The pH of tap and deionized water at 13, 23, 33, and 43 oC in the range of 0-140 g/L of NaCl salinity

Abstract The pH of water used to prepare liquid solutions and brines for various types of biochemical investigations may influence the experimental results and overall conclusions. The pH of four types of water such as tap, tap boiled, deionized and deionized boiled water were investigated at the temperatures of 13, 23, 33 and 43 oC in the salinity range of 0-140 g/L of NaCl. The pH of tap water decreased by 2 on average after deionization. The pH of tap water and brines varied from 7 to 9.5 while it varied from 5.1 to 6.5 for deionized water and brines at all salinities. The pH of tap water increased by 0.5-1.5 due to CO2 release while the pH of deionized water did not change after boiling in 30 minutes. The addition of salt of more than 20 g/L of NaCl caused the pH decrease by 1-1.5. The pH of tap boiled and deionized boiled brines decreased with the temperature increase by 0.1 per 10 oC. The decreasing, increasing and neutral trends of pH change with the increase in salinity were observed. The brines of tap water, tap boiled water and deionized water were close to constant at 20-120 g/L. The increase in pH from 80 g/L for deionized boiled water could be addressed to a salting out effect because of the lower CO2 solubility at highly concentrated brines.