Give the number of atoms of the specified element in a formula unit of each of the following compounds, and calculate the molecular (formula) mass:
a. Oxygen in aluminum sulfate, \(Al_{2}(SO_{4})_{3}\)
b. Hydrogen in ammonium hydrogen phosphate \((NH_{4})_{2}HPO_{4}\)
c. Oxygen in the mineral azurite, \(Cu_{3}(OH)_{2}(CO_{3})_{2}\)