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B (Salters) F331 (Chemistry for Life) 22nd May 2015 [Official Thread] watch

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    (Original post by vuvuzela)
    Hess Law will blow up this year too.
    So will the three hydrocarbon processes

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    what do you mean by that?)
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    can someone explain the calculations of % on page 42 of the test bank pls
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    (Original post by TheLegalDealer)
    Divide the percentage of each atom which is basically its mass in the compound by its atmoic mass to find the moles of it

    Do this for all the atoms in the compound .Now find the ratio of the atoms by dividing each of the atoms moles by the moles of the atom that he smallest mole

    This would give you a ratio e.g. 2:2:1. Then just put the ratio of each atom in the formula e.g. C2H2O
    thanku
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    Can anyone explain Question 2d on the june 2014 paper its doing my head in
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    When given bond enthalpies, to work out enthalpy change, do you do products - reactants?
    or reactants - products?
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    (Original post by TheLegalDealer)
    Can anyone explain Question 2d on the june 2014 paper its doing my head in
    same here, still cant get the correct answer after like 10 attempts wtf, helppppppp
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    Sulfur is 10% of 1kg, so mass of sulfur is 100g, and Mr is 32.1
    Mol=mass/mr, so you can find moles of sulfur
    I assumed moles of sulfur is in the same ratio as mole of SO2 so calculated mole is mole of SO2
    Then you can rearrange formula so that mass= moles x Mr of S02, which gives you about 200g
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    (Original post by AAlice97)
    Sulfur is 10% of 1kg, so mass of sulfur is 100g, and Mr is 32.1
    Mol=mass/mr, so you can find moles of sulfur
    I assumed moles of sulfur is in the same ratio as mole of SO2 so calculated mole is mole of SO2
    Then you can rearrange formula so that mass= moles x Mr of S02, which gives you about 200g
    thank you so much !!!
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    can someone please explain hess law
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    (Original post by dansag)
    can someone please explain hess law
    If the starting and finishing points are the same the enthalpy change for a chemical reaction will always be the same regardless of the route it takes
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    Isn't it starting and finishing conditions must be the same not points ? how specific is the wording ?
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    (Original post by Obereicher)
    Isn't it starting and finishing conditions must be the same not points ? how specific is the wording ?
    Not that specific, the previous reply is accurate and would get you all marks

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    (Original post by buckeybarnes)
    can someone explain the calculations of % on page 42 of the test bank pls
    1.75% of 100g = 1.75g

    n=m/Mr

    1.75g/9= 0.19 moles (Be)

    100g-1.75g= 98.25g

    n= m/Mr

    98.25/63.25 = 1.55 moles (Cu)

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    (Original post by vuvuzela)
    Not that specific, the previous reply is accurate and would get you all marks

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    Name:  Screen Shot 05-21-15 at 10.02 PM 001.PNG
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    It would seem you do unfortunately
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    (Original post by Obereicher)
    Isn't it starting and finishing conditions must be the same not points ? how specific is the wording ?
    (Original post by vuvuzela)
    Not that specific, the previous reply is accurate and would get you all marks

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    No you have to have conditions, it says not to accept points even though that's what the revision guide says which is strange.
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    ^ i stand corrected. At least i know for tomorrow and hope it comes up

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    (Original post by chococup123)
    When given bond enthalpies, to work out enthalpy change, do you do products - reactants?
    or reactants - products?
    You do reactants- products

    If its negative= exothermic
    positive= endothermic
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    (Original post by vuvuzela)
    Hess Law will blow up this year too.
    So will the three hydrocarbon processes

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    What do u mean by the 3 hydrocarbon processes?

    Is it isomerism, cracking and reforming?
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    (Original post by shooting_stars)
    What do u mean by the 3 hydrocarbon processes?

    Is it isomerism, cracking and reforming?
    Yeah. Good luck all

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    Last min prep guys , what most likely to come up ??
 
 
 
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