Answer:
pH of the buffer is 7.48
Explanation:
The H₂PO₄⁻/HPO₄²⁻ buffer has a pKa of 7.21. You can find pH of this buffer following H-H equation:
pH = pKa + log [A⁻] / [HA]
pH = 7.21 + log [HPO₄²⁻] / [ H₂PO₄⁻]
<em>Where [] represents molarity of each specie of the buffer and, as volume is 1.00L, also represents its moles.</em>
Thus, to find pH of the buffer we need to calculate moles of each specie, thus
Moles of 18.0g of KH₂PO₄(Molar mass: 136.086g/mol) = moles of H₂PO₄⁻ are:
18.0g KH₂PO₄ ₓ (1mol / 136.086g) = 0.132 moles of KH₂PO₄= H₂PO₄⁻
Moles of 35.0g of Na₂HPO₄(Molar mass: 141.96g/mol) = moles of HPO₄²⁻ are:
35.0g Na₂HPO₄ ₓ (1mol / 141.96g) = 0.2465 moles of Na₂HPO₄= HPO₄²⁻
Replacing in H-H equation:
pH = 7.21 + log [HPO₄²⁻] / [ H₂PO₄⁻]
pH = 7.21 + log [0.2465] / [0.132]
pH = 7.48
<h3>pH of the buffer is 7.48</h3>
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