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JoannaBlackwelder

  • one year ago

What is the pH of a solution made by the addition of 0.34 mole of Na2HPO4 and 0.65 mole of NaH2PO4 and sufficient water to give a total volume of 1.2 L? The pKa of H2PO4 is 7.21.

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  1. Rushwr
    • one year ago
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    This makes up a buffer right?

  2. JoannaBlackwelder
    • one year ago
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    Yeah

  3. Abhisar
    • one year ago
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    \(\sf NaH_2PO_4 ----> Na^+ + H_2PO_4^-\) \(\sf Na_2HPO_4 ----> 2Na^+ HPO_4_2^- \)

  4. JoannaBlackwelder
    • one year ago
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    Right.

  5. Abhisar
    • one year ago
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    I am sorry, i don't know why the second latex is not working. pls bear with it.... Then we can see a case of bronsted acid-base \( \sf H2PO4^- + H2O --> HPO42^- + H3O^+\)

  6. Rushwr
    • one year ago
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    Na2HPO4 -----------> 2Na^+ + HPO4^-

  7. Abhisar
    • one year ago
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    We can use Henderson-Hasselbalch equation now for calculating the pH \(\sf pH = pK_a+log \frac{[conjugate~base]}{[acid]}\)

  8. JoannaBlackwelder
    • one year ago
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    Ah, I see! That makes sense. :-)

  9. JoannaBlackwelder
    • one year ago
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    Thank you!

  10. Abhisar
    • one year ago
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    Welcome c;

  11. Rushwr
    • one year ago
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    @Abhisar @JoannaBlackwelder What's the answer u get ?

  12. JoannaBlackwelder
    • one year ago
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    6.93

  13. Rushwr
    • one year ago
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    are u sure ?

  14. JoannaBlackwelder
    • one year ago
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    That's what I get. Why, what did you get?

  15. Rushwr
    • one year ago
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    I got 5.928

  16. Abhisar
    • one year ago
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    Ummm.. [H2PO4] = 0.65/1.2 (acid) [HPO4-] = 0.34/1.2 (conjugate base) I am getting around 7.05

  17. Rushwr
    • one year ago
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    Yeah I did it in the same way !

  18. Abhisar
    • one year ago
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    No, wait...

  19. Abhisar
    • one year ago
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    @JoannaBlackwelder is correct, pH = 6.9

  20. Abhisar
    • one year ago
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    We can use Henderson-Hasselbalch equation now for calculating the pH \(\sf pH = 7.21+log \frac{[0.28]}{[0.54]}\)

  21. Rushwr
    • one year ago
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    ooopss yes yes he is correct I have divided the acid moles by 12 !!!!!!!!

  22. JoannaBlackwelder
    • one year ago
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    :-) Thanks guys!

  23. Rushwr
    • one year ago
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    you get the same answer !!!! No I was wondering why my volume didn't cancel off . face palm

  24. Rushwr
    • one year ago
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    Soo dumb

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