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@X@user.full_name@X@ @GMU: What would the [H3O+] be after addition of 13.43 mL of 0.1000 M NaOH to 25.00 mL of 0.1000 HA (a weak acid, Ka = 5.55e-5)?

@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 0.2165. 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: Calculate the [H3O+] of 105.66 mL of a buffer initially consisting of 0.1353 M N2H4 and 0.1741 M N2H5Cl after addition of 0.0022 mol of HCl. Assume that no volume change occurs after addition of the acid. The Kb of N2H4 is 8.90e-7

@X@user.full_name@X@ @GMU: How much time in seconds would it take for a 2.3265 g sample of 18F to decay to a mass of 1.7372 g if it has a half-life of 6.588e3 s.

John Schreifels @GMU: What is the change in mass of 197Au when it is formed from protons, electrons and neutrons if the atom has a mass of 203.97302 amu? The masses of the proton, electron and neutron are 1.00728 amu, 0.000549 amu and 1.00867 amu, respectively.

@X@user.full_name@X@ @GMU: The reaction below occurs in an electrochemical cell. Which substance would be the best solid electrode in the given half-cell?Pb2+(aq) + Sn(s) → Pb(s) + Sn2+(aq)

@X@user.full_name@X@ @GMU: The vapor pressure of C2H5OH (l) at 320.4 K is 209.7 mm Hg. What is the heat of vaporization if its normal boiling point is 351.6 K?

@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 potential of a cell at 25oC for which the reaction below applies, if the molar concentrations of Ni2+(aq) and H+ are 0.164 M and 2.88e-6 M, respectively? The H2(g) pressure is 1 atm at 25oC.2H+(aq) + Ni(s) → Ni2+(aq) + H2(g) Ecoell = 0.260 V

@X@user.full_name@X@ @GMU: What is the rate of consumption of A (M/s), if the rate of consumption of C is 0.326 M/s? Use the reaction below:2A + 3B + 6C → products