Uranium is distributed in a form called yellow cake, which is made from uranium ore. In the second step of the reactions that form yellow cake from uranium ore, uranyl sulfate, UO2SO4, is converted to (NH4)2U2O7. 2UO2SO4 + 6NH3 + 3H2O → (NH4)2U2O7 + 2(NH4)2SO4

a. What is the maximum mass, in kilograms, of (NH4)2U2O7 that can be formed from the reaction of 100 kg of water and 100 kg of ammonia with 481 kg of UO2SO4?

  b. Explain why two of these substances are in excess and one is limiting.