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4.10 Relative Strengths of Acids and Bases

4.10 Relative Strengths of Acids and Bases. Chemistry 12. 4.10. In this lesson we will look at the relative strengths of some weak acids and use their Ka values to explain how they would behave when they are combined. 4.10. HPO 4 2- + HCO 3 -. amphiprotic. Can only act as a base.

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4.10 Relative Strengths of Acids and Bases

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  1. 4.10 Relative Strengths of Acids and Bases Chemistry 12

  2. 4.10 In this lesson we will look at the relative strengths of some weak acids and use their Ka values to explain how they would behave when they are combined.

  3. 4.10 HPO42- + HCO3- amphiprotic Can only act as a base E.g. 1a) Write the Bronsted-Lowry acid base equilibria for the following reactants. H2PO4- + CO32- ↔

  4. 4.10 Ka = 6.2 x10-8 Ka = 5.6 x10-11 E.g. 1b) What side is favoured? H2PO4- + CO32- ↔ HPO42- + HCO3- Larger Ka value means that H2PO4- is better at producing H+ products are favored

  5. 4.10 E.g. 1c) What is the stronger base? H2PO4- + CO32- ↔ HPO42- + HCO3- A stronger acid is ALWAYS on the same side as the stronger base CO32- is the stronger base

  6. 4.10 SO42- + H3PO4 E.g. 2 a) Using 2 amphiprotic reactants HSO4- + H2PO4-↔ HINT: Use your B-L table, as the reactant with the larger Ka will behave like an acid.

  7. 4.10 Ka = 1.2 x10-2 Ka = 7.5 x10-3 E.g. 2b) What side is favored? HSO4- + H2PO4-↔ SO42- + H3PO4 the products are favoured

  8. 4.10 Stronger acid  Stronger base E.g. 2c) Stronger base? HSO4- + H2PO4-↔ SO42- + H3PO4

  9. 4.10 Both reactants dissociate and Na+ is a spectator These are our reactants You should notice that this is really the same question as example 2. E.g. 3) What is the Bronsted-Lowry acid base equilibria that results from the following reactants? NaHSO4 + NaH2PO4 NaHSO4  Na+ + HSO4- NaH2PO4 Na+ + H2PO4- HSO4- + H2PO4-↔ SO42- + H3PO4

  10. Learning Check When given 2 weak acids can you determine which one will act as the acid and which one will act as the base? Can you identify whether the equilibrium favours the reactants or the products? Can you do the above with amphiprotic substances? Salts?

  11. 4.10 Read & Highlight Self Notes (p. 6 – 12) Problems Hebden # 38-46

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