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Chem questions

Discussion in 'DAT Discussions' started by supera, Jul 21, 2011.

  1. supera

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    These are GC/OC questions from 2009 ADA sample

    1.What is Heat of formation reaction for solid CaCO3?
    (I took online version and for some reason this one's choice is not showing up)

    a. Ca(OH)2(aq) + 2H2CO3(aq) → CaCO3(s) + H2O(l)
    b. CaO(s) + CO2(g) → CaCO3(s)
    c. Ca2+(aq) + CO32–(aq) → CaCO3(s)
    d. Broken IMAGE (this online version is pissing me off:mad:)
    e. 2CaCO3(s) →2Ca(s) + 2C(graphite) + 2O3(g)

    I am sorry that my questions quality is so bad, I am just not sure what is heat of formations for solid CaCO3

    2. Which can be used to separate non-volatile substances?

    a. Thin-layer chromatography
    b. Gas-liquid chromatography
    c. Sublimination
    d. Distillation
    e. Steam distillation

    What's the answer for this and why?
     
    #1 supera, Jul 21, 2011
    Last edited: Jul 21, 2011
    Justdontblink likes this.
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  3. mh0000

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    heat of formation is the enthalpy change for the formation of a substance from its elemental components.

    C(graphite) + Ca(s) + O2(g) ---> CaCO3 (s)
    [not balanced, I have to leave asap, sorry]
    PS: heats of formations are alaways negative.
     
  4. supera

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    Thank you mh0000!
    Does anyone have a idea for my second question?
     
  5. AlbinoPolarBear

    7+ Year Member

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    Non-volatile means it doesn't turn into a gas.

    Of all the choices, only a) Thin-layer chromatography, which separates liquids with different polarities, can be used.

    Everything else requires the substance to turned into a gas (volatile).
    Gas-liquid chromatography (dead give away, has gas in the name).
    Sublimation (solid to gas).
    Distillation (liquid to gas).
    Steam distillation (liquid to gas, with help of steam).
     
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  6. supera

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    Thanks AlbinoPolarBear! appreciate your help!
     
  7. crax

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    would anyone be able to explain their approach to solving number one please?
     
  8. rpatel8

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    A heat of formation reaction is forming it from everything its elemental form. So here we are given CaCO3. We start by putting Ca(s), C(graphite), and O2(g) on the reactants side. Then you balance the equation to get :

    2Ca(s) + 2C(graphite) + 3O2(g) -----> 2CaCO3(s)
     

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