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    Wow you've done so many exams! My first exam is on Tuesday and it's biology so yeah I'm feeling quite nervous.

    In my chem mock we were given the pink booklet and it was pretty much the same as the one I use at home: http://www.edexcel.com/migrationdocu...et_Issue_2.pdf

    I'm not sure of that helps you at all! But good luck once again, keep going strong!
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    What was the pH when 24.95 cm3 NaOH(aq) had been added to 25of 1.00 mol dm-3 cm3 of 1.00 mol dm-3 HCl(aq).

    Can someone work this out and tell me what they get- I get 4.3 do u guys agree?
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    (Original post by Dolphino)
    Wow you've done so many exams! My first exam is on Tuesday and it's biology so yeah I'm feeling quite nervous.

    In my chem mock we were given the pink booklet and it was pretty much the same as the one I use at home: http://www.edexcel.com/migrationdocu...et_Issue_2.pdf

    I'm not sure of that helps you at all! But good luck once again, keep going strong!
    Thanks, but this is the one I had too The pink one I received in Jan was totally different... and one of the compounds was such a pain to find ! (literally took like over 5 minutes to figure it out, because I was trying to make do with other data & figure out the standard entropy myself).

    And thanks, best of luck to you too I think it's about time I move onto past papers!

    (Original post by Dolphino)
    What was the pH when 24.95 cm3 NaOH(aq) had been added to 25of 1.00 mol dm-3 cm3 of 1.00 mol dm-3 HCl(aq).

    Can someone work this out and tell me what they get- I get 4.3 do u guys agree?
    Assuming the concentration of NaOH is also 1.00 mol dm-3 ... I got 4.3 as well
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    (Original post by posthumus)

    Assuming the concentration of NaOH is also 1.00 mol dm-3 ... I got 4.3 as well
    Could you please explain how you did it?
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    (Original post by Dolphino)
    What was the pH when 24.95 cm3 NaOH(aq) had been added to 25of 1.00 mol dm-3 cm3 of 1.00 mol dm-3 HCl(aq).

    Can someone work this out and tell me what they get- I get 4.3 do u guys agree?
    (Original post by SKK94)
    Could you please explain how you did it?
    Sorry I think I've done it wrong Just realized I logged the moles of H+

    Anyway... find moles of both OH- & H+ ... find the difference in moles... this difference is the extra H+ making the solution acidic. I got 5 x 10^-5 here. Now I negative logged this when I am supposed negative log the concentration.

    The concentration = mole / volume = 5 x 10^-5 / 0.02495 + 0.025 = 1 x 10^-3 moldm^-3

    pH= 3
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    (Original post by posthumus)
    Sorry I think I've done it wrong Just realized I logged the moles of H+

    Anyway... find moles of both OH- & H+ ... find the difference in moles... this difference is the extra H+ making the solution acidic. I got 5 x 10^-5 here. Now I negative logged this when I am supposed negative log the concentration.

    The concentration = mole / volume = 5 x 10^-5 / 0.02495 + 0.025 = 1 x 10^-3 moldm^-3

    pH= 3
    Yes that's what I realised I've done wrong too!
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    (Original post by posthumus)
    Sorry I think I've done it wrong Just realized I logged the moles of H+

    Anyway... find moles of both OH- & H+ ... find the difference in moles... this difference is the extra H+ making the solution acidic. I got 5 x 10^-5 here. Now I negative logged this when I am supposed negative log the concentration.

    The concentration = mole / volume = 5 x 10^-5 / 0.02495 + 0.025 = 1 x 10^-3 moldm^-3

    pH= 3
    Thank you!
    I kept using the difference in concentration of OH- and H+
    xD
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    does anyone wanna revise?
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    (Original post by AS01)
    does anyone wanna revise?
    What indicator would you use for weak acid & weak base titration ?
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    (Original post by posthumus)
    What indicator would you use for weak acid & weak base titration ?
    yay! one is here
    you don't coz the vertical section of graph is rarely even there.

    give an example of addition elimination reaction of acyl chloride.
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    (Original post by AS01)
    yay! one is here
    you don't coz the vertical section of graph is rarely even there.

    give an example of addition elimination reaction of acyl chloride.
    Yup ! Now I know your well prepared, aha

    Acyl chloride + H2O ??

    Explain why LiAlH4 does not reduce the C=C bond
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    (Original post by posthumus)
    Yup ! Now I know your well prepared, aha

    Acyl chloride + H2O ??

    Explain why LiAlH4 does not reduce the C=C bond
    yup!
    coz its not polar.

    How GC work?
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    (Original post by AS01)
    yup!
    coz its not polar.

    How GC work?
    Hehe, your evil... I told you that it's the one I need to go through!

    But tell me if I've missed out any points:
    - if Liquid is vaporized and carried by the mobile phase (which is an inert gas I think)
    - pushed through with pressure and through stationary phase
    - Stationary phase consists of solvent absorbed onto solid
    - The interaction between mobile & stationary phase determine how much time it takes for the mobile phase to go through, this is called the retention time.
    - Retention time is unique to specific compounds, look up what type of compound it is using data resources.
    - Structure can also be found using Mass or IR spectroscopy

    This is also useful to purify some liquids?
    I think I may have mixed HPLC with GC here

    Explain with reference to lattice & hydration enthalpies why hydroxides are more soluble as you go down group 2 & the opposite is the case for group 2.

    EDIT: opposite is the case for sulfates, sorry
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    (Original post by posthumus)
    Hehe, your evil... I told you that it's the one I need to go through!

    But tell me if I've missed out any points:
    - if Liquid is vaporized and carried by the mobile phase (which is an inert gas I think)
    - pushed through with pressure and through stationary phase
    - Stationary phase consists of solvent absorbed onto solid
    - The interaction between mobile & stationary phase determine how much time it takes for the mobile phase to go through, this is called the retention time.
    - Retention time is unique to specific compounds, look up what type of compound it is using data resources.
    - Structure can also be found using Mass or IR spectroscopy

    This is also useful to purify some liquids?
    I think I may have mixed HPLC with GC here

    Explain with reference to lattice & hydration enthalpies why hydroxides are more soluble as you go down group 2 & the opposite is the case for group 2.
    I thought whats the point of revision form the stuff u know
    GC- uses gas as mobile phase and liquid adsorbed on the surface of solid as stationary phase. gas passed under pressure and the rest is alright
    Its used for volatile compounds

    Increase in ionic radii so less attarction to OH. Lattice enthalpy decreases as the ionic radii goes on increasing hence less negative. Hydration enthalpy decreases as well as ionic radii increases down the group so again this is less negative.
    Since Hsolution = -Hlatt+ Hhydration H solution becomes lmore exo down the group so Stotal becomes more positive hence solubility increases.
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    (Original post by posthumus)
    Hehe, your evil... I told you that it's the one I need to go through!

    But tell me if I've missed out any points:
    - if Liquid is vaporized and carried by the mobile phase (which is an inert gas I think)
    - pushed through with pressure and through stationary phase
    - Stationary phase consists of solvent absorbed onto solid
    - The interaction between mobile & stationary phase determine how much time it takes for the mobile phase to go through, this is called the retention time.
    - Retention time is unique to specific compounds, look up what type of compound it is using data resources.
    - Structure can also be found using Mass or IR spectroscopy

    This is also useful to purify some liquids?
    I think I may have mixed HPLC with GC here

    Explain with reference to lattice & hydration enthalpies why hydroxides are more soluble as you go down group 2 & the opposite is the case for group 2.

    EDIT: opposite is the case for sulfates, sorry
    why is aldehyde more reactive than ketone?
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    (Original post by AS01)
    I thought whats the point of revision form the stuff u know
    GC- uses gas as mobile phase and liquid adsorbed on the surface of solid as stationary phase. gas passed under pressure and the rest is alright
    Its used for volatile compounds

    Increase in ionic radii so less attarction to OH. Lattice enthalpy decreases as the ionic radii goes on increasing hence less negative. Hydration enthalpy decreases as well as ionic radii increases down the group so again this is less negative.
    Since Hsolution = -Hlatt+ Hhydration H solution becomes lmore exo down the group so Stotal becomes more positive hence solubility increases.
    Aah good point ! I need lessons on how to revise

    Erm lattice enthalpy depends on sum of ionic radiis.... {r(+) + r(-)}
    The OH group has a very small radii therefore lattice enthalpy increases considerably as you go down since its negative lattice enthalpy... H solution becomes more exothermic favoring solubility as you go down

    However sulfate ions are much large {r(+) + r(-)} as cation radii increases as you go down the group the lattice enthalpy does not increase by a lot. This does not outweigh the hydration enthalpy so it's more endothermic as you go down. Hence solubility is less favored down group 2 sulfates.


    Is the C=O less polar in ketones due to alkyl groups pushing electrons towards the carbon and making it less delta positive. Therefore less likely to be attacked by nucelophile? Whereas aldehyde has a polar C=O bond.
    That's about all I have to say I don't know why aldehyde C=O is more polar though
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    (Original post by posthumus)
    Aah good point ! I need lessons on how to revise

    Erm lattice enthalpy depends on sum of ionic radiis.... {r(+) + r(-)}
    The OH group has a very small radii therefore lattice enthalpy increases considerably as you go down since its negative lattice enthalpy... H solution becomes more exothermic favoring solubility as you go down

    However sulfate ions are much large {r(+) + r(-)} as cation radii increases as you go down the group the lattice enthalpy does not increase by a lot. This does not outweigh the hydration enthalpy so it's more endothermic as you go down. Hence solubility is less favored down group 2 sulfates.


    Is the C=O less polar in ketones due to alkyl groups pushing electrons towards the carbon and making it less delta positive. Therefore less likely to be attacked by nucelophile? Whereas aldehyde has a polar C=O bond.
    That's about all I have to say I don't know why aldehyde C=O is more polar though
    um hydration enthalpy is always exo though
    yup! thats right and also aldehydes are less sterically hindered
    It is polar coz of difference in electronegativity
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    (Original post by AS01)
    um hydration enthalpy is always exo though
    yup! thats right and also aldehydes are less sterically hindered
    It is polar coz of difference in electronegativity
    Yh but hydration enthalpy decreases as you go down Think of it as the lattice enthalpy can't outweigh it, or keep up with the change (to outweight it) because it has a big anion {r(+) + r(-)}

    Okay now I see the flaw, it said this in george facer book.... is lattice enthalpy endothermic or exothermic ? (disregarding the negative sign) :confused:
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    (Original post by posthumus)
    Yh but hydration enthalpy decreases as you go down Think of it as the lattice enthalpy can't outweigh it, or keep up with the change (to outweight it) because it has a big anion {r(+) + r(-)}

    Okay now I see the flaw, it said this in george facer book.... is lattice enthalpy endothermic or exothermic ? (disregarding the negative sign) :confused:
    lol yeah! it becomes more positive for lattice enthalpy as it is -Hlatt so prolly the hydration enthalpy is more negative than lattice enthalpy
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    (Original post by AS01)
    lol yeah! it becomes more positive for lattice enthalpy as it is -Hlatt so prolly the hydration enthalpy is more negative than lattice enthalpy
    Ah yes, I see... Lattice enthalpy is less negative with the small OH- anion... therefore less positive -Hlatt ..... So therefore enthalpy of hydration is able to "keep up" and outweigh it!

    This whole time I thought lattice enthalpy was positive as energy is needed to break a lattice. But this probably goes back to the fact that all bond breaking is exothermic... which I don't think I ever will understand in my life
 
 
 
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