Answer:
7.58
Explanation:
Given that
A buffer solution obtained by dissolving 13.0 g of KH₂PO₄ and 26.0 g of Na₂HPO₄ in water and then diluting to 1.00 L.
pKa = 7.21.
To get the PH we are going to use Henderson - Hasselblach equation:
PH = Pka + ㏒ [A/AH]
when the molar mass of Na2HPO4 = 142 g/mol
and A is the conjugate base HPO4-- ions so,
∴[A] = 32g / 142 g/mol
= 0.225 M
and when the molar mass of KH2PO4 = 136 g/mol
and AH is the weak acid H2PO4- ions so,
∴[AH] = 13 g / 136 g/mol
= 0.096 M
and when we have the Pka value of H3PO4 = 7.21
so, by substitution:
∴ PH = 7.21 + ㏒ (0.225 / 0.096)
= 7.58
