4.10 Relative Strengths of Acids and Bases

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 E.g. 1a) Write the Bronsted-Lowry acid base equilibria for the following reactants. HPO4 2- + HCO3H2PO4- + CO32- amphiproti c

Can only act as a base 4.10 E.g. 1b) What side is favoured? H2PO4- + CO32- HPO4 Ka = 6.2 x10-8

2- + HCO3- Ka = 5.6 x1011 Larger Ka value means that H2PO4- is better at producing H+ 4.10

E.g. 1c) What is the stronger base? H2PO4- + CO32- HPO4 2- + HCO3- A stronger acid is ALWAYS on the same side as the stronger base CO32- is the stronger base

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

HSO4- + H2PO4- SO42- + H3PO4 Ka = 1.2 x10-2 Ka = 7.5 x10-3 the products are favoured 4.10 E.g. 2c) Stronger base? HSO4- + H2PO4- SO42- + H3PO4 Stronger acid

Stronger base 4.10 E.g. 3) What is the Bronsted-Lowry acid base equilibria that results from the following reactants? Both reactants NaHSO4 + NaH2PO4 NaHSO4 Na+ + HSO4NaH2PO4 Na+ + H2PO4- dissociate and Na+

is a spectator These are our reactants HSO4- + H2PO4- SO42- + H3PO4 You should notice that this is really the same question as example 2. 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? 4.10 Read & Highlight Self Notes (p. 6 12) Problems Hebden # 38-46

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