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    Hi I'm doing OCR A Chemistry. How is everyone feeling for the F322 paper?
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    (Original post by Dinaa)
    Help with redox ewuation for SO4 2- ---> SO2
    Does it mention whether it's in acidic medium or alkaline medium?

    In acidic medium:

    SO42- + 4H+ + 2e- ------> SO2 + 2H2O
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    How do you tell if a molecule is polar or not?
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    (Original post by C0balt)
    :five: Cobalt was taken lol
    now I know how to spell phenolphthalein thanks to your name
    I did actually see a mark scheme that specifically said to reject phenolphthalein if you spelt it wrong lol

    Posted from TSR Mobile
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    (Original post by samb1234)
    I did actually see a mark scheme that specifically said to reject phenolphthalein if you spelt it wrong lol

    Posted from TSR Mobile
    yeah usually they accept recognisable phonetic spelling but once they felt like rejecting lol
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    guys, any tips on working these kinds of questions out? I usually always lose the marks for these and i don't think it's mentioned in the OCR book.
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    (Original post by leilaspicer97)
    How do you tell if a molecule is polar or not?
    If you mean by experimentation, you can place the liquid to be tested in a burette and allow a narrow stream to run out. Then you can place a charged rod next to the flow and it should slightly change direction towards the rod if it's polar due to the attraction.

    If you mean in general:

    Polarity has a magnitude and direction, so for a molecule to be polar there has to be a 'net dipole moment'. This means that the dipoles in a molecule do not cancel each other out.

    Non-polar molecules have dipoles that cancel out each other.
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    (Original post by leilaspicer97)
    How do you tell if a molecule is polar or not?
    First, check if there are atoms with different electronegativities bonded together. (Like C-Cl, O-H) These are polar bonds.
    Next, see if the molecule is symmetrical. Do the polar bonds cancel out? If they don't, then you have a polar molecule!
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    (Original post by TeachChemistry)
    See below.
    That makes so much sense! thankyou
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    (Original post by TheNoobishKnight)
    guys, any tips on working these kinds of questions out? I usually always lose the marks for these and i don't think it's mentioned in the OCR book.
    i) I'm assuming you know how to draw the graph?

    ii) The definition for enthalpy change of formation states it's the enthalpy change when forming one mole. The equation above shows the formation of two moles, so you have to divide the enthalpy change by two.

    iii) For this one it has to be lower than 250kJmol^-1

    iv) So for the reverse reaction, you would have follow the graph in the opposite direction, from right to left. So you go up 92kJmol^-1 from the products to the reactants, and then up to the activation energy. Then up the activation energy of 250kJmol^-1 to get a total of 342kJmol^-1, (92 + 250) .
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    This comes up in the OCR B Salters spec, anyone know what it means / how you would answer it??? Its talking about electrophilic addition mechanism


    "explain how the products obtained when other anions are present confirm the model of the mechanism"
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    Could someone explain this to me.. Halides are reducing agents and halogens are oxidising agents. okay
    Now when It comes to iodine-sodium thiosulfate titration, why is Iodide ions considered to be an oxidizing agent.
    I understand that  2I^- I2+ 2e but aren't halides suppose to be reducing agents only??
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    (Original post by thymolphthalein)
    If you mean by experimentation, you can place the liquid to be tested in a burette and allow a narrow stream to run out. Then you can place a charged rod next to the flow and it should slightly change direction towards the rod if it's polar due to the attraction.

    If you mean in general:

    Polarity has a magnitude and direction, so for a molecule to be polar there has to be a 'net dipole moment'. This means that the dipoles in a molecule do not cancel each other out.

    Non-polar molecules have dipoles that cancel out each other.
    Yeah I meant generally, thank you how can they cancel out?
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    (Original post by kawehi)
    First, check if there are atoms with different electronegativities bonded together. (Like C-Cl, O-H) These are polar bonds.
    Next, see if the molecule is symmetrical. Do the polar bonds cancel out? If they don't, then you have a polar molecule!
    Thank you it's they cancelling out part that I don't really get :/
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    (Original post by leilaspicer97)
    Thank you it's they cancelling out part that I don't really get :/
    Ok, I'll try to give you some examples!

    SF6

    So, Fluorine has a higher electronegativity than Sulfur, right? So the electron density is more attracted to the F atoms than the S atoms. This gives F a negative dipole. However, overall SF6 isn't polar! This is because, for every negative dipole on one side of the molecule, there's another, equal negative dipole on the other side. You can imagine it sort of like a tug of war, if there are 2 people of equal strength on both sides, then everything is cancelled out, and the rope doesn't move. To get the mark in the exam, say that the molecule is symmetrical, so the charges balance. (2 marks)

    HCl

    Cl has a higher electronegativity than H, which means that the electron density is more attracted to the Cl. You can see in the image above, most of the electron density is surrounding the Cl atom. Overall, HCl is polar! This is because the H-Cl bond is polar (Cl has the negative dipole), AND there isn't another, equal negative dipole on the other side of the hydrogen! Therefore, the charges to NOT cancel out, and there is an overall dipole, due to the asymmetrical nature of the molecule.

    Hope this helps!
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    HELP PLEASE!!!
    describe type of radiation involved in the greenhouse effect and how the GHE warms up the atmosphere....(7)
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    (Original post by kawehi)
    Ok, I'll try to give you some examples!

    SF6

    So, Fluorine has a higher electronegativity than Sulfur, right? So the electron density is more attracted to the F atoms than the S atoms. This gives F a negative dipole. However, overall SF6 isn't polar! This is because, for every negative dipole on one side of the molecule, there's another, equal negative dipole on the other side. You can imagine it sort of like a tug of war, if there are 2 people of equal strength on both sides, then everything is cancelled out, and the rope doesn't move. To get the mark in the exam, say that the molecule is symmetrical, so the charges balance. (2 marks)

    HCl

    Cl has a higher electronegativity than H, which means that the electron density is more attracted to the Cl. You can see in the image above, most of the electron density is surrounding the Cl atom. Overall, HCl is polar! This is because the H-Cl bond is polar (Cl has the negative dipole), AND there isn't another, equal negative dipole on the other side of the hydrogen! Therefore, the charges to NOT cancel out, and there is an overall dipole, due to the asymmetrical nature of the molecule.

    Hope this helps!
    Thank you!!!!!!thats was so much easier to understand
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    (Original post by mismash)
    HELP PLEASE!!!
    describe type of radiation involved in the greenhouse effect and how the GHE warms up the atmosphere....(7)
    Is this an actual past paper Q? Which exam board/year?
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    (Original post by mismash)
    HELP PLEASE!!!
    describe type of radiation involved in the greenhouse effect and how the GHE warms up the atmosphere....(7)
    7 marks?:eek:

    I'm still awake for some reason, so I'll try answering this.

    When sunlight hits the earth, some of it is re-emitted back as infra red radiation.

    Only gases with polar bonds such as water vapour or carbon oxide can absorb this infra-red radiation.To achieve this, the molecule changes its own dipole moment during the vibration/bending of bonds in the molecule.

    These gases in the air re-emit the absorbed radiation, causing the atmosphere of the Earth to heat up. This effect is known as the green house effect and the gases responsible for this are known as green house gases.

    The increased concentration of known greenhouse gases and the introduction of new greenhouse gases due to human activity has led to a much greater amount of radiation being trapped causing an increase in the temperature of the Earth's atmosphere. This increase in air temperature is known as global warming.

    I tried.
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    Please anyone answer me, what does INTERMEDIATE mean in intermediate bonding and also homogeneous catalysts work by forming intermediates ??:confused:
 
 
 
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