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Homework Help: Neutralisation chemistry help

  1. Jun 7, 2006 #1
    can some one help me withe this?
    i want to neutralise a 400m3 of unknown solutions in pH 2 with sodium hydroxide. hw can i calculate the volume of alkaline needed? please help me!!!!!!!!!!!!!!!
     
  2. jcsd
  3. Jun 7, 2006 #2

    Hootenanny

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    HINT: Knowing the pH you can determine the hydrogen ion concentration.
     
  4. Jun 7, 2006 #3

    Borek

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    I hate such questions. You can't calculate anything without assuming that you have a solution of strong acid. Then (and only then) Hootenanny hint will work.
     
  5. Jun 7, 2006 #4
    Thank you

    Thank you! I solve it already by assuming it's a strong acid and got the answer. Thank you!
     
  6. Jun 8, 2006 #5

    Hootenanny

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    Ahh, yes thank you Borek. I had forgotten about week acids (never liked them anyway :grumpy: ) As Borek said, I think one would have to assume that the acid in question is a strong acid as no dissociation constant is given.
     
  7. Jun 18, 2006 #6
    Problems Again

    I solved for the heat of neutralization already, I thought, but now, I got the final temperature after reaction is 121.75 oC which I think is too big.

    I start with initial pH = 2 and final the conc H+ = 10^-(pH=2) then I find the mole by multipling the conc with the tank volume (400m3), the I find the mass by multiply it with MW.

    To neutralise 1 mole of H+, I need 1 mole of OH-, so I balance the mole of OH- needed with the mole of H+ I calculated justnow. The I got the mass and volume of NaOH needed to neutralize the pH 2.

    The heat of neutralization is -55.9 kJ/mol. The energy balance is (m.Cp.del_T)in = (m.del_H) + (m.Cp.del_T)out

    But since i use the initial temperature and reference temperature both also 25 oC, so the (m.Cp.del_T)in is cancelled. What left is only
    -(m.del_H) = (m.Cp.del_T)out

    The part that confused me here is what m should I use for these m.del_H and m.Cp.del_T. I obtained the answer stated ealier (121.75 oC) by using the mass for m.del_H is the mass of water produced and the mass for m.Cp.del_H is the mass of the total mass of NaOH+H2SO4 that reacted. Is this correct? If yes, is the temperature I got reasonable? If not, whats my mistake?
     
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