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Problem involving "normality" of a solution

  1. Jan 11, 2015 #1

    s3a

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    1. The problem statement, all variables and given/known data
    Question:
    A 1 N solution of ##H_2SO_4## will contain approximately 0.5 mol of the compound per liter of solution.

    (a) True

    (b) False

    Correct answer:
    (a) True

    2. Relevant equations
    Normality = GramsOfSolute/(AmountOfSolvent*EquivalentWeight)

    EquivalentWeight = MolecularWeight/Valence

    I don't know how to find the valence

    3. The attempt at a solution
    I watched this ( ) and this ( ) and also found this ( http://www.wikihow.com/Calculate-Normality ).

    I'm assuming hydrogen is the solute, but could someone please tell me how I'm supposed to know this?

    So, 1 mole of H amounts to about 1.01 g of H, so 2 moles of H amounts to about 2.02 g of H.

    Then, Normality = (2.02 g of H) / (2 mol of H * EquivalentWeight), and I don't know how to proceed from here.

    Could someone please help me understand how to get the correct answer?
     
  2. jcsd
  3. Jan 11, 2015 #2

    Bystander

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    There is NO way you can know this without context. "Normality" is an archaic, obsolete, outmoded, useless, ambiguous, concentration scale. Given the answer, you know that the problem is referring to an acid-base titration situation. If sulfuric acid is present in solution at 0.5 mole per liter (given in the problem statement) you know you have a 0.5 molar solution. "Valence" in this case is another horribly misused word, but they're asking how many hydrogen ions can you neutralize per mole of sulfuric acid.

    Normality for acid-base titration purposes for polyprotic acids equals molarity times the number of protons in the acid.
    If you were doing a barium sulfate precipitation with this same solution, normality would be based on the sulfate concentration, and be 0.5
     
  4. Jan 13, 2015 #3

    s3a

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    Thanks for the response; it's nice to know that this is archaic stuff ;), but I still need to cover it.

    Okay, so, let's say the question was instead written as follows (where the word acid is the most important addition).:
    A 1 N solution of sulfuric acid, ##H_2SO_4##, will contain approximately 0.5 mol of the compound per liter of solution.

    (a) True

    (b) False

    Could it then be expected that I am able to deduce that hydrogen is the solute?

    What if it's monoprotic? Does that formula no longer apply? Also, what are the units for that formula? (mol/L for molarity of the solution) * (g/mol for molar mass of the protons from all the Hydrogen atoms - does this make sense?) = (g/L for normality of the solution)? (Or kg instead of g if using SI units.)
     
    Last edited by a moderator: Jan 13, 2015
  5. Jan 13, 2015 #4

    Borek

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    Staff: Mentor

    Hydrogen is not a solute. Acid is. On dissociation acid produces hydronium and an anion, so the hydronium is present in the solution.

    For monoprotic acid normality equals molarity, that's all (so the formula works, just with the number of protons being equal to 1).

    And the unit is chemical equivalent/L.
     
  6. Jan 14, 2015 #5

    s3a

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    What's another way of representing the chemical equivalent unit by using other units?

    For example, in the case of Newtons, N, we can say that 1 N = 1 kg * m/s^2.
     
  7. Jan 14, 2015 #6

    Borek

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    Staff: Mentor

    Equivalent is related to mole, so you can try to express it as mole/n, where n is number of protons (or electrons, or even something else, there are several definitions of what the equivalent is). N has no units, it is just a fraction. But digging that deep is a waste of time IMHO.
     
  8. Jan 14, 2015 #7

    s3a

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    I'm not looking for every definition of what an equivalent is. Just one that, in addition to being correct, is intuitive to me.

    So, when you say the equivalent unit can be given as mole/n, generally speaking, we're talking about a mole of what and the number of protons of what? Is it mole of the solution and number of protons whose containing atoms are ionized? Please tell me if I'm using any term incorrectly.

    Also, sorry for being pedantic, but digging deep like this does help me, in general.
     
  9. Jan 15, 2015 #8

    Borek

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    Staff: Mentor

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