oxide and bromine yields nitrosyl bromide 2NO(g) + Br 2 (g) 2NOBr(g) The rate law of the reaction is Rate = k[no] 2 [Br 2 ] What is the reaction order with respect to each of the reactants and what is the overall reaction order? (3 marks) At 600 o C, acetone (CH 3 COCH 3 ) decomposes to ketene (CH 2 = C = O) and various hydrocarbons. Given the initial rate data is the table. (i) Determine the rate law. (ii) Calculate the rate constant. (iii) Calculate the rate of decomposition when the acetone concentration is 1.8 x 10-3 M. Exp No. Initial [CH 3 COCH 3 ]/M Initial Rate of decomposition CH 3 COCH 3 /Ms x x x x 10-5 (i) Distinguish between homogeneous and a heterogeneous catalytic mechanisms, diagrams required. (ii) What effect does a catalyst have on the rate and mechanism of a chemical reaction? (3 marks) 4

5 Q6. (a) (i) For each of the following equilibrium write the equilibrium constant expression for Kc. 2S0 2 (g) + O 2 (g) 2SO 3 (g) Kc = 1.2 x HCl(g) H 2 (g) + Cl 2 (g) Kc = 2.0 x (ii) Does the equilibrium mixture contain mostly reactants or mostly products in each of the equations in (i) above. (4 marks) Methanol (CH 3 OH) is manufactured by the following reaction: catalyst CO(g) + 2H 2 (g) CH 3 OH(g) H o = -91kJ Does the amount of methanol increase, decrease or remain the same when (i) the temperature is increased (ii) the volume is decreased (iii) the catalyst is removed What will be the concentrations of each of the reactants & products after the equilibrium is re-established? (10 marks) Consider the following reaction: N 2 (g) + 3H 2 (g) 2 NH 3 (g) What concentration of NH 3 is in equilibrium with 1 x 10-3 M N 2 and 2.0 x 10-3 M H 2 at 700K? At this temperature Kc for the above process is

6 Q7. (a) Describe the galvanic cell that uses the following reaction. Cd (s) + Sn 2+ (aq) Cd 2+ (aq) + Sn(s) Write the anode and cathode half reactions and sketch the experimental setup. Label the anode and cathode, identify the sign of each electrode and indicate the direction of electron and ion flow. Write the cell diagram/shorthand notation for each of the following cells. (i) 3 Cu 2+ (aq) + 2Cr (s) 3 Cu (s) + 2Cr 3+ (aq) (ii) Pb (s) + 2H + (aq) Pb 2+ + H 2 (g) (5 marks) What is the cell potential at 25 o C for the following galvanic cell? Pb (s) /Pb 2+ (1.0M)// Cu 2+ (1x10-4 M)/Cu/(s/ If the Pb 2+ concentration is maintained at 1.0M, what is the Cu 2+ concentration when the cell potential drops to zero? (9 marks) 6

7 7