| Sodium silicate solution has a wide range of use in the chemical industry, foundry, construction and metallurgy industry, and also much geochemical process involves its physical and chemical properties, especially the thermodynamics. Therefore, the thermodynamics prope-rties of sodium silicate solution has an important role in the production practice. The research work is as follows:1. The structure of sodium silicate solution was investigated by infrared spectra and the structure variations with the modulus (molar ratio of SiO2 and Na2O), SiO2 concentration and storage time were got.2. The osmotic coefficients have been determined for the system NaOH-Na2H2SiO4-H2O at 313.15 K by the ispiestic method in the ionic streng-th from 0.5695 mol-kg-1 to 6.4775 mol-kg"1 and modulus from 0.1461 to 0.3158. The experimental data have been represented by the Pitzer model of osmotic coefficients. The Pitzer ion interaction parameters for NaOH-Na2H2SiO4-H2O system were evaluated from experimental data using multiple regression. Therefore, the pure electrolyte parameters of Na2H2SiO4 were as follows:βNa2H2SiO4(0)=-0.92907,βNa2H2SiO4(1).=7.21856, CNa2H2SiO4Φ.=0.53964, and the mixed electrolyte parameters were as follows:θNa+,H2SiO42-=1,ΨNa+,H2SiO42-,OH.=-0.20913. The mean activity coefficients of NaOH and Na2H2SiO4 were also calculated for the NaOH-Na2H2SiO4-H2O syst-em, and these calculations establish their variations with ionic strength and modulus.3. The isobaric heat capacities have been measured for the system NaOH-Na2H2SiO4-H2O in the temperature ranges of 298～362 K, ionic strength ones of 1.2393～6.0928 mol-kg-1, and modulus of 0.0790～0.4200. The experimental data of apparent molar isobaric heat capacities were modeled. Therefore, the apparent molar isobaric heat capacities were recalculated and these calculations establish their variations with ionic strength, modulus and temperature.
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