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@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 0.2212. 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 7.445 wt % aqueous solution of LiBr.

@X@user.full_name@X@ @GMU: Which reactant in the reaction below is an acid (this one first in the answer) and which product is an acid?ClO-4 + H2SO4 → HClO4 + HSO-4

@X@user.full_name@X@ @GMU: How much time in seconds would it take for a 2.6316 g sample of 235U to decay to a mass of 1.7336 g if it has a half-life of 7.800e8 s.

@X@user.full_name@X@ @GMU: Calculate the [H3O+] of 114.01 mL of a buffer initially consisting of 0.1752 M C2H5NH2 and 0.1926 M C2H5NH3Br after addition of 0.0031 mol of HCl. Assume that no volume change occurs after addition of the acid. The Kb of C2H5NH2 is 5.60e-4

@X@user.full_name@X@ @GMU: How much time in hours would it take for a 2.7181 g sample of 137Cs to decay to a mass of 1.1715 g if it has a half-life of 9.461e8 s.

@X@user.full_name@X@ @GMU: What is the coefficient, b, in the reaction below, if Kc = 9.40e-6 and Kp = 0.0262 at 369.84°C?3A(s) + bB(g) → 4C(g)

@X@user.full_name@X@ @GMU: How much time in days would it take for a 2.6456 g sample of 3H to decay to a mass of 1.8024 g if it has a half-life of 3.879e8 s.

@X@user.full_name@X@ @GMU: When 10.52 g of aspirin was dissolved in 104.9 g of benzene, the freezing point was 275.7 K. What is the formula mass of this compound? The freezing point depression constant for benzene is 5.12 (°C*kg)/mol. The melting point and boiling points are 5.50°C and 80.10°C, respectively.

@X@user.full_name@X@ @GMU: Determine the molality of a 6.086 wt % aqueous solution of LiI.