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    How do we know which ion goes to the electrode in electrolysis?

    Eg. the electrolysis of sodium chloride solution.
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    (Original post by zed963)
    How do we know which ion goes to the electrode in electrolysis?

    Eg. the electrolysis of sodium chloride solution.
    electrodes are of the cathode or anode. find out what they are in your books/notes

    also look up what electrolysis is and what it does - in terms of breaking a compound by chemical means.
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    (Original post by shengoc)
    electrodes are of the cathode or anode. find out what they are in your books/notes

    also look up what electrolysis is and what it does - in terms of breaking a compound by chemical means.
    AFAIK there are two electrodes which are in the electrolyte. The cathode is negative and attracts cations. The anode is positive and attracts anions.
    Electrolysis is the decomposition of a compound.

    What I'm asking is how do I know which ion discharges at the electrode.

    Eg. In sodium chloride solution we have Na+ H+ and OH- and Cl-

    So the cations go to the cathode and the anions go to the anode but which ion on the cathode or anode discharges first?
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    (Original post by zed963)
    AFAIK there are two electrodes which are in the electrolyte. The cathode is negative and attracts cations. The anode is positive and attracts anions.
    Electrolysis is the decomposition of a compound.

    What I'm asking is how do I know which ion discharges at the electrode.

    Eg. In sodium chloride solution we have Na+ H+ and OH- and Cl-

    So the cations go to the cathode and the anions go to the anode but which ion on the cathode or anode discharges first?
    There is an simple and a more complete answer to your question.

    The easy answer is that only metals less reactive than lead will be released at the cathode, otherwise it is hydrogen. Only halogens are released at the anode otherwise it's oxygen.

    If you require a more complete discussion ...
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    I have no idea what you're asking; what do you mean by 'discharges' first?
    Hydrogen is formed at the cathode, and chlorine is formed at the anode.
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    (Original post by Bude8)
    I have no idea what you're asking; what do you mean by 'discharges' first?
    Hydrogen is formed at the cathode, and chlorine is formed at the anode.
    Okay, so why isn't Na discharged or OH?
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    (Original post by charco)
    There is an simple and a more complete answer to your question.

    The easy answer is that only metals less reactive than lead will be released at the cathode, otherwise it is hydrogen. Only halogens are released at the anode otherwise it's oxygen.

    If you require a more complete discussion ...
    How will I know if the metal is less reactive than lead?
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    (Original post by zed963)
    Okay, so why isn't Na discharged or OH?
    Aqueous solutions contain four ions:
    A cation and an anion from the solute
    H+ and OH- from water

    At each electrode, only ONE ion can be discharged.
    The metal forms at the cathode ONLY IF it is below hydrogen in the reactivity series. If it's above hydrogen, then hydrogen itself is formed.

    At the anode the negative ion in the dissolved solid will be either mono atomic (eg Cl-, Br-, I-) or polyatomic (eg SO4 2-, NO3 -)
    If mono atomic, that is the ion that will be discharged.
    If polyatomic then hydroxide ions will be discharged, producing oxygen.
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    (Original post by zed963)
    How do we know which ion goes to the electrode in electrolysis?

    Eg. the electrolysis of sodium chloride solution.
    Are you having problems with the names of the electrodes, and which accepts which?
    I know it sounds silly, but this is the tactic I use to remember the electrodes:
    Cations are always positive. This is because, when you think of a cat ironing, it's probably happy. The Cation just moves towards the negative Cathode.
    Spoiler:
    Show
    The polarity of the cathode isn't actually always negative, but you don't really need to know that. You just need to know that Cations move towards the Cathode, and Anions move away from it.

    And once you know that cations are positive, you can infer that anions are negative.

    My high school Chemistry teacher used to use a misspelling of anode to explain that.
    the Annode is Not Negative, and therefore it is positive, so the negative anion moves toward it.

    I don't like that example, because you might put two n's in anion by accident. So yeah, i'm gonna advise the happy cat example.

    The above posts seem to explain pretty well which ions form where and why, so i'll leave that.
    Hope this helps!
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    (Original post by Bude8)
    Aqueous solutions contain four ions:
    A cation and an anion from the solute
    H+ and OH- from water

    At each electrode, only ONE ion can be discharged.
    The metal forms at the cathode ONLY IF it is below hydrogen in the reactivity series. If it's above hydrogen, then hydrogen itself is formed.

    At the anode the negative ion in the dissolved solid will be either mono atomic (eg Cl-, Br-, I-) or polyatomic (eg SO4 2-, NO3 -)
    If mono atomic, that is the ion that will be discharged.
    If polyatomic then hydroxide ions will be discharged, producing oxygen.
    What's the difference between mono atomic and polyatomic?
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    (Original post by zed963)
    What's the difference between mono atomic and polyatomic?
    mono = one
    poly = more than one (actually, many)
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    (Original post by charco)
    mono = one
    poly = more than one (actually, many)
    Will I have to memorise the reactivity series?
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    (Original post by zed963)
    What's the difference between mono atomic and polyatomic?
    Monoatomic are ions containing only one element. e.g Cl-

    Polyatomic are ions containing more than one element. e.g OH-
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    (Original post by zed963)
    Will I have to memorise the reactivity series?
    Depends on your syllabus, we do.
    Easy way to remember it:

    Please - Potassium
    Stop - Sodium
    Calling - Calcium
    My - Magnesium
    Annoying - Aluminium
    CARBON
    Zebra - Zinc
    In - Iron
    The - Tin
    Language - Lead
    HYDROGEN
    Class - Copper
    Silver
    Gold
    Platinum
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    (Original post by zed963)
    Will I have to memorise the reactivity series?
    If you're on AQA then no, It will be on the data sheet that is provided during the exam.
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    Is this site wrong http://alexteoh.com/emap-electrochem...Discharge.html

    It says that OH- is easier to discharge than Cl-
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    Trust me on this, have a look on GCSE bitesize at the video and revision notes. They're amazing
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    (Original post by Efemena15)
    Trust me on this, have a look on GCSE bitesize at the video and revision notes. They're amazing
    I find them to be basic.
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    (Original post by Bude8)
    Depends on your syllabus, we do.
    Easy way to remember it:

    Please - Potassium
    Stop - Sodium
    Calling - Calcium
    My - Magnesium
    Annoying - Aluminium
    CARBON
    Zebra - Zinc
    In - Iron
    The - Tin
    Language - Lead
    HYDROGEN
    Class - Copper
    Silver
    Gold
    Platinum
    Oh, Why's carbon is red for?

    Also, what's the half equation for OH-?
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    (Original post by zed963)
    Oh, Why's carbon is red for?

    Also, what's the half equation for OH-?
    There isn't a half equation for it because OH- doesn't react with the electrode, Cl- does.

    Half equation for Cl- would be 2Cl- - 2e-(electron) -> Cl2
 
 
 
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