Abstract The chloride-water mixture and the chloride-water-acetone mixtures were studied by measuring the 35Cl NMR spectra. From the line-width analyses, it has been concluded that the line-widths of the chloride solutions are affected only by the nearest neighbours of the chloride ions, which makes it possible to study the interaction between the chloride ion and the solvent molecules microscopically. The problem concerning the ion pair formation in solutions was discussed. It has been shown that the observation of the concentration dependence of line-widths can be very powerful method for the detection of contact ion pairs formed in the solutions.