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    (Original post by RoBiNBolt)
    Yoooo! Can anyone explain Bond Angles to me??
    Best way to put it is a central atom surrounded by:
    Example: CO, 2 atoms = 180 degrees, Shape: Linear
    Example: BF3, 3 atoms = 120 degrees, Shape: Trigonal Planar
    Example: CH4, 4 atoms = 109 degrees, Shape: Tetrahedral
    Example: PCl5, 5 atoms = 120 degrees and 90 degrees, Shape: Trigonal by-pyramidal
    Example: SF6, 6 atoms = 90 degrees, Shape: Octahedral (Counter-intuitive being SIX atoms...)

    Ammonia is a strange one, it has a lone pair so it is 109 degrees and is named as 'Pyramidal'
    Then finally an example of water which is 'Bent' or 'Boomerang' which has 2 lone pairs and so has a bond angle 109 degrees

    Hope that helps, its the best way I find to revise the shapes of molecules. Just remember that its all to do with the 'groups' of electrons NO MATTER how many electrons are in each group so if there are 3 groups made up of 2,2,4 electrons, then the bond angle is still 120 degrees as there are 3 groups of electrons!

    If anyone else needs help, I am happy to help if I know! Its good revision for me too!
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    Any chance of tomorrow's paper being leaked ?
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    (Original post by Garyglitter)
    Any chance of tomorrow's paper being leaked ?
    I highly doubt it. The papers are in our schools I think.
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    does anyone know how a zeolite works? i know it acts as a sieve to separate branched and unbranched isomers, but which does it allow to pass through? so confused!
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    (Original post by Janoskian)
    does anyone know how a zeolite works? i know it acts as a sieve to separate branched and unbranched isomers, but which does it allow to pass through? so confused!
    There's nothing about zeolites in the CI, just the CS book which i don't have.

    Gathered from mark schemes...it is a heterogeneous catalyst with a large surface area.
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    (Original post by Janoskian)
    does anyone know how a zeolite works? i know it acts as a sieve to separate branched and unbranched isomers, but which does it allow to pass through? so confused!
    Zeolite is shaped almost like a donut on a molecular level and so it has a hole through the middle that allows the straight chain isomers to pass through but restricts the passage of the short, branched isomers, thus separating the straight chains from the branched isomers
    Zeolite structure:
    http://www.co2crc.com.au/images/imag...tion_media.jpg
    See the hole through the middle?
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    A zeolite contains holes that trap the branched isomers and allows the unbranched (straight-chain) isomers to pass through.
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    (Original post by EstebanK0)
    There's nothing about zeolites in the CI, just the CS book which i don't have.

    Gathered from mark schemes...it is a heterogeneous catalyst with a large surface area.
    A zeolites are heterogeneous catalysts which have a large surface area, it also has pores which stop branched molecules from passing through.
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    (Original post by Ali_Ludley)
    Best way to put it is a central atom surrounded by:
    Example: CO, 2 atoms = 180 degrees, Shape: Linear
    Example: BF3, 3 atoms = 120 degrees, Shape: Trigonal Planar
    Example: CH4, 4 atoms = 109 degrees, Shape: Tetrahedral
    Example: PCl5, 5 atoms = 120 degrees and 90 degrees, Shape: Trigonal by-pyramidal
    Example: SF6, 6 atoms = 90 degrees, Shape: Octahedral (Counter-intuitive being SIX atoms...)

    Ammonia is a strange one, it has a lone pair so it is 109 degrees and is named as 'Pyramidal'
    Then finally an example of water which is 'Bent' or 'Boomerang' which has 2 lone pairs and so has a bond angle 109 degrees

    Hope that helps, its the best way I find to revise the shapes of molecules. Just remember that its all to do with the 'groups' of electrons NO MATTER how many electrons are in each group so if there are 3 groups made up of 2,2,4 electrons, then the bond angle is still 120 degrees as there are 3 groups of electrons!

    If anyone else needs help, I am happy to help if I know! Its good revision for me too!
    Hey how would you answer a 4 mark question on atomic emission spectra. All I know is E=hv. And if it says draw a diagram what would you draw?
    thanks
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    (Original post by EstebanK0)
    There's nothing about zeolites in the CI, just the CS book which i don't have.

    Gathered from mark schemes...it is a heterogeneous catalyst with a large surface area.
    Thanks!

    (Original post by Ali_Ludley)
    Zeolite is shaped almost like a donut on a molecular level and so it has a hole through the middle that allows the straight chain isomers to pass through but restricts the passage of the short, branched isomers, thus separating the straight chains from the branched isomers
    Zeolite structure:
    http://www.co2crc.com.au/images/imag...tion_media.jpg
    See the hole through the middle?
    haha thankyou!!

    (Original post by Sammydodga)
    A zeolite contains holes that trap the branched isomers and allows the unbranched (straight-chain) isomers to pass through.
    thanks!

    (Original post by momena)
    A zeolites are heterogeneous catalysts which have a large surface area, it also has pores which stop branched molecules from passing through.
    thanks!
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    (Original post by Sammydodga)
    Hey how would you answer a 4 mark question on atomic emission spectra. All I know is E=hv. And if it says draw a diagram what would you draw?
    thanks
    Tell us the full question(s).
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    (Original post by Sammydodga)
    Hey how would you answer a 4 mark question on atomic emission spectra. All I know is E=hv. And if it says draw a diagram what would you draw?
    thanks
    It solely depends upon what the question is asking but starting with what to draw.
    There are 2 drawings that could be drawn:
    1) The spectrum -
    The spectrum for an emission spectrum would be a black background with coloured lines on and it would have its lines converging at higher frequencies (energy). The lines signifying the electron's energy drop in this case (Delta E)
    2) The energy shells and electron movements -
    You would need to draw a set of energy shells that get closer together the farther up you go. In emission, the electrons in the atom are already in an 'excited' state so they drop down SPECIFIC energy levels all to one level (such as in the Lyman series which is all electrons drop to level 1). You would need to draw some arrows showing the drop in energy and then show that, that drop in energy represents a line on the spectra, the greater the delta E (Energy change), the higher up the line goes on the spectra (Lines converging at higher frequencies) and this ties in to E=hu.

    What I just wrote kind of also explains what to write given a 4 mark question but just remember these key points:
    - Atomic spectra is black lines, coloured background
    - Emission spectra is coloured lines, black background
    - Lines converge at higher frequencies
    - Electrons drop specific energy levels all to one shell (EMISSION) with the drop in energy being emitted as EM radiation in the form of light
    - OR (ABSORPTION) A atom is exposed to a spectrum of light and the electrons absorb a particular frequency of that light and raise up specific energy levels.
    - *Important* The lines on the spectra are constant for the same element so that is how we identify for example the composition of the outer layers of gasses of a star; Using an absorption spectrum, the opposite being the emission spectrum of a nebulae to see what elements make up the nebulae.

    Oh also remember that in a flame, electrons absorb the energy then emit it which is why you see a light in the flame.

    And I think that covers it all, hope it helps.
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    Can anyone talk me through this question?
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    (Original post by Kreayshawn)
    Can anyone talk me through this question?
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    First question:
    I think I have a rough idea. You can see the question already gives you the ratio which is 1:12.5 and now you need to figure out the moles of iso-octane with moles=mass/fm and from there you can figure out the dm^3 of oxygen required using Avagadro's law and then that answer equals 21% (Only oxygen volume and you need air) so find what 100% is. That should be your answer of air in dm^3. Try following those steps, I 'think' its right.

    Second question:
    Ga + As -> GaAs
    This gets you like 1 mark but its the state symbols that matter. It gives you the melting point of each element which are all above 298 kelvin which is 25 degrees Celsius (Standard conditions) so the elements will all be solid under standard conditions which enthalpy change of formation is under!
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    Wow thanks alot!

    Does anyone know how to calculate volumes?
    The question was Q3 in the January 2011 paper:
    Xe(g) + PtF6(g) = XePtF6

    Calculate the volume of xenon gas at room temperature and pressure that would be needed to produce 10g of XePtF6 on reaction with excess PtF6.
    One mole of gas at room temperature and pressure occupies 24dm3.
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    (Original post by Sammydodga)
    Wow thanks alot!

    Does anyone know how to calculate volumes?
    The question was Q3 in the January 2011 paper:
    Xe(g) + PtF6(g) = XePtF6

    Calculate the volume of xenon gas at room temperature and pressure that would be needed to produce 10g of XePtF6 on reaction with excess PtF6.
    One mole of gas at room temperature and pressure occupies 24dm3.
    Find moles of XePtF6
    moles = mass/fm = 10/(131+195+(19x6)) = 0.023

    Ratio is 1:1 mole ratio and this obeys Avagadro's law

    Times the moles (0.023) by 24 to get 0.54dm3 of Xenon (The answer here is in dm3)
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    (Original post by Ali_Ludley)
    Find moles of XePtF6
    moles = mass/fm = 10/(131+195+(19x6)) = 0.023

    Ratio is 1:1 mole ratio and this obeys Avagadro's law

    Times the moles (0.023) by 24 to get 0.54dm3 of Xenon (The answer here is in dm3)
    Thanks. You know for all questions that ask to calculate the volume of gas would you always work out the moles first and then just multiply it by 24 (the gas at room temp)?
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    (Original post by Sammydodga)
    Thanks. You know for all questions that ask to calculate the volume of gas would you always work out the moles first and then just multiply it by 24 (the gas at room temp)?
    Well yes when there is a solid involved, but when its gas to gas its just simply compare the ratios and then times through by 24dm3.
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    anybody know how to answer 3.a.i)
    http://www.ocr.org.uk/images/61538-q...y-for-life.pdf
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    (Original post by buzzing22)
    anybody know how to answer 3.a.i)
    http://www.ocr.org.uk/images/61538-q...y-for-life.pdf
    Its basically an estimation. As you can see the bond length increases down the group. Therefore any estimation between 0.23 and 0.30 would be correct really.
 
 
 
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