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UNOFFICIAL MARK SCHEME - AQA AS Chemistry 13/01/2012 (UPDATED)

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    Unofficial Mark Scheme – AS AQA Chemistry 13/01/12
    This is a prediction I have adapted and changed, so don't panic if your questions vary and questions are not in right order but I ensure you the marks are all there, if not this is all from memory remember, play nice and enjoy
    [*] - Indicated my side comments

    1) State this bond & How it is formed;
    Covalent bond (1 mark) Shared pair of electrons *between non-metal atoms (1 mark)

    2) Shapes of Molecules questions;
    - BF3 (should resemble a trigonal planar shape OR t-shaped (since a previous mark scheme allows both), incorporated with two lone pairs) (1 mark)
    - Angle *There is debate with this so these are what most people have said
    - 120 (115-120) OR 90 (85-90) (1 mark)

    - BrF4 (Should resemble Square Planar Shape, incorporated with two lone pairs) (1 mark)
    - Angle: 90 (1 mark)

    3) Why does KbrF4 have a higher melting point?, explain in terms of bonding.
    *Therefore including structure wouldn’t gain/loose any marks if added
    - Ionic bonding (1 mark) electrostatic forces/attraction between K+ and Br- oppositely charged ions (1 marks) require a lot of energy to overcome (1 mark)

    4) Volume question, to be converted from cm3 to m3 s
    PV = nRT or V = nRT/P (1 mark)
    Correctly changing 101kpa to 101,000 pa & cm3 to m3 by x by (10 to the power of -6) (1 mark)
    Answer is 0.0260 (1 marks)
    *If you got 0.0175, or something like that it is because you forgot to convert cm3 tom3 or didnt convert it properly but all is not lost, since you get marks for working out


    . Calculation questions for Volume of Nitric acid = 0.0524 dm3

    *my working out:
    8.14 / 207.2 = 0.0393
    Then to get moles of n02 you times by 8/3 (due to 3:8 ratio)
    so 0.0393 x 8/3 = 0.1048 moles of n02
    ( 2 marks - for correct working out)

    then 0.1048/ 2.00 (conc) to get volumes = 0.0524 dm3 (1 mark for correct answer and unit)

    5) Which element in group 2, has the largest atomic radius?
    - Lithium (1 mark)
    *I assure you, they did not ask why or why there was a trend, ignore any unofficial mark scheme which say so.

    6) How would HCL be labelled?
    Irritant/Corrosive/Toxic (1 mark)

    7) Electron Configuration; 1s2 2s2 2p6
    . (N) 3- (1 mark)
    . (F) - (1 mark)

    *I also included the proton number/atomic number, if you also did so I highly doubt they will penalise marks for addition information, as long as it does not contradict.

    . Why does Fluorine have a low melting Point?
    Simple Molecular ( 1 mark)
    Weak van de Waals forces between molecules ( 1 mark)


    8).Name/State Formulae for Lithium Nitride
    Li3N (1 mark)

    . Calcium Nitride Empirical Formulae
    Correctly stating percentage of Nitrogen (1 mark)
    Correct method used ( 1 mark)
    Ca3n2 (1 mark)

    9) Balance Equation for Lead Nitrate
    2___ + 2___ -----> 4___ + 1___
    * You did not need to include 1 in front of the 02 at the end as this goes without saying.

    10) Sulphur Compounds impact on Environment?
    - (Contributed to) Acid Rain (1 mark)

    11) Equation to show how CO & NO is removed in a Catalytic Converter
    2NO + 2CO -> N2 + 2CO2 ( 1 mark)

    12) Equation to show how Si3N4 is formed (1 mark)

    3Si + 2N2 -> 3SiN4
    OR
    1/5 Si2+ N4 --> Si3N4
    *There is debate in this however multiples are definitely allowed.


    13) Atom Economy Question
    Correct method (2 marks)
    Correct Answer 76.4% (1 mark)
    * Cant remember to what decimal place but it 76.??

    14) Why does Carbon have a high melting point?
    Macromolecular (1 mark)
    Each carbon is covalently bonded to four other carbons (making a tetrahedral shake), networking throughout structure (1 mark)
    Strong Covalent bonds ( 1 mark)
    Alot of energy is required to overcome/break bonds (1 mark)

    15) Completing Graph for Nitrogen
    Nitrogen should be plotted with an X, lower than all other elements but NOT on 0.
    ( 1 mark)

    16) What raw material is Hexane Obtained from?
    Crude Oil ( 1 mark)

    17)
    . What substance/material would be used to remove Sulphur
    CaO (Calcium Oxide) or CaCO3 (Limstone) ( 1 mark)
    . Why is this used?
    If you used CaO - It neutralised acid in Sulphur impurity (there is debate for this, I didnt personally use Ca0 so cannot give judgement) (1 mark)
    . If used CaCO3 - Limestone can be easily accessed/high in abundance/ there is high supply (1 mark)

    18) Draw how H-F molecules interact..
    Partial Charges correctly indicated (1 mark)
    3 Lone pairs of Fluoride ( 1 mark)
    Hydrogen Bond (- - - -) Between Delta Plus H and Fluoride lone pair of a different molecules ( 1 mark)

    19) Which type of Cracking produces high % of Alkenes?
    - Thermal Cracking ( 1 mark)
    State conditions required
    - High Temperate and Pressure ( 1 mark)
    *You could also gain these marks if you said the actual temperature and pressure required

    20) State why Zeolite/Catalyst is used in Catalytic converters
    - (Extremely) Large surface area for reaction to take place (1 mark)

    21) How many isomers does Hexane have
    5 (1 mark)

    22) Name the Compound shown
    2,2-dichloro-3-methlypentane

    .Type of Isomer shown?
    Chain Isomerism/Isomer ( 1 mark)

    23) Empirical forum ale for compound
    C3H6CL (1 mark)

    24) How is Krypton Ionised
    Electron Gun (1 mark)
    bombards/hits Krpton Sample ( 1 mark)
    Knocking off electrons forming possitive ions/1+ ions/2+ions ( 1 marks)

    25) Ar of Krpton
    For correct method (2 marks)
    Correct answer to one decimal place 84.0 (1 mark)

    . Give reasons why your Ar is different to that of the periodic table (1 mark)
    *Again there is debate; so these are the 2 most logical answers people gave
    - Mass Spectrometer used for Ar in Periodic table was of a higher resolution than that given in the table therefore answer is more precise/accurate
    OR
    - Fragments may of fallen off before ions reached detector

    (The reason I havent included the meteorite answers because Krpton is the same whatever planet, adding meteorite was just a way of applying knowledge to real-life situations it didn't play any real part in the question for example "Sanjeev and Alice did an experiment" you wouldnt say Sanjeev is more reliable simple because he a boy?, the fact the krpton was apart of the meteorite was a decoy it played no part.)

    26) Equation for 1st IE of Krypton.

    Kr(g) + e- -> Kr+(g) + 2e-

    Or

    Kr(g) -> Kr+(g) + e-

    For correct state symbols (1 mark)
    for Correct equation (1 mark)

    27) Explain peak at 42
    - (When Krpton sample ionised) a 2+ ion charge/double charged ion was created ( 1 mark)

    -

    27) Which element deviates from Period 2, general trend, from Li to N
    Boron (1 mark)
    *If you said Oxygen this would be wrong since they've given you a boundary of from Lithium to Nitrogen

    .Explain why
    Outer electron is 2p Orbital, Higher energy level than Be in 2s ( 1 mark)
    More shielding (as more inner main energy shells) (1 mark)

    28) Processed used to obtain Hexane from Crude Oil
    Fractional Distillation ( 1 mark)

    29) Why it is not possible to get pure N0 on its own? (1 mark)
    *There is debate with this answer; I have been suggested the most and make the most logical sense

    - NO reacts with water (vapour) in air to form H2N03 (Nitric Acid)
    OR
    - NO reacts with air to form Nitrogen Dioxide?
    OR
    - NO was not only gaseous product so may of reacted with 02 to form N03 which may be hard to seperate?
    *predictions here people
    (- The reason why 'N0 escpaing into air' wont be accepted is because, you havent explained how that makes it impure? If the question was why can N0 not be 100% obtained/collected which is the next question then that answer would would but its talking about purity.)

    . Why is it not possible to get 100% yield of N0 (1 mark)
    - Not high enough Temperature/Pressure for Lead Nitrate to completely decompose
    OR
    - N0 make escape into air, due to being a gas

    There was also an equation for write equation for incomplete/complete combustion of an Octane
    (cant remember)
    but this was (1 mark)
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    Thanks for this Just realised I got less than a U.
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    (Original post by king101)
    Thanks for this Just realised I got less than a U.
    Being Negative wont help.,
    I doubt you got a U, just keep your head up high.
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    Cheers for this man, I'm quite confident, but it was quite a hard exam compared to June last year.

    Hopefully the grade boundaries will be nice and low!
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    Does this really need a negative rating....

    Does my exam board really need your re-evaluation?
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    people still say 'woops' i'm an advocate of this..
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    Not sure if I've lost the ability to add after maths this morning but I'm sure these marks don't add up close to 70. Are questions missing?
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    No, well not a U..But I really put a lot of revision into it and really messed up, and make bad mistakes such as deviation i.e. put down oxygen instead of Boron >
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    (Original post by Folks)
    Not sure if I've lost the ability to add after maths this morning but I'm sure these marks don't add up close to 70. Are questions missing?

    Which is why I've clearly stated at the buttom, 'Anymore questions?'
    I don't see you contributing or producing a mark scheme so play nice.
    :giggle:
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    (Original post by PowerPuff)
    UNOFFICIAL MARK SCHEME - AQA AS Chemistry 13/01/2011 -
    This Mark Scheme is an Unofficial Mark Scheme (simply predictions)
    * indicates my side comments.
    Some questions are missing, so feel free to add any.

    1)State the type of bond and explain how it is formed:
    Covalent, shared pair of electrons. (2marks; 1 for covalent, 1 for shared pair)

    Q) 2 Shape of BrF3

    (Resembles trigonal bypyramidal) angle between BONDING pairs, 90 degrees, ( 85-90 ) ( 2 marks, 1 for shape, one for angle)

    Square planar, 120degrees ( 85-90 ) ( 2 marks; 1 for shape, one for angle )

    3 High melting point of KBrF4-... ??

    Giant ionic structure. Strong oppositely charged ions keep structure together, lots of energy required to overcome these forces. (3 marks; 1 for giant ionic structure, 1 for strong forces of opp charged ions, 1 for overcoming forces )
    *Myself and others believe that if you said just Ionic bonding instead of Gian Ionic strcuture, you can still get 3 marks since the question asked 'in terms of bonding' so stating the structure wouldnt be needed.

    Q) PV= nRT question

    0.0175 ( 4marks)

    Q) Which element has smallest atomic radii ?

    Lithium ( 1 mark )

    Q) how does atomic radii change across a period in period 2
    Decreases
    *many people are saying they asked why, but I assure you they did not

    Q) Label for HCl.
    corrosive, toxic, irritant (1 mark)

    Q) Nitride ion with same electronic configuration as 1s2 2s2 2p6?

    N 3- ion ( 1mark )

    Q) Element Q

    F- ion ( 1 mark )

    Q) question that follows after F- ion question; Li3N ??? (1 mark)

    Q) empirical formula of Calcium nitride.

    Ca3N2 (3 mark; 2 for appropriate method, 1 for answer)

    Q) Balancing lead nitrate equation

    2 2 4 1 ( 1 mark ) ( multiples are accepted )
    [COLOR="rgb(75, 0, 130)"]*myself and others believe that you can still get full mark if you didnt state a 1 infront of the 02, since it goes without saying[/COLOR]
    Q) Environmental dangers of Sulfur compounds

    Acid rain ( 1 mark )

    Q)Equation of removal of CO or NO ? ( cant remmeber which it was )

    2NO + 2CO -> N2 + 2CO2 (1 mark)

    Q) Si equation of some sort to form Si3N4

    3Si + 2N2 -> 3SiN4 (1 mark )

    Q) Calculation questions for Volume of Nitric acid = 0.0524 dm3
    (3marks)
    [COLOR="rgb(72, 61, 139)"]*my working out:
    8.14 / 207.2 = 0.0393
    Then to get moles of n02 you times by 8/3 (due to 3:8 ratio)
    so 0.0393 x 8/3 = 0.1048 moles of n02

    then 0.1048/ 2.00 (conc) to get volumes = 0.0524 dm3[/COLOR]


    157/207 x 100 = 76ish % atom economy ? (3marks)

    Q) High melting point of Carbon,

    Readily forms strong covalent bonds with 4 other carbon atoms, forming giant covalent structure. These strong covalent bonds spread throughout the structure and they MUST be broken. Require a lot of energy to break these strong forces. ( 3 marks; 1 mark for readily forms bonds with 4 other C atoms, 1 for giant covalent structure or macromolecular, 1 for strong bonds must be broken, 1 for require a lot of energy to break )
    [COLOR="rgb(75, 0, 130)"]*I also mentioned tetrahedral like structure[/COLOR]

    Q) Cross for nitrogen

    Nitrogen in the graph should appear lower than all other elements plotted (1 mark)

    Q) which raw material is hexane obtained from ?

    Crude oil (1 mark )

    Q) How to remove sulfur ?

    React with CaO, neutralises sulfur. ( 2 marks )
    *However some mentioned CaC03 (limestone) and reason because it is easily accesible/high in abundance/can be easily collected

    Q) Bonding between two molecules of H-F

    F has delta +, H has delta -, F has 3 lone pairs, H atom of another H-F molecule bonded to a lone pair from F atom in other molecule. ( 2 marks ? )

    Q) which cracking method produces high % of alkenes and state conditions

    Thermal cracking, high temp and pressure ( 2 marks; 1 for thermal cracking, 1 for both conditions )

    Q) State a catalyst used in exausht pipes to remove NO and CO and explain the benefit of having honey comb structure ??

    Rh/Pt/Pl , Increased surface area for reaction. ( 2 marks )

    Q) Number of isomers ?

    5 ( 1 mark )

    Q) name of compound shown ?

    2,2-dichloro,3-methylpentane ( 1mark )

    Q) empirical formula of compound shown ?

    C3H6Cl ( 1mark )

    Q) how is Kr ionised ?
    Krypton is ionised by electron gun that fires electron at high speed at gaseous sample of Kr atom knocking an e- out by repulsion. (3marks)

    Q) Ar of Kr in sample = 84.0 (4marks)
    *needed a .0 as question stated in one decimal place.

    Q) why is the value of Ar you obtained different from periodic table ?
    Argument for this,

    One view: Something about space, so different values
    Second view: (which I put) Mass spectrometer used for periodic table may be of high resolution so more precise/accurate
    Third view: something about different isotopes


    Q) IE change for 1st IE of Krypton.

    Kr(g) + e- -> Kr+(g) + e-

    Or

    Kr(g) -> Kr+(g) + e- (2marks; 1 for states, 1 for correct equation)

    Q) which element deviates from general trend of first IE in period 2 ?. Explain why.

    Boron, electron in 2p orbital, Beryllium has electron in 2s orbital. 2p is of slightly higher energy than 2s orbital, less shielding, less energy required to remove. ( 3marks )

    Q) Explain peak at 42,

    I said: Krpton may of been ionisied to form 2+ charge which is rare/occurs less likely so abundance is smaller and also M/Z is smaller/ behaves as a ion half its mass
    (2marks)




    Anymore people?
    I reckon it would've been a good idea to say i created this :P ...
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    (Original post by iAre Teh Lejend)
    I reckon it would've been a good idea to say i created this :P ...
    You created the exam paper?
    I think not, also I tweeked some of the answers since, you claimed they asked WHY the atomic raidus trend decreased, which they didnt.

    I also included alternative answers, since yours was slightly subjective
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    isn't square planar 90 and trigonal bipyramidal 120? i somehow got 120 degrees even though I misread the chemical, thought it was bf3 and did trigonal planar, god damn I really cannot be bothered resitting this -___________________-

    I estimated 49/70.. really wanted an A man.. thanks for the post though!
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    (Original post by PowerPuff)
    You created the exam paper?
    I think not, also I tweeked some of the answers since, you claimed they asked WHY the atomic raidus trend decreased, which they didnt.

    I also included alternative answers, since yours was slightly subjective
    No I created the markscheme dude... and who cares whether they asked why or how,same thing dude people doing a-level chem should have brains to work that out,mehhhhh
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    (Original post by iAre Teh Lejend)
    No I created the markscheme dude... and who cares whether they asked why or how,same thing dude people doing a-level chem should have brains to work that out,mehhhhh
    That didnt make sense,
    They didnt ask anything to do with why/how their was a trend for atomic size,
    it simple asked which element had the larget atomic size, and moved on.
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    The first ionisation energy trend qu- Carbon

    The question where you had to draw the hydrogen bonding between HF was 3 marks I think.
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    (Original post by PowerPuff)
    Which is why I've clearly stated at the buttom, 'Anymore questions?'
    I don't see you contributing or producing a mark scheme so play nice.
    :giggle:
    I didn't think I implied any sort of negative tone
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    (Original post by Member737,514)
    The first ionisation energy trend qu- Carbon

    The question where you had to draw the hydrogen bonding between HF was 3 marks I think.
    WOOHOO

    man if 50 is an A and i get 50 im gonna be HAPPY, hope the same goes for physics
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    What grade would be 38-42?
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    (Original post by PowerPuff)
    That didnt make sense,
    They didnt ask anything to do with why/how their was a trend for atomic size,
    it simple asked which element had the larget atomic size, and moved on.
    Agreed, and also they're not the same thing. Once wants an explanation one wants to know which element.

    There was also one, just after the crude oil question, regarding what the process is called with the answer been Fractional Distillation.

    Also, even if he did use most of your mark scheme, he's made it more accessible to people.

    I made some silly mistakes, I'll be happy with a B I might JUST scrape an A if the boundaries are low.
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    (Original post by PowerPuff)
    That didnt make sense,
    They didnt ask anything to do with why/how their was a trend for atomic size,
    it simple asked which element had the larget atomic size, and moved on.

    (Original post by iAre Teh Lejend)
    No I created the markscheme dude... and who cares whether they asked why or how,same thing dude people doing a-level chem should have brains to work that out,mehhhhh
    I think iAre Teh Lejend should get credit for actually producing the mark scheme and Powerpuff can get credit for editing. It's only fair that way since he did actually make it first.

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