The reactive solid-liquid equilibrium (SLE) in the quinary system 2-keto-L-gulonic acid (HKGA) + sodium-2-keto-L-gulonate (NaKGA) + hydrochloric acid (HCl) + sodium chloride (NaCl) + water was studied experimentally at 298 K and ambient pressure. The precipitation of three solid species was observed: HKGA monohydrate (HKGA center dot H2O), NaKGA monohydrate (NaKGA center dot H2O), and NaCl. A thermodynamic model based on the Pitzer model to calculate the activity coefficients in the liquid phase for the SLE was developed and unreported Pitzer parameters were fitted to the experimental data of this work. The equilibrium constant for the dissociation of HKGA and the solubility products of HKGA center dot H2O and NaKGA center dot H2O at 298 K were calculated from experimental data, whereas the equilibrium constant for the autoprotolysis of water and the solubility product of NaCl were adopted from literature data. The agreement between the experimental data and the results from the model is excellent, both regarding the liquid phase composition and the solid species in solid-liquid equilibrium. (C) 2019 Elsevier B.V. All rights reserved.