Binodal curves of 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF(4)) + sodium carbonate and 1-propyl-3-methylimidazolium tetrafluoroborate ([Pmim]BF(4)) + sodium carbonate systems have been determined experimentally at T = (288.15, 298.15, and 308.15) K, respectively. An empirical nonlinear expression which has four fitting parameters was used to reproduce experimental binodal data. The tie-line data were successfully correlated by the Othmer-Tobias and Bancroft and two-parameter equations. Good agreement was obtained with the experimental tie-line data with both models. Factors affecting the binodal curves such as temperature and nature of ionic liquids were also studied. It was demonstrated that two-phase area was expanded with a decrease in temperature, while the absolute value of slope of the ties slightly decreases with an increase in temperature. However, the binodal curves became more close to the origin with an increase in alkyl chain length of the ionic liquids (ILs) on the investigated systems. (C) 2011 Elsevier B.V. All rights reserved.