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Another example

Another example. What is the pH of 0.100 M citric acid?. What are you thinking…?. I am thinking absolutely nothing. I am waiting for you to tell me what to think. I’m thinking it must be equilibrium because that’s all we talk about.

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Another example

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  1. Another example Text 692019 and your message to 37607

  2. What is the pH of 0.100 M citric acid? Text 692019 and your message to 37607

  3. What are you thinking…? • I am thinking absolutely nothing. • I am waiting for you to tell me what to think. • I’m thinking it must be equilibrium because that’s all we talk about. • I’m thinking it must be equilibrium because it is asking about the pH Text 692019 and your message to 37607

  4. What is the pH of 0.100 M citric acid? Citric acid is H3C6H5O7 Now, I’m thinking… • Must be an acid • Must be diprotic • Must be triprotic • Must be a strong acid • Must be a weak acid Text 692019 and your message to 37607

  5. What is the pH of 0.100 M citric acid? Ka1=7.1x10-4 Ka2=1.7x10-5 Ka3=4.1x10-7 Now, I’m thinking: • Must be a weak acid • Must be a strong acid • Must be a triprotic weak acid • I don’t get paid to think, you do. Text 692019 and your message to 37607

  6. What is the pH of 0.100 M citric acid? Ka1=7.1x10-4 Ka2=1.7x10-5 Ka3=4.1x10-7 Now, I’m thinking: • 3 parts • 2 parts D. I’ve had about enough of your nonsense. Text 692019 and your message to 37607

  7. What is the pH of 0.100 M citric acid? Ka1=7.1x10-4 Ka2=1.7x10-5 Ka3=4.1x10-7 H3C6H5O7 (aq) + H2O (l) ↔ H3O+ (aq) + H2C6H5O7- (aq) H2C6H5O7- (aq) + H2O (l) ↔ H3O+ (aq) + HC6H5O72- (aq) HC6H5O72- (aq) + H2O (l) ↔ H3O+ (aq) + C6H5O73- (aq) Take them one at a time…or do I? Text 692019 and your message to 37607

  8. Text 692019 and your message to 37607

  9. Always try the assumption, we only have 30 seconds to lose. Assume x<<0.100 Text 692019 and your message to 37607

  10. Check close but no cigar Text 692019 and your message to 37607

  11. Text 692019 and your message to 37607

  12. Text 692019 and your message to 37607

  13. Start where the first one leaves off Text 692019 and your message to 37607

  14. Always try the assumption, we only have 30 seconds to lose. Assume x<<0.00808 Text 692019 and your message to 37607

  15. Check YAY! It works. Text 692019 and your message to 37607

  16. Start where the first one leaves off Text 692019 and your message to 37607

  17. Let’s take a moment for some deep reflection…. Did anything change during the second equilibrium? Yes, EVERYTHING changed. No, NOTHING changed. Some things changed, some things didn’t What are these “things” of which you speak? Text 692019 and your message to 37607

  18. Nothing changed… …to 2 sig figs. Which is a good thing! If it had changed, I would upset the first equilibrium! Text 692019 and your message to 37607

  19. First equilibrium Text 692019 and your message to 37607

  20. Second equilibrium They BOTH have to be satisfied if I’m truly at equilibrium. Let’s pretend this second equilibrium turned out differently… Text 692019 and your message to 37607

  21. Imaginary second equilibrium Now, look back at the first equilibrium…two of these compounds are the same! Text 692019 and your message to 37607

  22. Imaginary first equilibrium It can’t be at equilibrium anymore. The assumption that I can treat the equilibria separately relies on them not undoing each other. The bigger the K difference, the better. Otherwise, you have to solve both K’s simultaneously rather than consecutively. Text 692019 and your message to 37607

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