Answer Happy

Problem 2 - Prof Frazer and Lead Analysis (20 points) Professor Ronnie Frazer-Williams works at the Department of Chemistry of Fourah Bay College in Freetown, Sierra Leone. One of his research projects is to study lichens as bio-indicators of the extent of air pollution in and around major cities in Sierra Leone. Lichens are known to naturally absorb and accumulate heavy metals like lead. Heating a lichen sample with nitric acid converts lead compounds to lead nitrate, which may be analyzed by atomic absorption. Lead nitrate is an ionic solid in pure state, which solubility in water is characterized by the equilibrium: Pb(NO3)2(s) – Pb2+(aq) + 2NO, (aq), Ksp = 0.124 at 25°C Selected thermodynamic quantities for solid and aqueous lead nitrate at 25°C are given below. Substance ΔΗ, kJ/mol AGⓇkJ/mol 5.J/mol-K Pb(NO3)2(aq) -421.3 -246.9 303.3 Pb(NO3)(s) -451.9 to be determined to be determined

a) (3 pts) Based on K, calculate the value of Gºds for the dissolution of Pb(NO3)(s) in water. Report the result with three significant figures and proper units. b) (6 pts) From the values of AG as and known thermodynamic quantities in the table above, calculate the missing values of AG and for Pb(NO12{s). Show work. c) (3 pts) Suppose the lichen accumulates lead in the form of solid lead(II) carbonate. Treatment of solid lead(11) carbonate with aqueous nitric acid results in spontaneous dissolution and formation of a clear aqueous solution and bubbles of gas. Write a chemical equation in molecular form that explains this process d) (4 pts) Based on the description of reaction (c) and its chemical equation, do you expect the AGeen and Asan to be positive or negative? Explain briefly. e) (4 pts) Analysis of Pb(NO3)2(aq) by atomic absorption involves the use of a special AAS instrument in which the solution is heated to a very high temperature in reductive atmosphere, fully vaporized, and the resulting vapor is irradiated by light. Atoms of lead absorb light of certain wavelengths, which are detected and quantified in the instrument. To ensure the correct analysis, the lead should be fully vaporized. Assuming that lead becomes elemental in the AAS furnace and using the thermodynamic values below, calculate the temperature required to create the vapor pressure of lead equal to 1.00 x 10 atm. Use Lecture 22 for examples of such calculations. Substance AH, kl/mol SJ/mol K Pb(g) Pb(1) 17 195 88.0 175.3