单分子膜法测阿伏伽德罗常数实验中扩散剂的新探索

在单分子膜法测阿伏伽德罗常数实验中,为了克服扩散剂苯毒性大且实验误差大等缺点,通过查阅文献资料,发现环己烷、正己烷的物理性质符合在实验中作扩散剂的要求,并且毒性较苯低,所以选用环己烷、正己烷与苯做对比实验。实验结果表明,用环己烷作扩散剂测得的NA最接近理论值。故在用单分子膜法测阿伏伽德罗常数的实验中,环己烷可以代替苯作扩散剂。既能减小实验误差,又可以降低实验过程中有毒药品对实验者的危害。     

Thermoynamic properties (Hm, CP,m, Vm, κT) of binary mixtures {x1,3-Dioxane + (1−x)Cyclohexane} at 298.15 K

Molar excess enthalpies H_m^E, isobaric heat capacities C_P,m^E, volumes V_m^E and isothermal compressibilities κT^E for the 1,3-dioxane(3DX) + cyclohexane mixture were measured at 298.15 K, in order to compare to those of the 1,4-dioxane(4DX) + cyclohexane mixture. H_m^E is endothermic and the maximum value about 1.5 kJ mol⁻¹ at x ≈ 0.45, and lower than that of the 4DX mixture by about 80 J mol⁻¹. V_m^E is positive over the whole concentration and the maximum value is about 0.85 cm³ mol⁻¹ at x ≈ 0.45, and lower than that of the 4DX mixture. The above results suggest the energetic unstabilization, resulting in the volume expansion in the mixture. C_P,m^E shows the characteristic W-shaped concentration dependence, which has maximum at x ≈ 0.45 and two minima at x ≈ 0.1 and 0.9. The maximum C_P,m^E value for 3DX mixture shifts toward the positive side, compared to that of 4DX mixture. κT^E were estimated from speeds of sound, densities, thermal expansion coefficients and isobaric heat capacities of the pure component liquids and the mixtures. The κT^E result shows the positive concentration dependence over the whole composition range. The 3DX mixture has the similar thermodynamic properties to the 4DX mixture, despite that 4DX is the nonpolar solvent and 3DX is the dipolar liquid. this means that there exists the local dipolar interaction between 4DX molecules, and the prevalence of “microheterogeneity” in the both mixtures.