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Buffer solutions

  1. Jul 5, 2016 #1

    TT0

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    1. The problem statement, all variables and given/known data
    Screen Shot 2016-07-05 at 5.01.31 PM.png

    2. Relevant equations


    3. The attempt at a solution
    From what I know, to make buffer solutions you need a weak acid or base and it's salt. Non of the options has this. What am I missing?

    Cheers!
     
  2. jcsd
  3. Jul 5, 2016 #2

    Borek

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    Staff: Mentor

    What is left after the reaction?
     
  4. Jul 6, 2016 #3

    TT0

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    For reaction 1, the products are: Cl-, NH4+, NH3, H+ (as HCl is strong acid while ammonia is weak base)
    For reaction 2, the products are: Na+, H2O, NO2- (NaOH is strong while nitrous acid is weak. No HNO2 because the H+ will react to form water so equilibrium will shift to the right in equilibrium HNO2 → H+ + NO2-)
    For reaction 3, the products are: NH3, NH4+, HNO2, NO2- (both are weak)

    Reaction 3 is probably creates a buffer solution as they can accept or donate protons and the equilibrium will shift.
    If acid was added to reaction 2, the NO2- will turn to nitrous acid but if base was added, nothing will happen, so not a buffer solution.
    If acid was added to reaction 1, the equilibrium NH3 + H+ ↔ NH4+ will shift to the right and if base was added, the equilibrium will shift to the left so it is a buffer solution.

    Answer is D.

    Are my explanations correct?

    Cheers!
     
  5. Jul 6, 2016 #4

    Borek

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    Staff: Mentor

    Nope, you need a comparable amounts of conjugate acid and base for the buffer to exist.
     
  6. Jul 8, 2016 #5

    TT0

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    I see, I change my mind on reaction 2. There will be around 0.5 M of HNO2 and NO2- so it will be a buffer solution. So then the answer is E?

    Cheers!
     
  7. Jul 9, 2016 #6

    Borek

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    Staff: Mentor

    What is present after the reaction in the 3rd mixture?
     
  8. Jul 12, 2016 #7

    TT0

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    NH3, NH4+, HNO2, NO2-
     
  9. Jul 12, 2016 #8

    Borek

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    Staff: Mentor

    In what (approximate at least) concentrations?
     
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