Hello, I am working in the characterization of some activated carbons. In the determination of the point of zero charge by pH measurement. Some methods mentions the use of an electrolyte (0.1 M NaCl) prior to the adjustment of pH with HCl or NaOH, could you tell me what is the role of the NaCl in this process? Thank you so much
The value of pH is used to describe pzc only for systems in which H+/OH− are the potential-determining ions (which is the common case). Generally, pzc is the value of the negative decimal logarithm of the activity of the potential-determining ion in the bulk fluid. For example, the charge on the surface of silver iodide crystals may be determined by the concentration of iodide ions in the solution above the crystals. Then, the pzc value of the AgI surface will be described by the concentration of I− in the solution (or negative decimal logarithm of this concentration, pI−).
In case of NaCl(brine solution) ie Na+/Cl-
HCl + NaOH → NaCl + H2O
The task of any pH adjustment system is to adjust the pH of the process stream into the defined acceptable discharge range. In the case of an acid neutralization, caustic (NaOH) is added to the effluent stream to pH Neutralize the solution. This neutralization, or titration can be expressed as follows:
HCl + NaOH → NaCl + H2O
In the example shown above hydrochloric acid (HCl) is neutralized with caustic (NaOH) and yields ordinary table salt (NaCl) and neutral water. NaCl, being very soluble in water, remains dissolved in solution, and very little or no solids are generated. It is the task of the pH adjustment system to add just the right amount of caustic to achieve the end point of the neutralization that is desired. This is not quite as simple as it may seem because of the logarithmic nature of the pH titration curve (remember the definition of pH above)..
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