This paper presents an established relationship between the pH of ammonia solution and its carbonation ratio (a). The aim of this correlation is to track the amount of CO2 absorbed or the amount of CO2 released from ammonia solvent. Furthermore, this paper studies the evolution of density and viscosity of ammonia solution with the carbonation ratio because those physical properties can significantly affect liquid side mass transfer coefficient. Experiments have been carried out in a thermoregulated Lewis-type cell reactor and the measures have been done using three concentrations of ammonia (3, 5 and 7 wt %) and temperatures (293, 303 and 313 K). Results show that the estimated function has a high correlation coefficient which indicates a relationship between variables. All results show a linear correlation between viscosity and carbonation ratio, and between density and carbonation ratio.