We are asked to calculate the ratio of HPO42- to H2PO4 of the given buffer system and the concentrations of HPO42- and H2PO4-.
For Buffer 2: H2PO4- ↔ HPO42- + H+, pKa = 7.2
▪ Weak acid: H2PO4- (donates a proton, H+)
▪ Conjugate base: HPO42- (base formed after the weak acid donates or loses a proton, H+)
Using the Henderson-Hasselbalch equation for this buffer, we can determine the conj. base/ weak acid ratio at pH = 7.5.
The dissociation of H2PO4- to HPO42- has a pKa of 7.2. For a 0.2 M phosphate buffer at pH 7.5, calculate the following values.
a. the ratio of HPO42- to H2PO4
b. the concentrations of HPO42- and H2PO4-
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