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Volume of reactant?

  1. Jan 5, 2007 #1
    1. The problem statement, all variables and given/known data
    A certain volume of a solution of 0.800M sulfuric acid was added to solid magnesium carbonate, and the carbon dioxide evolved was passed through concentrated sodium hydoxide solution. When the reaction had ceased, the mass of this solution was found to have increased by 15.0g

    What volume of sulfuric acid must have been added?




    2. Relevant equations
    Basic stoichiometry


    3. The attempt at a solution
    H2SO4 + MgCO3 -> MgSO4 + H2O + CO2
    CO2 + NaOH -> NaHCO3

    Hence
    H2SO4 + MgCO3 -> MgSO4 + H2O + NaHCO3

    The extra weight comes from NaOH. Since the weight of the products had increased by 15g it must be due to NaOH. It comes out to .375 moles of NaOH.

    Since the mole ratio for every molecule is 1, there should be .375 moles of H2SO4 added. There are 0.8 moles of H2SO4 per litre so .375/.8=.47L or 470ml of H2SO4 but the answer at the back of the book suggest something else. I don’t know where I could have made my mistake.
     
  2. jcsd
  3. Jan 5, 2007 #2

    Gokul43201

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    I think you've misunderstood the question. CO2 is passed into a solution containing NaOH. The mass of this solution increases as a result of passing CO2 through it.
     
  4. Jan 6, 2007 #3

    So the product CO2 is passed into a solution containing NaOH?

    Or you are saying CO2 is in the reactants?

    Could you possibly who what you think is happening with a chemical formula? Where did the extra 15g come from?
     
  5. Jan 8, 2007 #4

    Borek

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    Mass of the NaOH solution increased when the carbon dioxide was absorbed by this solution.

    Carbon dioxide is produced in the first reaction (acid+carbonate) and consumed in the second reaction (separate solution of NaOH).

    Hopefully it is clear now.
     
  6. Jan 8, 2007 #5
    Does this mean I was correct?

    H2SO4 + MgCO3 -> MgSO4 + H2O + CO2
    CO2 + NaOH -> NaHCO3

    Hence
    H2SO4 + MgCO3 -> MgSO4 + H2O + NaHCO3

    So the answers at the back of the book were wrong?
     
  7. Jan 10, 2007 #6

    Borek

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    Forget about NaOH, it doesn't play any role here. NaOH solution part of the question is just a way of telling you what was the mass of the CO2 evolved. Insert this information into first reaction equation and you will be done.

    Looks to me like 426 is a correct answer. EBAS rulez ;)


    EBAS - equation balancer and stoichiometry calculator
     
  8. Jan 10, 2007 #7

    Gokul43201

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    Increase in the weight of what?

    (weight of NaOH solution after passing CO2) - (weight of NaOH before passing CO2) = 15g.

    Clear now?
     
  9. Jan 10, 2007 #8

    Now it's clear. The solution in that final sentence in the question was pointing to the solution containing NaOH. The 15g was the CO2 from the first reaction. It too some time for this question but I finally understood. Thanks.
     
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