Mean activity coefficients of 1:1 electrolytes

Measured γ± of NaCl and HCl in water at 25 °C beside the values of the Debye–Hückel limiting law, the extended law (å = 4.7 Å) and the Davies equation, with the Debye length at each molality.


0.001	0.965	0.965	0.963	0.965	0.965	96.2
0.005	0.928	0.929	0.920	0.928	0.927	43.0
0.010	0.903	0.905	0.889	0.903	0.902	30.4
0.050	0.822	0.832	0.769	0.822	0.821	13.6
0.100	0.779	0.797	0.689	0.779	0.781	9.6
0.500	0.681	0.759	0.435	0.672	0.733	4.3
1.000	0.657	0.811	0.308	0.630	0.790	3.0
2.000	0.668	1.009	0.189	0.593	1.017	2.2
3.000	0.714	1.316	0.130	0.574	1.367	1.8
6.000	0.986	3.230	0.056	0.548	3.604	1.2

Model columns come from the site’s kernel: A = 0.5108, B = 0.3287 Å⁻¹, Bjerrum length 7.16 Å; å = 4.7 Å is the least-squares fit of the extended law to the NaCl data up to 0.1 mol kg⁻¹. These formulas see only charge and give NaCl and HCl the same value; the two salts part company above 0.1 mol kg⁻¹ because of short-range effects such as ion hydration.

Sources

W. J. Hamer & Y.-C. Wu, “Osmotic coefficients and mean activity coefficients of uni-univalent electrolytes in water at 25 °C”, J. Phys. Chem. Ref. Data 1, 1047–1099 (1972), Tables 4 (HCl) and 16 (NaCl).
C. G. Malmberg & A. A. Maryott, J. Res. Natl. Bur. Stand. 56, 1–8 (1956): relative permittivity of water, 78.30 at 25 °C, from which A, B and the Debye length are computed.

Used in these lessons

Activities and the salt effect