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Homework Help: Molarity question

  1. Jan 4, 2008 #1
    1. The problem statement, all variables and given/known data
    another satII chem question:
    Forty grams of sodium hydroxide is dissolved in enough water to make 1 liter of solution. What is the molarity of the solution?
    (A) 0.25 M
    (B) 0.5 M
    (C) 1 M
    (D) 1.5 M
    (E) 4 M

    2. Relevant equations

    Molarity = (number of moles of solute) / (1 L of solution)

    3. The attempt at a solution
    well, i converted 40 g of NaOH to moles so...
    40 g NaOH x (1 mol NaOH) / (40 g NaOH)= 1 mol
    Molarity = (1 mol) / (1 L) = 1 M

    but the book says the answer is (A) & their explanation is...
    NaOH is 40 g/mol. 10 g is 10/40 or 0.25 mol in 1 L or 0.25 M

    i have no idea, how they're getting the 10.
    and would appreciate any help at alll.

    thank you so much guys :biggrin:

    also; if anyone knows how to insert division signs to make the presentation look ANY better, because right now it looks messy!...i was trying to use the underline thing, but the formatting got all messed up!
  2. jcsd
  3. Jan 4, 2008 #2
  4. Jan 4, 2008 #3


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    40 gr in 1 liter gives 1 mol NaOH solution, I think the book is wrong because I can't see any reason for using 10 gr that is not given in the question.
  5. Jan 4, 2008 #4
    thanksyou :)

    thank you so much guys!
    i was feeling a little down, as to why i wasn't getting this little molarity problem.
    and two physics-forum people agreeing with me makes me feel a whole lot better.
    thanks once again! :biggrin:
  6. Jan 4, 2008 #5


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    Science Advisor
    Homework Helper
    Gold Member

    Do you think it is possible that someone penciled in the '4' in 40 from what was originally a '1'? If so, that's a pretty dirty trick.
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