Surface tension and 0.1 MPa density data for 1-CnCn-3-methylimidazolium iodides with n=3n=3, 4, and 6, validated using a parachor and group contribution model

• Properties of 1-Cn-3-methylimidazolium iodides, with n = 3, 4, 6 were investigated.
• We report density and surface tension data for still poorly studied ionic liquids.
• We analyze the density data within the group contribution concept.
• Exner’s parachor additivity test is presented for 33 ionic liquids from 8 series.
• The parachor contribution per alkyl inner CH2 group is 32.8 parachor units.

Experimental data over the temperature range from (283 to 365) K are presented on the 0.1 MPa density and (air + liquid) interfacial tension for three 1-CnCn-3-methylimidazolium iodides with n=3n=3, 4, and 6 still poorly or even not studied in these respects at all. The reported density data were obtained using a single-sinker buoyancy method with an estimated combined expanded uncertainty at 0.95 confidence level Uc=1.0Uc=1.0 kg · m−3 (7·10-4ϱ7·10-4ϱ). The surface tension data were obtained by the Wilhelmy plate method with Uc=0.08Uc=0.08 mN · m−1 and by du Noüy ring method with Uc=0.3Uc=0.3 mN · m−1. The Krűss K100MK2 tensiometer was used to determine the buoyancy and surface tension forces. The density data obtained for the three studied ionic liquids match a single common group contribution model within their experimental uncertainties, which indirectly supports the data validity. Similar single common model for the surface tension data, based on the parachor, results in two times greater average absolute relative deviation of the data than provide empirical models developed for each ionic liquid separately. For the CH2 parachor group contribution a value of 32.8 (mN · m−1)1/4 mol · cm−3 was obtained, based on surface tension and density data for 33 ionic liquids at T = 298.15 K.