@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 0.1852. 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: Which base listed below would be the best to creat a buffer having a pH of 7.7461?

@X@user.full_name@X@ @GMU: What is the pH of 4.42e-4 M HNO3 ?

@X@user.full_name@X@ @GMU: What is the temperature at which the reaction below becomes spontaneous, if the standard entropies of reactants and products at 25oC are So (C(gr)) = 5.74 J/mol*K, So(H2(g)) = 130.68 J/mol*K, and So (C6H6(g)) = 269.2000J/mol*K and the heat of formation of C6H6(g)) is 82.9300 kJ/mol?C6H6(g) → 6C(gr) + 3H2(g)

@X@user.full_name@X@ @GMU: What is the pH of a 0.1888 M HNO2 ? See reaction belowHNO2 + H2O → NO-2 + H3O+ Ka = 4.600×10-4

@X@user.full_name@X@ @GMU: Which base listed below would be the best to creat a buffer having a pH of 6.1764?

@X@user.full_name@X@ @GMU: Initially there were equilibrium concentrations of 0.3387 M A, 0.2024 M B, and 0.1151 M C. Which change will cause the equilibrium to shift from left to right if the reaction is endothermic? Use the reaction below.5A(aq) → 3 B(aq) +2 C(aq) K = 0.999

@X@user.full_name@X@ @GMU: The osmotic pressure of an unknown solution is 510.741 mm Hg at 25.27 °C. Which of the solutions below is the most likely one? Assume any salt is completely ionic!

@X@user.full_name@X@ @GMU: What is the conjugate base and base dissociation constant of H2O2 if its acid dissociation constant is 2.400×10-12 ?

@X@user.full_name@X@ @GMU: What is the solubility in g/L of CH3Br at a partial pressure of 457.9 torr, if the solubility at a partial pressure of 363.1 torr is 7.211 g/L?