code: def convert_compound(mass, source, target, element):
      
  
      # Perform the conversion.
      target_mass_fraction = element_mass_fraction(target, element)
      if target_mass_fraction == 0.0:
          # If target_formula does not contain element, just return 0.0.
          return 0.0
      else:
          source_mass_fraction = element_mass_fraction(source, element)
          return mass * source_mass_fraction / target_mass_fraction
docs: Convert the specified mass of the source compound to the target using
      element as basis.
  
      :param mass: Mass of from_compound. [kg]
      :param source: Formula and phase of the original compound, e.g.
        'Fe2O3[S1]'.
      :param target: Formula and phase of the target compound, e.g. 'Fe[S1]'.
      :param element: Element to use as basis for the conversion, e.g. 'Fe' or
        'O'.
  
      :returns: Mass of target. [kg]