The Solutions and Fin

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The combustion of benzene (C6H6), which is a hydrocarbon hexagonal ring, is 2C6H6 9(l)+ 15O2(g) ---> 12CO2 (g)+ 6H2O(g): two moles of benzene when reacted with fifteen moles of oxygen GAS will produce twelve moles of carbon dioxide and six moles of water vapor.
Benzene ring
Benzene ring

Note the discrepancies: 54 moles of CO2 were created and 1.824 kg of EXCESS oxygen gas in respects to the benzene combustion was consumed! Using those two bits of information you could find out the formula of the substance.

  1. Find out the combustion equation of the substance.
    • a) 54 moles of CO2 were produced when only twelve should of been. That means the substance combusted to produce 42 moles of CO2.
    • b) 1.824 kg O2 * 1000 grams O2 = 1824 grams O2
      .......................................................................................................................1.. kg O2
      • i) 1824 grams O2 * 1 mole O2 = 57 moles O2
        ................................................. 32 g O2
      • ii) Deduce that since 57 moles of excess O2 were used, that means it was consumed by the combustion reaction of the poison.
    • At this point the equation is aCaHbOc + 57 O2(g) --> 42CO2(g) + dH2O(g)
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  2. Solve for the coefficients of the poison; this is the tricky, tricky, tricky, part.
    • Since the law of conservation of mass dictates that matter can not be created nor destroyed, that means 42 moles of Carbon were reactants.
      • aC42HbOc + 57 O2(g) --> 42CO2(g) + dH2O(g)
    • Since there are 42 moles of C in the poison, 42 moles C * 12.01 grams C (the molar mass of Carbon) = 504.42 grams C.
      .................................................................................................................................................................................................................................................................................................................................................       1 moles C
    • Since 504.42 grams C is 79% of the chemical formula, you can find out the other subscripts by setting up ratios.
      • 504.42 g = b (1.008 [molar mass of H]) grams
        ..........0.79.........................................................................................................0.17..
        1. Cross multiply: 85.7514 = 0.79(1.008b)
        2. Isolate b: 85.7514/(0.79*1.008)
        3. b = 67.78 => 68
          • aC42H68Oc + 57 O2(g) --> 42CO2(g) + dH2O(g)
      • 504.42 g = c (16.00 [molar mass of O]) grams
        ..........0.79.........................................................................................................0.10..
        1. Cross multiply: 50.442 g = 0.79(16c)
        2. Isolate c: 50.442 / (.79*16)
        3. c = 3.99 => 4
          • aC42H68O4 + 57 O2(g) --> 42CO2(g) + dH2O(g)
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............3.Solve for d and a
    • Since there are 68 moles of H in the reactant side, there has to be 68 moles of H in the product side. To achieve that, d must equal 34, since 34 moles of H2 equals 68 moles of H.
    • Finally a = 1 since everything balances out.
      • That means the equation is C42H68O4 + 57 O2(g) --> 42CO2(g) + 34H2O(g)
..........4. Using the equation from problem 1 and the fact that 6 moles of water are created in the combustion of benzene, the creation 40 moles of water will validate ... .......... .......... .......... .............your .answer.

..........5.Find the molecular formula to find out the substance is actually C21H34O2

    • To find molecular formula, 1)you must divide the actual mass by the empirical mass: (318.482 / 636.964 => .5)
    • 2) Then multiply the subscripts by that number (42 / 2 = 21, 68 / 2 = 34, 4 / 2 = 2)
The True Ending:


Investigator
Investigator
The lab results came back in; the lab that processed the ivy sample from your house returned an urushiol sample with 21 carbons, 34 hydrogens, and 2 oxygens thus matching the sample solved by our ace chemist. Question now remains, why and where did you come up with such an idea? If we didn't have such an apt chemist, you would of certainly gotten away.
Samantha Lily
Samantha Lily
Fine, you got me. I was just so mad at Ryan for dumping me! I didn't want to escalate to killing him, just getting back at him. I saw on T.V. once that two people smoked poison sumac and died because they had an allergic reaction. I used a lot less than the guys on the television did, but I honestly didn't know that it would kill Ryan! Plus, using a plant would frame Melisa, I hated her as much as I was mad at Ryan.
Investigator
Investigator
Well, you're going away for a long time. Maybe you can find another boyfriend once your out of jail in a couple of decades.