def get_total_mass(self):
        """Returns the total mass in g/mol.

        Args:
            None

        Returns:
            float:
        """
        try:
            mass = self.loc[:, 'mass'].sum()
        except KeyError:
            mass_molecule = self.add_data('mass')
            mass = mass_molecule.loc[:, 'mass'].sum()
        return mass