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Explain the role of the conjugate acid/base pair, H₂PO₄⁻/HPO₄²⁻, in maintaining the pH of living cells - HSC - SSCE Chemistry - Question 25 - 2011 - Paper 1

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Explain the role of the conjugate acid/base pair, H₂PO₄⁻/HPO₄²⁻, in maintaining the pH of living cells. Include chemical equations in your answer.

Worked Solution & Example Answer:Explain the role of the conjugate acid/base pair, H₂PO₄⁻/HPO₄²⁻, in maintaining the pH of living cells - HSC - SSCE Chemistry - Question 25 - 2011 - Paper 1

Step 1

State the role of H₂PO₄⁻/HPO₄²⁻ as a buffer system in the cell.

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Answer

The conjugate acid/base pair H₂PO₄⁻ and HPO₄²⁻ serves as an important buffer system in living cells. Buffers are substances that help maintain a stable pH in biological systems despite the addition of acids or bases. In the case of the H₂PO₄⁻/HPO₄²⁻ buffer system, it can neutralize excess hydrogen ions (H⁺) or hydroxide ions (OH⁻) that may otherwise disrupt cellular processes.

Step 2

Provide two correct equations.

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Answer

  1. When there is an excess of hydrogen ions, the reaction shifts to the left:

    H2PO4−+H+⇌H3PO4H₂PO₄⁻ + H⁺ \rightleftharpoons H₃PO₄

    This reaction decreases the concentration of free H⁺ ions, thereby reducing acidity and stabilizing pH.

  2. Conversely, when excess hydroxide ions are present, the reaction shifts to the right:

    HPO42−+H+⇌H2PO4−HPO₄²⁻ + H⁺ \rightleftharpoons H₂PO₄⁻

    This neutralizes the hydroxide ions, helping to maintain the pH balance.

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