@X@user.full_name@X@ @GMU: Uranium -238 decays in a series of steps to Pb-206. When the material is very old, one can treat the kinetics as a decay directly to Pb and the ratio of these two can be treated as a measure of the age of a rock. A rock containing 238U and 206Pb was examined to determine its approximate age. The molar ratio of 206Pb to 238U was 0.1807. Assuming no lead was originally present and that all lead formed remained in the rock, what is the age of the rock (in years)? The half-life of 238U is 4.50e9 yr.

@X@user.full_name@X@ @GMU: Determine the molality of a 8.268 wt % aqueous solution of LiCl.

@X@user.full_name@X@ @GMU: What is the pH of 6.69e-3 M H2SO4 ?

@X@user.full_name@X@ @GMU: The osmotic pressure of an unknown solution is 403.809 mm Hg at 17.78 °C. Which of the solutions below is the most likely one? Assume any salt is completely ionic!

@X@user.full_name@X@ @GMU: The osmotic pressure of a 11.027 mM solution of K2SO4 is 0.530 atm at 18.22 °C. How many ions per formula unit of K2SO4 must there be? The compound may not be completely ionic.

@X@user.full_name@X@ @GMU: What is the equilibrium concentration of H3O+ in 0.1216 M HF? See reaction belowHF + H2O → F- + H3O+ Ka = 6.600×10-4

@X@user.full_name@X@ @GMU: What is the standard free energy change for the ionization of HF acid, if its Ka is 6.60e-4.

@X@user.full_name@X@ @GMU: What is the pOH of 9.35e-4 M HNO3 ?

@X@user.full_name@X@ @GMU: Initially there were equilibrium concentrations of 0.3709 M A, 0.2658 M B, and 0.1997 M C. Which change will cause the equilibrium to shift from left to right if the reaction is exothermic? Use the reaction below.4A(aq) → 3B(aq) +4C(aq) K = 0.600

John Schreifels @GMU: What is the total entropy change at 25oC for the reaction below, if the standard entropies of reactants and products are So (C(gr)) = 5.74 J/mol*K, So (H2(g)) = 130.68 J/mol*K, and So (C9H16(g)) = 484.8200 J/mol*K and the heat of formation of C9H16(g)) is 61.8300 kJ/mol.9C(gr) + 8H2(g) → C9H16(g)