在278.15—318.15K范围内DMF-H_2O体系的超额摩尔体积及DMF的表观摩尔体积和偏摩尔体积的测定与研究

EXCESS MOLAR VOLUMES OF MIXTURES OF N, N-DIMETHYLFORMAMIDE AND WATER AND APPARENT MOLAL VOLUMES AND PARTIAL MOLAL VOLUMES OF N, N-DIMETHYLFORMAMIDE IN WATER FROM 278. 15K TO 318. 15K

本文应用振动管式密度计,测定了278.15—318.15K范围内10个温度下,DMF-H_2溶液的密度随组成的变化.根据密度值求出溶液的超额体积VE;在全部浓度的范围内不同组成下DMF的表观摩尔体积φv及偏摩尔体积V_(DMF);及VE、φv和V_(DMF)随组成变化的规律.发现V_(DMF)随x_(DMF)的变化与NaCl由水至DMF-H_2O溶液的转移熵有对应的变化规律,均在x_(DMF)≈0.075处有极值,从而进一步对DMF-H_2O的液体结构进行了讨论,认为当x_(DMF)=0.075时,单个DMF分子可能嵌入12个水分子组成的分子笼中,从而形成最紧密结构。

The densities of the mixtures of N,N-Dimethylformamide (DMF) and water(w)have been measured at ten temperatures from 278. 15K to 318. 15K with the vibra-tingtube density meter(Anton Paar Model DMA602). Then the excess molal volumes V^Eof solutions and apparent and partial molal volumes of DMF over the range of molefraction 0-1 have been determined. Comparing these quantities as functions of molefraction of mixtures with the standard entropies of transfer for NaCl from water toDMF-H_2O mixtures as function of mole fraction of mixed solvent we found out thereis a correspondence between the V_(DMF) varied with x and the standard entropies oftransfer of NaCl. Both have the extremes at x=0. 075. Therefore the structure of so-lution have been discussed. It might be considered that monomeric DMF moleculeshave been trapped in a quasi-clathrate 'cage' made up of 12 water molecules at x=0.075 forming the possible closest packing of particles.