1. Working with Acid-Base Equilibria Here we’ll examine the acid-base equilibrium that results when we mix two salts that have amphiprotic anions. Example 3 Starting With Salts

2. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. We’re given that the salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4.

3. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. And we’re asked to complete the equation for the equilibrium that is established.

4. We begin by taking the salt KHSO3 and writing the dissociation equation for it. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established.

5. It dissociates into K+ The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established.

6. And HSO3 minus. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established.

7. K+, an alkali metal cation, is a spectator ion. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. A spectator ion

8. So we eliminate it. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. A spectator ion

9. And all we’re left with the HSO3 minus. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established.

10. Now we take the other salt, Na2HPO4 and write its dissociation equation. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established.

11. It dissociates into 2 Na+ The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established.

12. And HPO4 2-, the monohydrogen phosphate ion. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established.

13. The Na+ ion, another alkali metal cation, is a spectator ion. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. A spectator ion

14. So we eliminate that. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. A spectator ion

15. Leaving us with only the monohydrogen phosphate ion. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established.

16. So we’ll move these two ions (click) so they become reactants… The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established.

17. in a new equilibrium equation. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established.

18. We’ll look up HSO3 minus on the acid table. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established.

19. We see that it is on both sides of the table, The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. Weak Acid Weak Base

20. So HSO3 minus is amphiprotic. It can act as an acid or as a base. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. Weak Acid Weak Base HSO 3 – is Amphiprotic

21. So we’ll jot that down here. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. Amphiprotic

22. Now, we’ll find HPO4 2- on the table The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. Amphiprotic

23. We see that it is also on both sides of the table, The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. Weak Acid Weak Base

24. So we can say that HPO4 2- is amphiprotic The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. Weak Acid Weak Base HPO 4 2– is Amphiprotic

25. Which we’ll make a note of here. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. Amphiprotic

26. Because these are both amphiprotic, we now have to determine which one will play the role of the acid. To do this we compare their strengths on the acid table. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. Which one will act as the acid?

27. We see that HSO3 minus is above HPO4 2- on the left side of the table, The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. Weaker Acid Stronger Acid

28. so HSO 3 – is a stronger acid than HPO 4 2– The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. Weaker Acid Stronger Acid HSO 3 – is a stronger acid than HPO 4 2–

29. Therefore, HSO3 minus will act as the acid on the left side. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. WrAWrB SrB SrA HSO 3 – is a stronger acid than HPO 4 2–

30. And the HPO4 2- will have to act as the base on the left side. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. WrAWrB SrB SrA

31. The acid will donate a proton to the base. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. WrAWrB SrB SrA H+H+

32. When HSO3– loses a proton it forms SO3 2-, the sulphite ion. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. WrAWrB SrB SrA H+H+

33. And When HPO4 2– gains a proton it forms H2PO4 –, the dihydrogen phosphate ion. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. WrAWrB SrB SrA H+H+

34. So we’ve now answered the first question. This is the equilibrium equation for this reaction. The salt potassium hydrogen sulphite, KHSO 3, is mixed with the salt sodium monohydrogen phosphate, Na 2 HPO 4. Complete the equation for the equilibrium that is established. WrAWrB SrB SrA The Equilibrium Equation

35. The next question we’re asked is whether the reactants or products are favoured at equilibrium. WrAWrB SrB SrA Are the Reactants or Products favoured at equilibrium?

36. To answer this we start by identifying the acids on the left side and the right side. Remember, the acid on the left side is HSO3 minus. WrAWrB SrB SrA Are the Reactants or Products favoured at equilibrium?

37. To find the acid on the right, we consider the reverse reaction. WrAWrB SrB SrA Reverse reaction Are the Reactants or Products favoured at equilibrium?

38. In the reverse reaction the H2PO4 minus loses 1 proton as it forms HPO4 2-. WrAWrB SrB SrA Reverse reaction Are the Reactants or Products favoured at equilibrium?

39. Therefore, H2PO4 minus is the acid on the right side. WrAWrB SrA Reverse reaction Are the Reactants or Products favoured at equilibrium?

40. Now we check these two acids on the left side of the acid table to determine which one is stronger and which one is weaker. WrAWrB SrA Which acid is stronger and which one is weaker? Are the Reactants or Products favoured at equilibrium?

41. We see that HSO3 minus is above H2PO4 minus on the left side of the table, Stronger Acid Weaker Acid Are the Reactants or Products favoured at equilibrium?

42. so HSO3 minus is the stronger acid H2PO4 minus is the weaker acid. Weaker Acid Stronger Acid Sr Wr Are the Reactants or Products favoured at equilibrium?

43. Which we’ll make a note of here in the equation. SrAWrB WrA SrA Are the Reactants or Products favoured at equilibrium?

44. Remember that equilibrium will always favour the side with the weaker acid. SrAWrB WrA SrA Equilibrium will always favour the side with the Weaker Acid. Are the Reactants or Products favoured at equilibrium?

45. And in this reaction, the products have the weaker acid, so equilibrium favours the products in this reaction. SrAWrB WrA SrA Equilibrium will always favour the side with the Weaker Acid. Equilibrium favours the Products Are the Reactants or Products favoured at equilibrium?

46. We’ve now answered the second question. Equilibrium favours the products in this case. SrAWrB WrA SrA Equilibrium favours the Products Are the Reactants or Products favoured at equilibrium?

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

48. We have determined that equilibrium favours the products in this reaction. SrAWrB WrA SrA For this reaction as written, which of the following is true? K eq 1 Equilibrium favours the Products

49. Which means we have a (click) greater amount of products than reactants at equilibrium. SrAWrB WrA SrA For this reaction as written, which of the following is true? K eq 1 Equilibrium favours the Products

50. So Keq, which is the ratio of products to reactants, SrAWrB WrA SrA For this reaction as written, which of the following is true? K eq 1

51. Is given by this expression. SrAWrB WrA SrA For this reaction as written, which of the following is true? K eq 1

52. And because equilibrium favours the products. SrAWrB WrA SrA For this reaction as written, which of the following is true? K eq 1 Equilibrium favours the Products

53. The Numerator is larger than the denominator SrAWrB WrA SrA For this reaction as written, which of the following is true? K eq 1 Numerator is larger than denominator Equilibrium favours the Products

54. So the value of Keq for this reaction is greater than 1. SrAWrB WrA SrA For this reaction as written, which of the following is true? K eq 1 > 1

55. And now we’ve answered the third question. K eq > 1 SrAWrB WrA SrA For this reaction as written, which of the following is true? K eq 1 > 1