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Homework Help: Molarity to grams

  1. Apr 13, 2010 #1
    1. The problem statement, all variables and given/known data
    Calculate the mass (in grams) of KHP required to react completely with the NaOH in 35 mL of 0.100M NaOH.

    KHP = KHC8H4O4(aq)
    molar mass of "KHP"= 204.2 g/mol
    2. Relevant equations

    This is a double replacement reaction of the acid-base neutralization type. In other words the K will be replaced with Na and the product will have H2O in the mix.

    3. The attempt at a solution

    It wants KHP in grams.

    g/m * m/L*

    See this is where I get lost. I'm sure its something simple. Also m/l = M. Just to make sure, if I have the volume (L) and the Molarity (M) to get the moles, the only thing i have to do is multiple the volume by the molarity?
     
  2. jcsd
  3. Apr 13, 2010 #2

    Borek

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    Staff: Mentor

    You got it wrong, K won't be replaced by Na.

    Try to write balanced reaction equation.

    Calculate moles first, then convert to grams. But you need balanced reaction equation first.

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    methods
     
  4. Apr 13, 2010 #3
    thank you for the reply and groovy hair BTW. :cool: My mistake, it was the H. I had to look it over again.

    KHC8H4O4(aq) + NaOH --> NaKC8H4O4 +H2O(l)

    I looked over this a couple times and it looks balanced to me.

    There is ...

    1 Na -> 1 Na
    1 K -> 1K
    H+H4+H = 6 ->H4+H2= 6
    C8 = C8
    O4+O = 5 -> O4+O = 5

    By chance is the problem:

    mol NaOH x mol KHP/mol NaOH x g KHP/mol KHP ???
     
    Last edited: Apr 13, 2010
  5. Apr 13, 2010 #4

    Borek

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    Staff: Mentor

    Reaction is OK - you don't have to check separately if every element is balanced, note that C8H4O42- is present on both sides, it is not much different from other groups (like SO42-) that are almost always treated as a whole.

    Yes, that's OK - but it is obvious now, after you have checked what is stoichiometry of the reaction. 1 mole of KHP reacts with 1 mole of NaOH.

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    methods
     
  6. Apr 13, 2010 #5
    Thank you. Last question would be about converting KHP to moles.

    I don't understand how to make a conversion question for that.
     
  7. Apr 13, 2010 #6

    Borek

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    Staff: Mentor

    Please elaborate, no idea what you mean.

    You can easily calculate number of moles of NaOH, you know they react 1:1, so number ofmoles of KHP must be identical to number of moles of NaOH.

    See also

    http://www.titrations.info/titration-calculation
     
  8. Apr 13, 2010 #7
    Calculate the amount(in moles) of KHP required to react completely with the NaOH in 35 mL of 0.100M NaOH.

    This is what I was referring to.
     
  9. Apr 13, 2010 #8

    Borek

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    Staff: Mentor

    Read my previous post, this is a simple stoichiometry.

    Unless you have no idea what reation equation means. If so, please see how to read reaction equation.

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    methods
     
  10. Apr 13, 2010 #9
    I am a beggining chemistry student and we have only had a couple lectures on stoichiometry and molarity. I will check out your site for further information.dziękuję
     
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