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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⁻/HPO₄²⁻ plays a crucial role in maintaining the pH of living cells by acting as a buffer system. Buffers resist changes in pH when small amounts of acids or bases are added. In the cellular environment, this pair can donate protons (H⁺) when the pH increases (becoming less acidic) and can accept protons when the pH decreases (becoming more acidic), thus stabilizing the pH.

Step 2

Provide two correct equations

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Answer

  1. When the pH of the solution decreases (adding acid):

    HPO42−+H+⇌H2PO4−HPO₄^{2-} + H^{+} \rightleftharpoons H₂PO₄^{-}

    This reaction shows HPO₄²⁻ acting as a base, accepting a proton to form H₂PO₄⁻.

  2. When the pH of the solution increases (adding base):

    H2PO4−⇌HPO42−+H+H₂PO₄^{-} \rightleftharpoons HPO₄^{2-} + H^{+}

    In this reaction, H₂PO₄⁻ acts as an acid, donating a proton to form HPO₄²⁻.

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