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A chemistry question from top score

Discussion in 'DAT Discussions' started by Smooth Operater, May 4, 2007.

  1. Smooth Operater

    Smooth Operater don't bug "operatEr"! 5+ Year Member

    May 22, 2004
    what volume of HCl was added if 20 mL of 1 M NaOH is titrated w/ 1 M HCl to produce a pH = 2?

    The answer from top score is 20.4 ml.

    But how would you solve it? thanks!
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  3. BodybldgDoc

    BodybldgDoc Guest

    Jan 13, 2007
    In your closet
  4. Danny289

    Danny289 Member 2+ Year Member

    Dec 2, 2006
    :) For Qustion like this one you must now the concept, let me explain a little about that:
    first: Hcl and NaoH both are strong acid and base (k is very big number)

    second: they are monoporetic and mono hydroxide(actualy make it easier) that means, one H+ and one oH-naturalize each other.

    third(very important point): for both Molarity and Normality are equal(because the second point that I alredy mentioned) in other hand Mollar is 1, means Normality is 1 and if not , you must calculate the normality( recall from acid and base soultion ===> N= molarity x n)

    forth: concept of PH for acid ===> N=[H+]= 10
    now ve can attack the problom:

    for NaoH : V1=20 ml
    Cm(molarity)=0.1 ====> N1=0.1

    for Hcl : V2=?
    Cm=0.1 ==========> N2=0.1

    fina soultion after adding Acid and Base: -2
    PH= 2 ====> N(total)=10 = 0.01
    V(total)= V1 + V2= 20 + V2

    now, we can go for formula with knowing this concept that :we added acid and nutralized the base (N1V1=N2V2) and then add more acid and getting acidity solution(PH=2 means acidity solution) in other hand for sure we must add 20 cc acid and adding alittle more to get acidity solution.
    now we have formula
    N2V2-N1V1= NV=====> (0.1 x V2 )- (0.1 x 20 )= 0.01 x(20+ V2)
    beacause V total = V1+V2
    now find the V2 from above you will get this, in the end: V2=(20.2/0.99)

    and the answer wil be : 20.4 ml :)!:)
    good luck for ur DAT
  5. Danny289

    Danny289 Member 2+ Year Member

    Dec 2, 2006
    some misspelling about formulas plz check your books for relation between PH and Normality I couldn't fix it here:) :

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