def __update_molar_mass(self, compound='', element=''):
        """Re-calculate the molar mass of the element given due to stoichiometric changes

        Parameters:
        ==========
        compound: string (default is '') name of compound
        element: string (default is '') name of element
        """
        _molar_mass_element = 0
        list_ratio = self.stack[compound][element]['isotopes']['isotopic_ratio']
        list_mass = self.stack[compound][element]['isotopes']['mass']['value']
        ratio_mass = zip(list_ratio, list_mass)
        for _ratio, _mass in ratio_mass:
            _molar_mass_element += np.float(_ratio) * np.float(_mass)
        self.stack[compound][element]['molar_mass']['value'] = _molar_mass_element
Re-calculate the molar mass of the element given due to stoichiometric changes

        Parameters:
        ==========
        compound: string (default is '') name of compound
        element: string (default is '') name of element