I am preparing buffered hypochlorite reagent for an experiment. The paper says to "Dissolve 1.48g of NaOH in 70mL water, add 4.98g Na
2HPO
4 and 20mL of sodium hypochlorite (5% NaOCl). Use less or more hypochlorite solution if the NaOCl concentration is higher or lower than indicated. Check pH to ensure value between 11.4-12. Add additional NaOH if required to raise pH. Dilute to 100mL."
I need to calculate the pH of the solution. I can measure it after with a pH meter but I have to be able to show the calculation. I am using H-H to calculate buffer pH.
The relevant equations are
HPO
42- + H
2O
PO
43- + H
3O
+ Ka = 2.2x10
-13 HClO + H
2O
ClO
- + H
3O
+ Ka = 3.0x10
-8The first reaction is NaOH and dibasic sodium phosphate
Na
2HPO
4 + NaOH
Na
3PO
4 + H
2O
How do I proceed with H-H to get pH of the solution? What are the species partaking in buffering the hypochlorite?