New liquid-liquid equilibriumdata for polyethylene glycol (PEG) 3000+ CHO2K+ H2O systems were measured at 298.15 K and pH values of 7.95, 8.40 and 9.98. It was found that an increase in pH caused the binodal curve to be displaced downward and the two-phase region to expand. Accordingly, the binodal curve was adjusted to the Pirdashti equation and the tie-line compositions were correlated using the Othmer-Tobias, Bancroft and Hand equations. The study measured the refractive index and densities of several homogeneous binary and ternary solutions. The solutions were used for calibration within a range of 0% to 30% of the mass of the PEG and potassium formate. The density and refractive index data show a linear variation with themass fraction of the polymer and the salt. The effect of pH on the binodal, tie-line lengths (TLL) and slope of the tie-line (STL) in the systems was examined. Itwas found that an increase in pHincreased the TLL and decreased the STL. Itwas observed that the density of the aqueous two-phase system was influenced by the TLL. The difference in density between phases (Delta rho) increased as the TLL and pH increased. It was found that the TLL and Delta rho showed a linear relationship. The effective excluded volume (EEV) of the PEG was obtained and it was found that EEV also increased as the pH increased. (C) 2017 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.