The phosphate buffer system is very important for maintaining the ph of the cytoplasm of all cells. phosphoric acid is a triprotic acid; however, the relevant equilibrium in the biologically useful, neutral range, with a pka of 6.86, is that of dihydrogen phosphate and monohydrogen phosphate ions: h3po4 ⇌ h2po4- + h+ pka = 2.14 h2po4- ⇌ hpo42- + h+ pka = 6.86 hpo42- ⇌ po43- + h+ pka = 12.4 using the henderson-hasselbalch equation, calculate the ph of a solution containing 0.042 m nah2po4 and 0.058 m na2hpo4.

The pH is 7.0

Explanation:

The equilibrium relevant for the problem is:

H₂PO4⁻ ⇌ HPO4⁻² + H⁺        pKa = 6.86

The Henderson-Hasselbalch (H-H) equation describes the pH of a buffer solution, using the concentrations of the acid and its conjugate base:

For this case, [A⁻] = [HPO4⁻²], and [HA] = [H₂PO4⁻]. Thus:

We put the concentrations and pka given in the problem in the H-H equation:

P.S.: The actual pka for the equilibrium is 7.21, according to literature. Not 6.86 like the problem says. If we use a pka of 7.21 then the pH would be 7.35.

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