Effect on pH of sodium bisulphite addition

[tipp79]

I am wanting to confirm the impact on pH of sodium bisulphite being added to water. To do so, I need to calculate the number of H ions liberated when sodium bisulphite (NaHSO3) is added to water. For example, I know for ferric chloride the reaction is

FeCl3+3H20 ⇌ Fe(OH)3+ 3H+ + 3Cl-

i.e. 3 Hs and acidity is released. What is the equivalent reaction for NaHSO3 and H20? Thanks

 

[bimr]

It is a very complex reaction with various ionic species in equilibrium.

The amount of CO₂ present in the finished solution depends on by the type of system and the pressure. If the system is open to the atmosphere, the reaction is driven to the right and the dissolved CO₂ is released to the atmosphere. The pH will tend to increase with the release of the CO₂.

If the finished solution is pressurized, the final solution will hold the CO₂ in solution. The retained carbonic acid will tend to slightly lower the pH and be mildly acidic.

When the CO₂ is released from solution, the reaction is driven to the right side of the equation, the concentration of acid ions decreases, but the hydroxides from the equilibrium B are still present. The ultimate end products from the reaction in an open system (open to the atmosphere) with a low partial pressure of CO₂ will have a slightly higher pH, and can be described as mildly alkaline solution.