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    (Original post by samwillettsxxx)
    Thank you
    Anytime


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    hi can someone help me with this question thanks

    methanol starts to have toxic effects when it is present in blood at levels of above 200mg in 1000g
    express this in parts per million
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    (Original post by ilovecake123)
    hi can someone help me with this question thanks

    methanol starts to have toxic effects when it is present in blood at levels of above 200mg in 1000g
    express this in parts per million
    Convert 200mg to g
    Divide by 1000
    Times by 10^6

    Think how you would calculate percentage
    Same thing, just different number of zeros

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    (Original post by C0balt)
    Convert 200mg to g
    Divide by 1000
    Times by 10^6

    Think how you would calculate percentage
    Same thing, just different number of zeros

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    how do you convert into grams?
    thanks again
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    (Original post by ilovecake123)
    how do you convert into grams?
    thanks again
    x10^-3

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    aqa suck
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    When you're testing for halides, I know you would normally add nitric acid and then silver nitrate but what would be the reason for adding the silver nitrate first and then the nitric acid? Any help would be appreciated- just can't seem to think why you would do it that way!
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    (Original post by purplefoot)
    When you're testing for halides, I know you would normally add nitric acid and then silver nitrate but what would be the reason for adding the silver nitrate first and then the nitric acid? Any help would be appreciated- just can't seem to think why you would do it that way!
    Why shouldn't you? If you do it that way you can sort of use it as a test for carbonates

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    (Original post by samb1234)
    Why shouldn't you? If you do it that way you can sort of use it as a test for carbonates

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    Oh I see, thank you!
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    (Original post by purplefoot)
    Oh I see, thank you!
    They would never do it that way though so I don't think you would need to know why.
    The nitric acid is added first to make sure no ions interfere with the test with silver nitrate
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    (Original post by ilovecake123)
    hi can someone help me with this question thanks

    methanol starts to have toxic effects when it is present in blood at levels of above 200mg in 1000g
    express this in parts per million
    ppm= mass of solute (g) / mass of solution (g) x1000000

    so lets fill in the places

    milligrams means one thousandth of a gram so 200mg would be 0.2g because it's 200/1000

    in 1kg you have 1000g
    Now..
    ppm= 0.2/1000 X1000000
    = 200 ppm

    If you have any further questions let me know although someone called samb may be more suitable for help as I've forgotten half of AS chemistry lol
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    Question about redox here
    if the atom ox state goes up e.g +2 to +3 it's lost electrons and therefore has been oxidised
    and if the atom ox state goes down +1 to 0 then it's reduced - gained electrons????

    i just can't get my head round it
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    (Original post by samwillettsxxx)
    Question about redox here
    if the atom ox state goes up e.g +2 to +3 it's lost electrons and therefore has been oxidised
    and if the atom ox state goes down +1 to 0 then it's reduced - gained electrons????

    i just can't get my head round it
    Remember this mnemonic.

    OIL RIG

    Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).

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    (Original post by James A)
    Remember this mnemonic.

    OIL RIG

    Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).

    Yes thank you I use that but I mean is the going up going down of numbers I wrote right?
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    (Original post by samwillettsxxx)
    Question about redox here
    if the atom ox state goes up e.g +2 to +3 it's lost electrons and therefore has been oxidised
    and if the atom ox state goes down +1 to 0 then it's reduced - gained electrons????

    i just can't get my head round it
    Posted from TSR Mobile

    You're right. When an atom/compound/molecule loses electrons, it is oxidised. E.g +1 -----> +2. That would mean 1 electron was lost by the atom/compound/molecule

    When an atom/compound/molecule gains electrons, It is reduced. E.g 0 -----------> -3. That would mean that the atom/compound/molecule gained 3 electrons.
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    (Original post by samwillettsxxx)
    Yes thank you I use that but I mean is the going up going down of numbers I wrote right?
    Yeah it is.

    Just remember that an electron carries a negative charge (-1), so if you remove an electron (oxidation) then the number will increase on the atom that you are looking at.


    e.g:

    Fe(2+) -----------> Fe(3+) + e-
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    (Original post by _NMcC_)
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    You're right. When an atom/compound/molecule loses electrons, it is oxidised. E.g +1 -----> +2. That would mean 1 electron was lost by the atom/compound/molecule

    When an atom/compound/molecule gains electrons, It is reduced. E.g 0 -----------> -3. That would mean that the atom/compound/molecule gained 3 electrons.
    Thank you
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    Who has already done their empa?


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    Could someone help me with this question please? Thank you :hmmm:

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    (Original post by TeaAndTextbooks)
    Could someone help me with this question please? Thank you :hmmm:

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    290. 10% reacts so because of the fact the mole ratios that 30cm3 becomes 20cm3 and you have 270 that never reacted

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