def standard(target, mol_weight='pore.molecular_weight', density='pore.density'
    ):
    """
    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.

    mol_weight : string
        The dictionary key containing the molecular weight in kg/mol

    density : string
        The dictionary key containing the density in kg/m3

    Returns
    -------
    value : NumPy ndarray
        Array containing molar density values [mol/m3]

    """
    MW = target[mol_weight]
    rho = target[density]
    value = rho / MW
    return value
