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Edexcel - Chemistry Unit 2 - 4 June 2013 Watch

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    (Original post by Big-Daddy)
    What are you doing? The correct procedure is to find the percentage uncertainty in each measurement and then add them up since your combining the measurements. Which is 0.04/10+0.04/10=0.8%.

    Clearly you were thinking along the same lines are our examiners. I don't know if they have any clue what they're doing though; I was told I couldn't use the dot multiplier for multiplication and had to use a cross just because they "might not know enough maths", which I think is frankly ridiculous.
    Each measurement has uncertainty 0.4%. It follows that the overall uncertainty is 0.4%. Say you have two bags of marbles which you know each contain 5 +/- 1 marbles. The overall absolute uncertainty is 10+/-2 marbles, but the percentage uncertainty remains the same.
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    will melting temp of group 2 come up?
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    (Original post by maryam1996)
    Thank you so much , but what about if it's an elemenation reaction is it nucleophilic or electrophilic.
    Neither. It's "leaving group" elimination. Not that this will come up.
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    Do we need SN1 vs SN2? Or is SN1 the only one we ever need to know how to draw?

    (Original post by Masturchess)
    :confused:
    That's what I did, I think. I doubled the % error since you had to use the equipment twice; the 20 I got because you had to add 10cm to 10cm in a mixture, which would mean the total volume of the whole mixture was 20cm^3.
    My mistake, sorry! You're absolutely right.

    (Original post by metaltron)
    Each measurement has uncertainty 0.4%. It follows that the overall uncertainty is 0.4%. Say you have two bags of marbles which you know each contain 5 +/- 1 marbles. The overall absolute uncertainty is 10+/-2 marbles, but the percentage uncertainty remains the same.
    *Slaps head* What was I thinking? Add magnitude of uncertainties when adding or subtracting measurements, add percentage uncertainties when multiplying or dividing measurements.
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    (Original post by Priya08)
    thank you..okay I understand it now..one last question so is there such thing as permanent instantaneous dipole?
    Permanent dipoles only form between polar molecules : the delta negative and delta positive have electrostatic attraction.
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    PS Reviewer
    Is this exam in the afternoon?

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    (Original post by James A)
    Is this exam in the afternoon?

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    Yes
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    (Original post by Big-Daddy)
    Do we need SN1 vs SN2? Or is SN1 the only one we ever need to know how to draw?
    I think it's came up before to draw the intermediate for a primary and a tertiary halogenoalkane or something similar so i think we need to know them. Sn1 has the cation and Sn2 has the 2 partial/temporary bonds to the halide and nucleophile
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    Do we meed to know the catalysts? If anyone knows help is appreciated cheers as in the irdium iodide etc


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    As a general note, double check your answers to multiple choice questions when you ask them, twice it has happen that the original asker gave the wrong 'answer'. It's just going to confuse others, who will confuse you even more...


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    (Original post by ASStudent)
    Do we meed to know the catalysts? If anyone knows help is appreciated cheers as in the irdium iodide etc


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    nope i guess they might just ask it's function how it would it work.
    they wold probably give it in question.
    remember Cl radical and NO are catalyst too.
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    (Original post by geor)
    We have to know phosphorus?!
    I'm going to memorize it tomorrow morning just in-case, but what do you think ? :confused: There's way too much to remember I think I'll be getting section B & C out of the way first thing !
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    (Original post by marz1994)
    will melting temp of group 2 come up?
    may be to compare Carbonates or Nitrate regarding thermal stability, just to give u an idea wich has more melting temp. mostly they'll gv in the paper.
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    Hi, can someone please explain to me why the c-Br bond is more electronegative than the C-I bond. I also don't understand why thermal stability of metal carbonates increases down group 2 even-though that as the cation ion gets larger down the group doesn't that make it less stable as it can easily lose electrons now as it has more sheilding and is further away from the nucleus as it has a reduced polarising power. I'm quite confused,
    Thank you
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    (Original post by geor)
    We have to know phosphorus?!
    It's just P4 + 6X2 -> 4PX3, P4 + 10X2 -> 4PX5. I can't see anything involving O coming up but just bear in mind that POX3 is not uncommon.

    Didn't you get Gold in the U6 Olympiad? This shouldn't be hard
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    Why are HCFCs less stable that CFCs?
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    (Original post by posthumus)
    I'm going to memorize it tomorrow morning just in-case, but what do you think ? :confused: There's way too much to remember I think I'll be getting section B & C out of the way first thing !
    Every phosphorous reaction that can come up, can be worked out on the spot. As far as I know, POX3 comes from P4 + 6X2 + 2O2 -> 4POX3.
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    (Original post by geor)
    Shush nowww But thanks.
    Are you doing this exam?
    Yah.
    I wish now that I had revised more for the exam itself. I'll be applying for Chemistry but with better scores in Physics and Maths at this rate
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    http://www.edexcel.com/migrationdocu...e_20110120.pdf Q's 7c, 11d, 6b
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    (Original post by geor)
    Haha - brilliant! Yeah I was aiming for the full UMS but the grade boundaries are just so ridiculous, have to be so precise.
    I'm planning to apply for chemistry too! Where are you looking at?
    Depending on my scores (in Chemistry, Physics & Maths) either Cambridge or Oxford, as well as Durham (NatSci), Imperial (Chemistry) and Nottingham (NatSci). Not sure where else atm. What about you?
 
 
 
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