1. Working with Acid-Base Equilibria When a weak acid and a weak base are mixed, an equilibrium is always established. Example 2 Starting With Amphiprotic Anions

2. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. We’re told that the hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –.

3. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. And we’re asked to complete the equation for the equilibrium that is established.

4. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. We start by writing the formulas for the two given reactants, HC2O4 – and HSO3 –. We find HC2O4 minus on the acid table…

5. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. And we see that its on both sides of the table so it can act as either an acid or a base. Weak Acid Weak Base

6. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. Therefore, HC2O4 minus is amphiprotic Weak Acid Weak Base HC 2 O 4 – is Amphiprotic

7. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. We’ll label it as amphiprotic here. Amphiprotic

8. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. Now we’ll look up HSO3 minus on the table… Amphiprotic

9. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. We see that HSO3 minus is also on both sides of the table. Weak Acid Weak Base

10. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. So it is also amphiprotic Weak Acid Weak Base HSO 3 – is Amphiprotic

11. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. We’ll label it as amphiprotic here. Amphiprotic

12. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. Because HC2O4 minus is amphiprotic, it is able to act either as an acid or as a base. Amphiprotic Can act as an acid or a base

13. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. And because HSO3 minus is amphiprotic, it is also able to act either as an acid or as a base. Amphiprotic Can act as an acid or a base

14. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. So the question is, which one of these will act as the acid in the forward reaction? We find out by locating both of these on the left side of the acid table and comparing their strengths. Which one will act as the acid?

15. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. Locating them, we see that HC2O4 minus is a stronger acid than HSO3 minus. Weaker Acid Stronger Acid

16. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. The stronger acid of the two, the HC2O4 minus, is the one that will play the role of the acid. Weaker Acid Stronger Acid HC 2 O 4 – is stronger, so it will act as the acid

17. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. So we’ll label HC2O4 minus as the acid on the left side of the equation. WrAWrB SrB SrA

18. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. And the HSO3 minus will have to play the role of the base. WrAWrB SrB SrA

19. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. A proton is transferred from the acid to the base. WrAWrB SrB SrA H+H+

20. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. Because HC2O4 minus loses a proton, it will form C2O4 2-. WrAWrB SrB SrA H+H+

21. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. And Because HSO3 minus gains a proton, it will form H2SO3. WrAWrB SrB SrA H+H+

22. The hydrogen oxalate ion, HC 2 O 4 –, is mixed with the hydrogen sulphite ion, HSO 3 –. Complete the equation for the equilibrium that is established. So we’ve now answered the first question. This is the equilibrium equation. WrAWrB SrB SrA The Equilibrium Equation

23. Will Reactants or Products be Favoured at Equilibrium? The next question is, “Will reactants or products be favoured at equilibrium?” WrAWrB SrB SrA Will Reactants or Products be Favoured at Equilibrium?

24. To answer that, we start by identifying the acid on the left side and the acid on the right side. WrAWrB SrB SrA Identify the acid on the left side and the acid on the right side.

25. Will Reactants or Products be Favoured at Equilibrium? We already know that the acid on the left side is HC2O4 minus. WrAWrB SrB SrA

26. Will Reactants or Products be Favoured at Equilibrium? To find the acid on the right, we consider the reverse reaction. WrAWrB SrB SrA Reverse reaction

27. Will Reactants or Products be Favoured at Equilibrium? As the reverse reaction occurs, the H2SO3 is the species that loses a proton. WrAWrB SrB SrA Reverse reaction

28. Will Reactants or Products be Favoured at Equilibrium? So H2SO3 is the Acid on the right side. WrAWrB SrB SrA Reverse reaction

29. Will Reactants or Products be Favoured at Equilibrium? Now we focus on the two conjugate acids in this equilibrium, HC2O4 minus on the left, and H2SO3 on the right. We look them both up on the Left side of the acid table so see which one is stronger. WrAWrB SrB SrA

30. Will Reactants or Products be Favoured at Equilibrium? We can see that, of these two acids, H2SO3 is the stronger acid and HC2O4 minus is the weaker acid. Stronger Acid Weaker Acid

31. Will Reactants or Products be Favoured at Equilibrium? So we can label H2SO3 as the stronger acid an HC2O4 minus as the weaker acid in our equilibrium equation. WrAWrB SrB SrA

32. Will Reactants or Products be Favoured at Equilibrium? Now we recall that equilibrium will always favour the side with the Weaker acid. WrAWrB SrB SrA Equilibrium will always favour the side with the Weaker Acid.

33. Will Reactants or Products be Favoured at Equilibrium? Because the weaker acid is on the reactant side, we can say that reactants are favoured at equilibrium. We have now answered the second question. WrAWrB SrB SrA Reactants are favoured

34. Now we’ll look at relative amounts of reactants and products present at equilibrium. Because reactants are favoured,(click) there are more reactants than products at equilibrium. Reactants are favoured

35. Or we can say that reactant concentrations are higher than product concentrations at equilibrium. Reactant concentrations are higher than product concentrations.

36. The last question we’re asked is whether the value of Keq for this reaction is less than 1 or greater than 1. For this reaction as written, which of the following is true? K eq < 1 K eq > 1 For this reaction as written, which of the following is true? K eq 1

37. Remember that Keq is the ratio of the concentrations of the products to the concentrations of reactants at equilibrium. For this reaction as written, which of the following is true? K eq 1 Ratio of [Products] to [Reactants]

38. In this particular reaction we had determined that the reactants are favoured. For this reaction as written, which of the following is true? K eq 1 Reactants are Favoured

39. Inserting the products and reactants into the Keq expression, For this reaction as written, which of the following is true? K eq 1

40. And knowing that reactants are favoured, we see that the numerator is smaller than the denominator. For this reaction as written, which of the following is true? K eq 1 Numerator Denominator Reactants are Favoured

41. So the value of Keq for this reaction is less than 1. So we have now answered the last question. For this reaction as written, which of the following is true? K eq 1 Reactants are Favoured < 1

42. Remember when reactants are favoured, the value of Keq is always less than 1. For this reaction as written, which of the following is true? K eq 1 Reactants are Favoured < 1