code: def rhol_STP(self):
          r'''Liquid-phase mass density of the mixture at 298.15 K and 101.325 kPa,
          and the current composition in units of [kg/m^3].
  
          Examples
          --------
          >>> Mixture(['cyclobutane'], ws=[1]).rhol_STP
          688.9851989526821
          '''
          Vml = self.Vml_STP
          if Vml:
              return Vm_to_rho(Vml, self.MW)
          return Nonf rhol_STP(self):
          r'''Liquid-phase mass density of the mixture at 298.15 K and 101.325 kPa,
          and the current composition in units of [kg/m^3].
  
          Examples
          --------
          >>> Mixture(['cyclobutane'], ws=[1]).rhol_STP
          688.9851989526821
          '''
          Vml = self.Vml_STP
          if Vml:
              return Vm_to_rho(Vml, self.MW)
          return None
docs: r'''Liquid-phase mass density of the mixture at 298.15 K and 101.325 kPa,
          and the current composition in units of [kg/m^3].
  
          Examples
          --------
          >>> Mixture(['cyclobutane'], ws=[1]).rhol_STP
          688.9851989526821