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Edexcel IAL Chemistry Unit 01 - 26th of May, 2017 Watch

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    Ok I couldn't find a thread for this exam so I decided to create one. We can discuss questions and share resources.
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    First of all, I was doing a past paper and I came up with a doubt.
    This is the question.
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    Why is the answer A instead of B. Why can't B be the answer?
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    group 1 nitrates only decompose to form metal nitrite and oxygen,
    except lithium which is also group 1 but lithium nitrate will decompose and form oxygen, metal oxide and nitrogen dioxide.
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    (Original post by tino083)
    group 1 nitrates only decompose to form metal nitrite and oxygen,
    except lithium which is also group 1 but lithium nitrate will decompose and form oxygen, metal oxide and nitrogen dioxide.
    thanks!
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    I have a doubt.
    What is the meaning of propagation reaction in organic chemistry?
    How do I write it when it's asked in the exam?

    Any help will be appreciated.
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    (Original post by Reshyna)
    I have a doubt.
    What is the meaning of propagation reaction in organic chemistry?
    How do I write it when it's asked in the exam?

    Any help will be appreciated.
    Propagation (I looked for the definition just incase you wanted a more formal explanation ) :
    Chain propagation (sometimes referred to as propagation) is a process in which a reactive intermediate is continuously regenerated during the course of a chemical chain reaction.

    So when writing the equations / formulas
    There will always be a free radical on both sides of it
    Use this link to look at examples
    Once you get it and practice it a little bit it will become very simple and is basically like free marks

    http://www.chemguide.co.uk/mechanism...ch4andcl2.html

    Best of luck
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    (Original post by LaylaM99)
    Propagation (I looked for the definition just incase you wanted a more formal explanation ) :
    Chain propagation (sometimes referred to as propagation) is a process in which a reactive intermediate is continuously regenerated during the course of a chemical chain reaction.

    So when writing the equations / formulas
    There will always be a free radical on both sides of it
    Use this link to look at examples
    Once you get it and practice it a little bit it will become very simple and is basically like free marks

    http://www.chemguide.co.uk/mechanism...ch4andcl2.html

    Best of luck
    Thank you so much Layla. So how was your chemistry exam? Was it easy? What did you get for the exam?
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    (Original post by Reshyna)
    Thank you so much Layla. So how was your chemistry exam? Was it easy? What did you get for the exam?
    It was a bit hard I couldn't focus.. the calculations got me confused and I don't know I'm just hoping for low grade boundaries

    Thanks for asking
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    (Original post by LaylaM99)
    It was a bit hard I couldn't focus.. the calculations got me confused and I don't know I'm just hoping for low grade boundaries

    Thanks for asking
    :console: don't worry.
    If the exams are tough, and if all students get like you know low marks the edexcel exam board will lower the grade boundaries. But if many students get marks get closer to the maximum, then the grade boundaries will be increased. You can see that in Edexcel-grading system ( an animated video that is easy to understand).

    So the most of the exam paper was calculations?

    It's okay. You've helped me so I asked you.
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    (Original post by Reshyna)
    :console: don't worry.
    If the exams are tough, and if all students get like you know low marks the edexcel exam board will lower the grade boundaries. But if many students get marks get closer to the maximum, then the grade boundaries will be increased. You can see that in Edexcel-grading system ( an animated video that is easy to understand).

    So the most of the exam paper was calculations?

    It's okay. You've helped me so I asked you.
    Yeah I know, hoping for the best
    No no it wasn't all calculations but the questions that had calculations were confusing
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    (Original post by LaylaM99)
    Yeah I know, hoping for the best
    No no it wasn't all calculations but the questions that had calculations were confusing
    Ah ok I understand.
    So what were the topics the paper covered?
    Theories? For example: Ionization energies, Bond enthalpies,...
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    If a carbon-carbon single bond is known as sigma bond, and a carbon-carbon double bond consists of a sigma bond and a pi bond, then what about carbon-carbon triple bond?
    What bonds does it contain?
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    (Original post by Reshyna)
    If a carbon-carbon single bond is known as sigma bond, and a carbon-carbon double bond consists of a sigma bond and a pi bond, then what about carbon-carbon triple bond?
    What bonds does it contain?
    Usually it is one pi bond and two sigma bonds. Generally in alkynes, sp hybrid orbitals (in the x axis) overlap to form a sigma bond, and p-orbitals in the y and z axes overlap to form a py-py pi bond and a pz-pz pi bond.
    The sigma bond is the strongest bond, and each pi bond is weaker than the next. Hence it is easy to break one pi bond (not much energy required), quite easy to break the second pi bond (a bit more energy), but more energy is then required to break the sigma bond. Hence they would break in that order.

    I'm not sure if you need to know about this for AS-level; OCR certainly don't expect knowledge of sp hybridisation at this level, I don't know about other boards.
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    (Original post by K-Man_PhysCheM)
    Usually it is one pi bond and two sigma bonds. Generally in alkynes, sp hybrid orbitals (in the x axis) overlap to form a sigma bond, and p-orbitals in the y and z axes overlap to form a py-py pi bond and a pz-pz pi bond.
    The sigma bond is the strongest bond, and each pi bond is weaker than the next. Hence it is easy to break one pi bond (not much energy required), quite easy to break the second pi bond (a bit more energy), but more energy is then required to break the sigma bond. Hence they would break in that order.

    I'm not sure if you need to know about this for AS-level; OCR certainly don't expect knowledge of sp hybridisation at this level, I don't know about other boards.
    Thanks a lot.
    My exam board is edexcel.
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    What do you mean by a 'singly positive ion'? :hmmmm:
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    (Original post by Reshyna)
    What do you mean by a 'singly positive ion'? :hmmmm:
    It's just an ion with one single positive charge, such as Na+.
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    (Original post by K-Man_PhysCheM)
    It's just an ion with one single positive charge, such as Na+.
    Thanks a lot
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    Could someone please explain me the difference between face-centred cubic struture and body-centred cubic structure?
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    Body-centred cubic is a unit cell structure with one atom in the middle of a 'cube' and 8 other atoms at the vertices of the cube. However, we say that the unit cell is made up of just 2 atoms because the 8 atoms on the vertices are each shared by eight unit cells in total, so a giant structure with 1,000,000,000,000 unit cells would only have (roughly) 2,000,000,000,000 atoms (though there would be some additional atoms around the outside surface that are in fewer than 8 unit cells, but at really large volumes this becomes negligible).

    Face-centred cubic unit cell has no atom in the centre, just eight atoms at the vertices of the cube and one atom on each face (there are 6 faces to a cube, so 6 atoms on faces). The atoms on each face are shared by two unit cells each, so really there are only 8*(1/8) + 6*(1/2) = 1 + 3 = 4 atoms per unit cell in a giant structure.
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    (Original post by K-Man_PhysCheM)
    Body-centred cubic is a unit cell structure with one atom in the middle of a 'cube' and 8 other atoms at the vertices of the cube. However, we say that the unit cell is made up of just 2 atoms because the 8 atoms on the vertices are each shared by eight unit cells in total, so a giant structure with 1,000,000,000,000 unit cells would only have (roughly) 2,000,000,000,000 atoms (though there would be some additional atoms around the outside surface that are in fewer than 8 unit cells, but at really large volumes this becomes negligible).

    Face-centred cubic unit cell has no atom in the centre, just eight atoms at the vertices of the cube and one atom on each face (there are 6 faces to a cube, so 6 atoms on faces). The atoms on each face are shared by two unit cells each, so really there are only 8*(1/8) + 6*(1/2) = 1 + 3 = 4 atoms per unit cell in a giant structure.
    Thanks for helping
    Now I'm clear with it
 
 
 
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