code: def standard(target, mol_weight='pore.molecular_weight',
               density='pore.density'):
      r
      MW = target[mol_weight]
      rho = target[density]
      value = rho/MW
      return value
docs: r"""
      Calculates the molar density from the molecular weight and mass density
  
      Parameters
      ----------
      target : OpenPNM Object
          The object for which these values are being calculated.  This
          controls the length of the calculated array, and also provides
          access to other necessary thermofluid properties.
  
      pore_MW : string
          The dictionary key containing the molecular weight in kg/mol
  
      pore_temperature : string
          The dictionary key containing the density in kg/m3