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WAChemistryQuick questions

Unit 3: Equilibrium, Acids and Bases, and Redox

Quick questions on Polyprotic acids: WACE Year 12 Chemistry

2short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What is sulfuric acid is a special case?
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Sulfuric acid is strong in its first ionisation (H2SO4β†’H++HSO4βˆ’\text{H}_2\text{SO}_4 \rightarrow \text{H}^+ + \text{HSO}_4^-, essentially complete) but weak in its second (HSO4βˆ’β‡ŒH++SO42βˆ’\text{HSO}_4^- \rightleftharpoons \text{H}^+ + \text{SO}_4^{2-}, an equilibrium). This mixed behaviour is worth remembering because it differs from a fully weak acid like phosphoric acid.
What are effect on titrations?
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Because the protons come off in distinct steps, a titration of a polyprotic acid against a strong base can show more than one equivalence point, one for each proton being neutralised. A diprotic acid can show two end points and a triprotic acid up to three, provided the successive constants are far enough apart to resolve them.

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