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vera_ewing

  • one year ago

A weak acid with an initial pH of 3.2 was titrated with a strong base. 15 mL of 0.1 M NaOH was added to the acid to reach the equivalence point at a pH of 8.6. What would you expect the approximate pH of the analyte to be after the first 5 mL of 0.1 M NaOH was added? A. 5.1 B. 7.2 C. 3.4 D. 8.6

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  1. taramgrant0543664
    • one year ago
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    Do you have a guess of which one it is?

  2. taramgrant0543664
    • one year ago
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    I got 3.27

  3. vera_ewing
    • one year ago
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    So maybe it's C?

  4. taramgrant0543664
    • one year ago
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    I'm thinking so I don't think I messed up on my math would you like to know what I did?

  5. taramgrant0543664
    • one year ago
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    Ok so we have 15ml of 0.1M NaOH. We can find the moles of NaOH by multiplying the volume in liters (0.015L) by the molarity of 0.1

  6. taramgrant0543664
    • one year ago
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    So that means I have 0.0015moles of NaOH

  7. taramgrant0543664
    • one year ago
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    Then we can set up the ice table HA+NaOH ---> NaA+ H2O with the initial moles for NaOH as the 0.0015moles

  8. taramgrant0543664
    • one year ago
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    I am really bad at explaining this I followed what they did in this link http://chemwiki.ucdavis.edu/Analytical_Chemistry/Quantitative_Analysis/Titration/Titration_Of_A_Weak_Acid_With_A_Strong_Base

  9. vera_ewing
    • one year ago
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    Okay, hold on let me read it.

  10. taramgrant0543664
    • one year ago
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    Let me try this again and I'll let you know

  11. taramgrant0543664
    • one year ago
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    Now I'm getting an answer no where near anything my answer was just over one which does not make sense one bit!

  12. aaronq
    • one year ago
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    I don't think you need to do any math for the question since all the possible options are so far apart. Picture a titration curve |dw:1437179500727:dw| Initially, and for most of the curve, the slope is small, so we don't expect use changes in pH. If you used 1/3 of the moles that got you to 8.6 (which is a difference of about 5 from 3.2). so, 1/3 of 5 is 1.7, so 3.2 + 1.7\(\approx\)5 so I think 5.1 is reasonable

  13. aaronq
    • one year ago
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    sorry my graph is terrible and unrepresentative of whats going on lol

  14. taramgrant0543664
    • one year ago
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    that makes sense just to clarify though the 1/3 you get from the fact that it's 5mL out of the 15mL?

  15. aaronq
    • one year ago
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    yeah

  16. taramgrant0543664
    • one year ago
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    Sounds good it makes a lot more sense than the number I got and not having to do all that math is even better lol

  17. aaronq
    • one year ago
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    the math is often needed but it doesnt always have to be the first way to approach a problem.

  18. vera_ewing
    • one year ago
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    It was 3.4

  19. taramgrant0543664
    • one year ago
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    Good to know!

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