Electrolysis

00:32:45
https://www.youtube.com/watch?v=dRtSjJCKkIo

摘要

TLDRAz elektrolízis egy olyan kémiai technika, amely elektromos energiát használ nem spontán kémiai reakciók kiváltására. Az elektrolízis segítségével kémiai vegyületeket lehet összetevőikre bontani. Ahhoz, hogy a nátrium-klorid (konyhasó) nátriumfémre és klórgázra bomoljon, elektromos áram szükséges, mivel a reakció nem megy végbe magától, idézve a videó egy példáját. Az elektrolízis során nátrium kerül redukcióra, míg a klorid ionok oxidációra kerülnek. Hasonlóképpen a víz elektrolízisével hidrogén és oxigéngáz is előállítható. Mivel ezek az eljárások nagy mennyiségű energiát igényelnek, különféle berendezéseket, mint például elektrolytcella, alkalmaznak a folyamat megkönnyítésére.

心得

  • ⚡ Elektrolízis elektromos áramot használ kémiai reakciók létrehozására.
  • 🔋 A nátrium-klorid elektromos bontása nátriumfémre és klórgázra történik.
  • 💡 Az oxidáció és redukció folyamatai az elektrolízis központi részei.
  • 🔥 A víz elektrolíziséhez szükséges elektrolyt használata segíti az áramvezetést.
  • 🌡️ Az elektrolízis folyamata magas hőmérsékletet igényel olvadékok esetében.
  • 🔍 Az elektrolízis reakciók egyesíthetők félreakciókból.
  • 🔌 Az elektrolizáló cellák speciális berendezések a folyamat végrehajtásához.
  • 🚫 Ezek a kémiai reakciók nem önállóan spontának.
  • 📑 Az elektrolízis folyamata több lépésből és részletből áll.
  • ⚗️ Vegyületek bontása során a gázok elvezethetők, hogy tárolhatók legyenek.

时间轴

  • 00:00:00 - 00:05:00

    Az elektrolízis egy folyamat, amelyben az elektromosság kémiai változást idéz elő, amely másképp nem történne meg. Az elektrolízist gyakran használják vegyületek elemeikre történő bontására. Első példánk a nátrium-klorid elektrolízissel történő bontása nátriumfémre és klórgázra, bár az egyenlet nincs kiegyensúlyozva. A nátrium-klorid esetében ez egy oxidáció-redukciós reakció, ahol az elektronok mozognak az atomok között. A nátrium redukálódik, míg a klorid oxidálódik, elektronokat veszítve. Ezt a folyamatot nem spontán módon történik, ezért elektromos energiára van szükség az elektrolízishez.

  • 00:05:00 - 00:10:00

    Az elemzés szerint a nátrium-klorid nem bomlik le spontán módon nátriumra és klórgázra, mivel a vegyület elemei elégedettek az elektronjaik számával. Az elektrolízishez szükséges elektromos energia forrása az akkumulátor, amely az elektronokat mozgatja az elektródák között. Az anód oxidáció, a katód redukció helyszíne; az elektronok mozgásának követése segít megérteni a folyamatot. Az olvadt nátrium-klorid magas hőmérsékleten képes elektrolízisre, ahol a nátrium-ionok elektronokat kapnak, míg a klorid-ionok elveszítik azokat, a klór pedig diatomikus molekulát képez.

  • 00:10:00 - 00:15:00

    Az elektrolízis folyamatának demonstrálásához használt eszköz egy elektrolitikus cella, ahol a katódon lévő negatív töltésű nátrium-ionok redukálódnak, míg az anódon lévő klorid-ionokat oxidálódnak. Az elektrokémiai reakciók során az elektromosság az alapkomponenseket (nátrium és klór) szétválasztja, elősegítve a nátrium és a klórgáz termelését. A folyamat nem spontán, az elektródák közötti elektron mozgása kritikus az eredmény eléréséhez, szemléltetve ezzel az oxidáció és redukció dinamikáját elektrokémiai környezetben.

  • 00:15:00 - 00:20:00

    A víz elektrolízise során az áram segítségével a víz molekuláit hidrogén- és oxigéngázzá bontják. Az eszköz különbsége abban rejlik, hogy megőrzi a keletkezett gázokat. A vízmolekulák oxidáció-redukciós reakción esnek át: a hidrogén redukálódik, oxigén oxidálódik. Az ily módon létrejövő gázok aránya kettő az egyikhez, mivel kétszer annyi hidrogéngáz keletkezik, mint oxigén. Amellett, hogy nem spontán, az elektrolízis fontos laboratóriumi eljárás.

  • 00:20:00 - 00:25:00

    Részletesen vizsgáltuk a víz elektrolíziséhez kapcsolódó félreakciókat. A redukció során vízmolekulák hidrogénatomjaiból hidrogéngáz képződik, míg az oxidáció során oxigénatomok alakulnak oxigéngázzá, miközben az elektronmozgalmakat az anód (oxidáció helyszíne) és a katód (redukció helyszíne) szabályozza. Ebben a szakaszban bemutattuk a részletes kémiai egyenleteket, amelyek kifejezik ezeket a részreakciókat, és összevontuk őket egy összesített reakcióvá.

  • 00:25:00 - 00:32:45

    Az elektrolízis eredménye a víz esetén egyensúlyozott kémiai egyenletet mutat, ahol a hidrogén gázzá redukálódik, oxigént oxidálnak, miközben vannak olyan jellemzők mint a gáz mennyiségének különbsége, amelyek az elektrolízis során keletkeznek. Az ilyen laboratóriumi eljárások világosan bemutatják, hogy a kémiai reakciók hogyan használhatják ki az elektromos energiát olyan átalakulások létrehozásához, amelyek spontán nem mennének végbe, mint a víz hidrogénra és oxigénre való bontása.

显示更多

思维导图

Mind Map

视频问答

  • Mi az elektrolízis?

    Az elektrolízis egy folyamat, amely során elektromosságot használnak kémiai változások előidézésére, amelyek önállóan nem történnének meg.

  • Milyen példák vannak az elektrolízisre?

    A videóban két példát említenek: a nátrium-klorid bontását nátriumfémre és klórgázra, valamint a víz bontását hidrogén- és oxigéngázra.

  • Miért nem történnek meg ezek a reakciók önmaguktól?

    Ezek a reakciók nem spontának, mivel a kiinduló anyagok (mint pl. a nátrium-klorid vagy a víz) stabil elektronkonfigurációval rendelkeznek, amelyeket nem hajlandók megváltoztatni külső beavatkozás nélkül.

  • Hogyan működik az elektrolízis a nátrium-kloridon?

    Elektromosságot használnak a nátrium-klorid (NaCl) bontására, ami nátriumfém (Na) és klórgáz (Cl2) képződéséhez vezet. A folyamat során a kloridionok (Cl-) oxidálódnak, míg a nátriumionok (Na+) redukálódnak.

  • Mire van szükség az elektrolízishez a víznél?

    A víz elektrolíziséhez szükség van valamilyen elektrolitra, például kénsavra (H2SO4), hogy vezesse az áramot a vízben.

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  • 00:00:00
    let's talk about the chemical process of
  • 00:00:03
    electrolysis I wanted to try to write
  • 00:00:05
    the simplest definition that I could so
  • 00:00:07
    here's what I came up with electrolysis
  • 00:00:10
    is a process where electricity is used
  • 00:00:13
    to make a chemical change happen that
  • 00:00:16
    wouldn't happen otherwise so we have
  • 00:00:19
    some kind of a chemical change that
  • 00:00:21
    doesn't happen on its own but then we
  • 00:00:24
    can use electricity to make that
  • 00:00:26
    chemical change happen now electrolysis
  • 00:00:30
    is often used to take a compound and
  • 00:00:33
    break it apart into the elements that
  • 00:00:36
    make it up we'll look at two examples of
  • 00:00:39
    that in this video first we'll look at
  • 00:00:43
    sodium chloride being broken apart by
  • 00:00:46
    electrolysis into sodium metal and
  • 00:00:48
    chlorine gas and just FYI this is an
  • 00:00:51
    unbalanced equation then we'll look at
  • 00:00:54
    an example of water being broken apart
  • 00:00:58
    using electrolysis into hydrogen gas and
  • 00:01:01
    oxygen gas so let's get started by
  • 00:01:03
    taking a look at this reaction so here's
  • 00:01:05
    unbalanced equation for the electris of
  • 00:01:08
    sodium chloride now sometimes people ask
  • 00:01:11
    me why is a cl2 and not CL well that's
  • 00:01:14
    because CL chlorine is one of the
  • 00:01:17
    datomic elements these are the diatomic
  • 00:01:19
    elements and the diatomic elements
  • 00:01:22
    always form groups of two they always
  • 00:01:25
    pair up together you never find Just One
  • 00:01:27
    of These atoms alone by itself so this
  • 00:01:30
    would never just be CL it would be cl2
  • 00:01:34
    instead so the equation we've got here
  • 00:01:37
    is an example of an oxidation reduction
  • 00:01:40
    reaction electrons are moving between
  • 00:01:43
    atoms in this equation I want to
  • 00:01:46
    understand how they're moving and where
  • 00:01:48
    they're moving and in order to do that
  • 00:01:50
    we got to write oxidation numbers for
  • 00:01:53
    the different elements in this equation
  • 00:01:55
    so check it out I got some information
  • 00:01:58
    here that will help us write oxidation
  • 00:01:59
    number for these elements we can do this
  • 00:02:01
    really quick so NaCl here is an ionic
  • 00:02:04
    compound sodium and chloride na is in
  • 00:02:07
    group 1 a so it is always plus one okay
  • 00:02:12
    CL chloride is one of the halogens here
  • 00:02:15
    usually minus one positive with oxygen
  • 00:02:18
    definitely minus one here and then on
  • 00:02:20
    this side of the equation we have sodium
  • 00:02:22
    and chlorine on their own they're
  • 00:02:25
    Elements by themselves they're not
  • 00:02:28
    bonded to any other elements so na over
  • 00:02:30
    here is going to be zero and cl2 over
  • 00:02:33
    here is going to be zero as well okay so
  • 00:02:37
    those are the oxidation numbers for
  • 00:02:39
    these elements now to understand how the
  • 00:02:43
    electrons move we got to take a look at
  • 00:02:46
    the changes in these oxidation numbers
  • 00:02:49
    we'll use this information to help us
  • 00:02:51
    out so let's take a look at sodium here
  • 00:02:54
    na on this side of the equation it's
  • 00:02:56
    plus one and then over here it's zero so
  • 00:03:01
    its oxidation number goes down so that
  • 00:03:04
    means that it is undergoing reduction it
  • 00:03:07
    is gaining electrons so sodium is
  • 00:03:10
    reduced here from + one to zero and then
  • 00:03:14
    CL goes from minus1 here to zero over
  • 00:03:18
    here so its oxidation number is going up
  • 00:03:21
    it is undergoing oxidation and it is
  • 00:03:25
    losing electrons it's being oxidized
  • 00:03:27
    from minus1 to zero so sodium is reduced
  • 00:03:33
    gaining electrons and chloride is
  • 00:03:36
    oxidized losing electrons now there's
  • 00:03:39
    something really important about this
  • 00:03:41
    process and that's that this process
  • 00:03:44
    doesn't happen on its own sodium
  • 00:03:47
    chloride is also known as table salt and
  • 00:03:50
    you could keep table salt in your
  • 00:03:52
    kitchen for hundreds of years and it's
  • 00:03:55
    never going to separate out into sodium
  • 00:03:58
    and chlorine gas
  • 00:04:00
    it's just not going to happen this
  • 00:04:01
    process doesn't happen on its own by
  • 00:04:04
    itself to use chemistry terms we can say
  • 00:04:07
    that this process is not spontaneous
  • 00:04:11
    spontaneous process is something that
  • 00:04:13
    happens on its own now a big part of the
  • 00:04:16
    reason why this isn't a spontaneous
  • 00:04:18
    reaction is because sodium and chloride
  • 00:04:21
    over here are really happy with the
  • 00:04:24
    number of electrons that they have
  • 00:04:26
    sodium doesn't want to gain more
  • 00:04:29
    electrons and chloride here doesn't want
  • 00:04:31
    to lose electrons they're totally set
  • 00:04:34
    right here so we have to force this
  • 00:04:37
    process to happen and that's where the
  • 00:04:39
    electricity part of electrolysis comes
  • 00:04:42
    into play the electrical energy from a
  • 00:04:46
    battery can force this process to happen
  • 00:04:50
    so here's our battery and a battery has
  • 00:04:53
    these two sides the positive and
  • 00:04:56
    negative the positive side of the
  • 00:04:59
    battery pulls electrons in and the
  • 00:05:02
    negative side of the battery pushes
  • 00:05:06
    electrons out so these two things can
  • 00:05:10
    force this process to happen so chloride
  • 00:05:15
    doesn't want to lose its electrons but
  • 00:05:18
    you know what the positive side of the
  • 00:05:20
    battery just pulls electrons away from
  • 00:05:22
    it right it's like you don't want to
  • 00:05:24
    lose these electrons tough I'm just
  • 00:05:26
    going to pull them away from you and the
  • 00:05:28
    negative side of the battery that pushes
  • 00:05:30
    electrons out it's going to push
  • 00:05:33
    electrons to sodium sodium doesn't want
  • 00:05:35
    to gain electrons too bad the negative
  • 00:05:38
    side of the battery is going to push
  • 00:05:40
    electrons to the sodium making this
  • 00:05:42
    process happen so now I want to show you
  • 00:05:46
    the device that we use to do
  • 00:05:50
    electrolysis and make this process
  • 00:05:52
    happen and then I want to use our Atomic
  • 00:05:55
    Vision to see the atoms and electrons
  • 00:05:58
    and how they move during this
  • 00:06:01
    electrolysis process so here's a picture
  • 00:06:03
    of the device that we use to make this
  • 00:06:05
    process happen this is called an
  • 00:06:07
    electrolytic cell and it's got a couple
  • 00:06:09
    of different parts first we got this
  • 00:06:11
    container that's full of the sodium
  • 00:06:14
    chloride then we got a battery and the
  • 00:06:17
    two sides of the battery are hooked up
  • 00:06:19
    to what we call
  • 00:06:21
    electrodes the electrodes put electrons
  • 00:06:24
    into the sodium chloride and they pull
  • 00:06:27
    the electrons out
  • 00:06:30
    and then finally the sodium chloride
  • 00:06:31
    here it's not just like the powdered
  • 00:06:34
    table salt that you're used to from the
  • 00:06:36
    kitchen this has got to be molten liquid
  • 00:06:41
    melted sodium chloride sodium chloride
  • 00:06:44
    doesn't melt until about 1500° fahr or
  • 00:06:48
    800° C so it's got to be super super hot
  • 00:06:53
    and this device has to withstand really
  • 00:06:55
    high temperatures the sodium chloride
  • 00:06:57
    has got to be molten for the
  • 00:06:59
    electrolysis to happen now let's zoom in
  • 00:07:02
    on this a little bit more if we could
  • 00:07:04
    zoom in to the sodium chloride millions
  • 00:07:07
    and millions of times this is what we'd
  • 00:07:10
    see the sodium chloride is molten or
  • 00:07:13
    liquid which means the sodium and the
  • 00:07:16
    chloride ions have come apart from each
  • 00:07:18
    other and they're in constant motion
  • 00:07:22
    moving around in this container now here
  • 00:07:26
    are the electrodes this is that one and
  • 00:07:29
    this this is that one these electrodes
  • 00:07:31
    in the diagram here are way way way
  • 00:07:34
    closer together than they should be
  • 00:07:35
    based on this this is definitely not to
  • 00:07:37
    scale but I wanted you to be able to see
  • 00:07:40
    both of the electrodes now there's
  • 00:07:42
    another important part of this
  • 00:07:44
    electrolytic cell and that is the
  • 00:07:48
    battery the diagram that I put here
  • 00:07:52
    shows the direction that electrons move
  • 00:07:54
    electrons move from here into the
  • 00:07:56
    battery and then out of the battery into
  • 00:07:59
    this electrode so we can give names to
  • 00:08:02
    these two electrodes based on how the
  • 00:08:06
    electrons are moving okay the electrode
  • 00:08:09
    over here we call the anode the anode is
  • 00:08:12
    the site of oxidation oxidation is
  • 00:08:16
    happening in here because the anode is
  • 00:08:18
    pulling in electrons because this is the
  • 00:08:21
    direction the electrons move now over
  • 00:08:23
    here we have the cathode reduction
  • 00:08:28
    happens to the cathode the cathode
  • 00:08:30
    pushes out electrons because this is the
  • 00:08:34
    direction that electrons are moving from
  • 00:08:35
    the battery so we got the anode and the
  • 00:08:38
    cathode we got the battery the
  • 00:08:40
    electrodes and the sodium chloride we're
  • 00:08:43
    ready to do some electrolysis I'm going
  • 00:08:45
    to get rid of a few of these ions to
  • 00:08:47
    make the process a little bit clearer
  • 00:08:49
    okay that's a little bit clearer so now
  • 00:08:52
    we hook the battery up to the electrodes
  • 00:08:54
    and this is what happens so this cathode
  • 00:08:58
    here is connected to the negative side
  • 00:08:59
    of the battery so that means that it's
  • 00:09:01
    going to have a negative charge these
  • 00:09:04
    positively charged sodium atoms are
  • 00:09:06
    going to be attracted to the negatively
  • 00:09:08
    charged cathode because opposite charges
  • 00:09:10
    attract so we got this na+ moving over
  • 00:09:14
    to the negatively charged cathode and
  • 00:09:17
    electrons as we said are being pushed
  • 00:09:20
    out of the battery into the cathode and
  • 00:09:23
    this electron is going to be given to
  • 00:09:27
    the na+ ion and gaining that electron is
  • 00:09:31
    going to get rid of the charge on that
  • 00:09:35
    na so it's going to turn this into an
  • 00:09:37
    neutral sodium atom the same thing is
  • 00:09:40
    going to happen to this one over here
  • 00:09:42
    it's got a positive charge it's
  • 00:09:43
    attracted to the negative cathode moves
  • 00:09:47
    over here an electron gets pushed from
  • 00:09:50
    the battery it goes into the sodium ion
  • 00:09:54
    and gaining that electron causes the
  • 00:09:58
    sodium to lose it charge so now we have
  • 00:10:01
    two neutrally charged sodium atoms now
  • 00:10:06
    over here at the anode the opposite
  • 00:10:09
    thing is going to happen electrons are
  • 00:10:11
    going to be pulled out of these ions so
  • 00:10:15
    we got this chloride over here it's
  • 00:10:18
    attracted to the anode because the anode
  • 00:10:20
    is hooked up to the positive side of the
  • 00:10:22
    battery and this is negatively charged
  • 00:10:24
    so it's going to be pulled over here and
  • 00:10:26
    the anode is pulling in electrons so one
  • 00:10:29
    of the electrons from the CL minus is
  • 00:10:32
    going to be pulled up towards the
  • 00:10:34
    battery and that is going to cause the
  • 00:10:37
    negative charge to go away because it's
  • 00:10:39
    lost one of its electrons and then over
  • 00:10:42
    here this CL minus is also going to get
  • 00:10:45
    attracted to the anode it's going to
  • 00:10:47
    lose one of its electrons it's going to
  • 00:10:49
    get pulled up here towards the battery
  • 00:10:52
    and that is going to cause this to lose
  • 00:10:55
    its negative charge now we said that
  • 00:10:58
    chlorine here is one of the datomic
  • 00:11:00
    elements so that means that we're never
  • 00:11:02
    just going to find one of these atoms on
  • 00:11:06
    their own as soon as they don't have a
  • 00:11:09
    charge anymore they're going to pair up
  • 00:11:12
    to form a cl2 molecule this is gas and
  • 00:11:16
    it's actually going to float away so
  • 00:11:19
    that's how the electrons move in this
  • 00:11:22
    electrolytic cell here's a diagram of
  • 00:11:24
    the process that I just showed you I
  • 00:11:26
    want to use this to write half reactions
  • 00:11:30
    for what's going on at the anode and the
  • 00:11:32
    cathode so oxidation happens at the
  • 00:11:35
    anode and reduction happens at the
  • 00:11:38
    cathode let's write these half reactions
  • 00:11:40
    so over here at the cathode we start out
  • 00:11:43
    with na 1+ that gains an electron plus e
  • 00:11:48
    minus the symbol for
  • 00:11:50
    electron and that gives us neutral
  • 00:11:53
    sodium na without a charge that's how we
  • 00:11:56
    know it's neutral now over here at the
  • 00:11:59
    oxidation half reaction I'm going to
  • 00:12:02
    write this a little bit incorrectly
  • 00:12:04
    first and then I'm going to fix it okay
  • 00:12:06
    so here we start out with two cl1 minus
  • 00:12:10
    okay two CL minus and then what happens
  • 00:12:14
    is these lose two electrons one two get
  • 00:12:18
    pulled up to the battery so I'm going to
  • 00:12:20
    write minus 2 e minus that's incorrect
  • 00:12:23
    but I'll fix it in a minute and that
  • 00:12:25
    gives us a molecule of cl2 to gas now
  • 00:12:30
    what's wrong about this well you can't
  • 00:12:33
    subtract things in a chemical equation
  • 00:12:35
    even though it makes a lot of sense so
  • 00:12:37
    to make this correct I have to put these
  • 00:12:39
    two electrons on the other side of the
  • 00:12:43
    chemical equation so here is the correct
  • 00:12:45
    version where I've just moved the
  • 00:12:47
    electrons over here and this is the
  • 00:12:50
    correct way to write the oxidation half
  • 00:12:53
    reaction now that I've written the
  • 00:12:55
    oxidation and reduction half reactions I
  • 00:12:57
    want to show you how we can put them
  • 00:12:59
    together to get a reaction for this
  • 00:13:01
    whole process now let's combine these
  • 00:13:03
    half reactions that we just wrote In
  • 00:13:05
    order to add or combine these half
  • 00:13:07
    reactions together they have to have the
  • 00:13:09
    same number of electrons but they don't
  • 00:13:12
    right now there's one electron here and
  • 00:13:15
    two electrons here so to fix that I'm
  • 00:13:18
    going to take this reduction half
  • 00:13:19
    reaction and I'm just going to multiply
  • 00:13:21
    it by two just like it's a math equation
  • 00:13:25
    and that is going to give me this new
  • 00:13:28
    reaction action I've just put a two in
  • 00:13:31
    front of everything Distributing it
  • 00:13:33
    across the reaction okay so there's my
  • 00:13:36
    new reduction half reaction and then
  • 00:13:38
    here's my oxidation half reaction now
  • 00:13:40
    that they have the same number of
  • 00:13:42
    electrons I can add them together and
  • 00:13:44
    this is what I get I take everything on
  • 00:13:48
    this side of the arrow and put it on one
  • 00:13:50
    side I have my na my two electrons and
  • 00:13:53
    my 2 CL on this side and then on this
  • 00:13:56
    side I have my na my cl2 and my 2 e
  • 00:14:01
    minus now there's still a little bit
  • 00:14:03
    more that I have to do before this
  • 00:14:05
    equation is totally finished if there's
  • 00:14:08
    anything on both sides of the arrow we
  • 00:14:10
    cancel it out so there two electrons
  • 00:14:12
    here and two electrons here I'll cancel
  • 00:14:14
    those out and then I have 2 na+ here and
  • 00:14:19
    I have two CL minus here I can combine
  • 00:14:23
    those together to make
  • 00:14:26
    NA so my final equation is going to look
  • 00:14:29
    like this 2 NAC and then on this side 2
  • 00:14:33
    na plus cl2 and you'll notice that I've
  • 00:14:37
    also put in these parentheses to show
  • 00:14:40
    the physical state of each of these
  • 00:14:43
    particular compounds this is liquid
  • 00:14:45
    because it's so hot it's molten the na
  • 00:14:48
    is also liquid because it's so hot and
  • 00:14:51
    the cl2 is gas and just floats away so
  • 00:14:54
    let's just pull everything together that
  • 00:14:56
    we talked about here is our final
  • 00:14:58
    equation for the the electrolysis of
  • 00:15:00
    sodium chloride this happens because
  • 00:15:03
    sodium gains electrons and is reduced
  • 00:15:07
    this happens at the cathode in the
  • 00:15:08
    electrolytic cell which pushes out
  • 00:15:11
    electrons it's where reduction takes
  • 00:15:13
    place and it's where sodium gains these
  • 00:15:16
    electrons here is the half reaction for
  • 00:15:18
    the reduction of
  • 00:15:20
    sodium then chloride loses electrons it
  • 00:15:25
    undergoes oxidation and this happens at
  • 00:15:27
    the anode in the electrolytic cell the
  • 00:15:30
    anode pulls in electrons oxidation
  • 00:15:33
    happens there and here is the half
  • 00:15:35
    reaction for chloride losing electrons
  • 00:15:39
    and getting oxidized so that's how
  • 00:15:43
    sodium chloride turns into sodium and
  • 00:15:46
    chlorine gas during electrolysis here's
  • 00:15:50
    another Super common example the
  • 00:15:52
    electrolysis of water we take water H2O
  • 00:15:56
    add some electrical energy and we get
  • 00:15:58
    high hen and oxygen gas you might be
  • 00:16:01
    able to tell this is a balanced equation
  • 00:16:03
    because I think you guys can handle it
  • 00:16:06
    now what's with H2 and O2 here well
  • 00:16:10
    hydrogen and oxygen just like chlorine
  • 00:16:13
    which we saw earlier are examples of the
  • 00:16:15
    datomic elements you'll never find just
  • 00:16:18
    an H or an O alone by itself these
  • 00:16:22
    elements always pair up and form twos so
  • 00:16:26
    that's why we got H2 and O2 here now
  • 00:16:30
    this equation represents an oxidation
  • 00:16:33
    reduction process so electrons are
  • 00:16:35
    moving they're being transferred let's
  • 00:16:38
    figure out how they're being transferred
  • 00:16:40
    by looking at the oxidation numbers I've
  • 00:16:43
    got some rules for writing oxidation
  • 00:16:45
    numbers here these are just a few of
  • 00:16:46
    them these are just the ones that are
  • 00:16:47
    relevant to the equation that I'm
  • 00:16:49
    talking about here okay so I've got
  • 00:16:52
    hydrogen hydrogen is + one when it's
  • 00:16:56
    with non-metals like oxygen oxygen is
  • 00:16:58
    usually
  • 00:17:01
    -2 and then over here we have hydrogen
  • 00:17:04
    and oxygen these are elements by
  • 00:17:06
    themselves they're not combined with any
  • 00:17:08
    other elements so H2 is going to be zero
  • 00:17:12
    and O2 is going to be zero okay so those
  • 00:17:14
    are the oxidation numbers and now to see
  • 00:17:17
    how the electrons are being transferred
  • 00:17:19
    let's look at the change in oxidation
  • 00:17:21
    number okay starting here with hydrogen
  • 00:17:24
    hydrogen is + one and then over on this
  • 00:17:27
    side of the equation it is z Z so its
  • 00:17:29
    oxidation number is going down which
  • 00:17:32
    means that it is undergoing reduction it
  • 00:17:35
    is gaining
  • 00:17:38
    electrons Ox uh oxygen over here is
  • 00:17:43
    min-2 and then on the right side of the
  • 00:17:45
    equation it is zero so Oxygen's
  • 00:17:49
    oxidation number is going up from min-2
  • 00:17:52
    to 0 oxidation number going up that
  • 00:17:55
    means it is undergoing oxidation which
  • 00:17:57
    is loss of el electrons so oxygen is
  • 00:18:00
    being
  • 00:18:02
    oxidized it is losing electrons here
  • 00:18:06
    this process is important because just
  • 00:18:08
    like we saw in the previous example with
  • 00:18:11
    sodium chloride this process doesn't
  • 00:18:14
    happen on its own it's not spontaneous
  • 00:18:17
    you can have water in a glass for
  • 00:18:20
    hundreds of years if it doesn't
  • 00:18:22
    evaporate and it's not going to turn
  • 00:18:25
    into hydrogen gas and oxygen gas it's
  • 00:18:27
    just not going to do that on its zone so
  • 00:18:29
    just like the previous example we're
  • 00:18:31
    going to have to use the electrical
  • 00:18:33
    energy from a battery to force this
  • 00:18:36
    process to happen so now let's take a
  • 00:18:39
    look at the device that we'd use to do
  • 00:18:41
    electrolysis of water it looks a little
  • 00:18:44
    bit different than the device we talked
  • 00:18:46
    about earlier because often when we do
  • 00:18:49
    electrolysis of water we want to be able
  • 00:18:51
    to keep or hold on to the oxygen gas and
  • 00:18:54
    the hydrogen gas that get produced so
  • 00:18:56
    this is the electrolytic cell that we'd
  • 00:18:59
    use to do the electrolysis of water
  • 00:19:02
    here's what's going on we have a
  • 00:19:04
    container that has water in it and then
  • 00:19:07
    we got these weird looking things here
  • 00:19:09
    what are these well these are actually
  • 00:19:12
    test tubes that are filled with water
  • 00:19:15
    and are put upside down in the top of
  • 00:19:18
    this container so it's like you'd fill
  • 00:19:20
    them with water and then you'd very
  • 00:19:22
    carefully turn them upside down so
  • 00:19:24
    they're still filled with water and
  • 00:19:26
    they're in the container then just like
  • 00:19:28
    in the previous example we've got these
  • 00:19:30
    electrodes here the electrodes are in
  • 00:19:34
    the test tubes you can see that they're
  • 00:19:35
    like sticking in the test tubes and the
  • 00:19:37
    electrodes are hooked up to the battery
  • 00:19:40
    it's the electrodes that are putting
  • 00:19:42
    electrons into the water or pulling
  • 00:19:44
    electrons out of the water okay and then
  • 00:19:47
    finally of course we have the water now
  • 00:19:50
    I should say this electrolysis process
  • 00:19:52
    doesn't just happen in distilled pure
  • 00:19:55
    water we got to add a little something
  • 00:19:57
    like like like sulfuric acid here to
  • 00:20:01
    allow electricity to flow through the
  • 00:20:04
    water so you can't just do this in pure
  • 00:20:06
    water got to add what we call an
  • 00:20:07
    electrolyte like h2so4 sulfuric acid
  • 00:20:12
    okay now let's look at how these
  • 00:20:14
    electrodes here are connected to the
  • 00:20:16
    battery okay this electrode here is
  • 00:20:20
    hooked up to the negative side of the
  • 00:20:22
    battery so electrons as you can see here
  • 00:20:24
    are moving out of the negative side and
  • 00:20:26
    they're being pushed into this electrode
  • 00:20:29
    so that means that this is the cathode
  • 00:20:32
    it's the site of
  • 00:20:34
    reduction over here this electode is
  • 00:20:38
    hooked up to the positive side of the
  • 00:20:39
    battery so electrons are moving out of
  • 00:20:42
    it that means that oxidation is going to
  • 00:20:46
    be taking place it's going to be pulling
  • 00:20:48
    electrons from things and this is what
  • 00:20:50
    we call the anode so we've got hydrogen
  • 00:20:54
    gas and oxygen gas what gets made where
  • 00:20:58
    well well hydrogen here in water gets
  • 00:21:01
    reduced to form hydrogen gas so the
  • 00:21:06
    cathode the site of reduction is going
  • 00:21:08
    to be where hydrogen gas gets produced
  • 00:21:12
    H2 produced here at the cathode and then
  • 00:21:16
    oxygen in water gets oxidized to form
  • 00:21:21
    oxygen gas so over here at the anode the
  • 00:21:24
    site of oxidation oxygen is going to be
  • 00:21:27
    produced so we hook everything together
  • 00:21:30
    we add little sulfuric acid to the water
  • 00:21:32
    connect the electrodes to the battery
  • 00:21:34
    and we'll start seeing bubbles that's
  • 00:21:37
    the gas being formed on the electrodes
  • 00:21:41
    and those bubbles are going to start
  • 00:21:44
    moving up to the top of the test tubes
  • 00:21:47
    and if you look carefully you see a
  • 00:21:49
    really cool thing happen the level of
  • 00:21:52
    the water starts to go down because gas
  • 00:21:57
    is flowing up it's floating up and it's
  • 00:22:00
    collecting at the top of the test tubes
  • 00:22:02
    and it's forcing the water down so you
  • 00:22:06
    see the water level slowly move down as
  • 00:22:10
    the gas collects at the top of the test
  • 00:22:15
    tubes it's really cool and you can watch
  • 00:22:16
    this you can see this happen in the lab
  • 00:22:19
    now something else really interesting
  • 00:22:21
    happens you'll see what I did here and I
  • 00:22:24
    I'm not just being careless on the side
  • 00:22:27
    that's producing hydrogen
  • 00:22:29
    you get twice as much gas as the side
  • 00:22:33
    that's producing oxygen there's twice as
  • 00:22:36
    much hydrogen gas as oxygen gas why is
  • 00:22:39
    that well take a look at this balanced
  • 00:22:42
    equation here okay we have 2 H2 and just
  • 00:22:46
    1 O2 so there is a 2: one ratio of
  • 00:22:52
    hydrogen gas to oxygen gas so that means
  • 00:22:56
    that when we do this electrolysis we are
  • 00:22:58
    physically going to get twice as much
  • 00:23:01
    much hydrogen gas in this test tube as
  • 00:23:04
    we get oxygen gas over here okay so
  • 00:23:08
    that's the big picture of how we do
  • 00:23:11
    electrolysis in the lab and what's going
  • 00:23:13
    on here in the electrolytic cell now
  • 00:23:15
    let's take a look at the half reactions
  • 00:23:18
    for the reduction of hydrogen and the
  • 00:23:20
    oxidation of oxygen let's break this
  • 00:23:22
    process down into the two half reactions
  • 00:23:25
    that make it up now let me just tell you
  • 00:23:27
    when it comes to writing half reactions
  • 00:23:29
    for the electrolysis of water there are
  • 00:23:31
    so many different ways to do it and it
  • 00:23:34
    seems like every textbook or every
  • 00:23:36
    teacher has their own way of writing
  • 00:23:38
    these half reactions in this video I'm
  • 00:23:40
    using the half reactions that I think
  • 00:23:42
    make most sense but if you're teacher or
  • 00:23:45
    textbook has a way they really want you
  • 00:23:47
    to do it instead just learn their method
  • 00:23:50
    every way of writing these is
  • 00:23:52
    essentially equivalent they're
  • 00:23:53
    essentially the same they just look a
  • 00:23:55
    little bit different so again I'm using
  • 00:23:57
    the reactions that I think make most
  • 00:23:59
    sense for this video let's start with a
  • 00:24:01
    reduction of hydrogen I really want to
  • 00:24:03
    show you what's going on with the atoms
  • 00:24:05
    and electrons in these half reactions
  • 00:24:07
    okay so we start with two molecules of
  • 00:24:11
    water H2O and you'll see that I've
  • 00:24:12
    written oxidation numbers above each of
  • 00:24:15
    the atoms so in the reduction of
  • 00:24:18
    hydrogen essentially what happens is
  • 00:24:20
    it's like we take one hydrogen from each
  • 00:24:23
    of these water molecules and pull them
  • 00:24:25
    off and then we combine them to make a
  • 00:24:29
    molecule of H2 hydrogen gas now what has
  • 00:24:33
    to happen with the electrons for this to
  • 00:24:36
    take place well each of the hydrogens
  • 00:24:39
    over here has an oxidation number of
  • 00:24:41
    plus one but then they have an oxidation
  • 00:24:44
    number of zero over here so that means
  • 00:24:47
    that each of these hydrogens has to gain
  • 00:24:50
    one electron so that its oxidation
  • 00:24:53
    number can be bumped up by one okay
  • 00:24:56
    here's here's a diagram sort of showing
  • 00:24:58
    what happening here okay this hydrogen
  • 00:25:01
    was plus one and then it gains an
  • 00:25:03
    electron and becomes zero this hydrogen
  • 00:25:06
    was plus one and it gained an electron
  • 00:25:09
    and became zero where do these electrons
  • 00:25:11
    come from in the electrolytic cell well
  • 00:25:13
    they came from the cathode because the
  • 00:25:16
    cathode is what pushes out electrons the
  • 00:25:19
    cathode is where reduction happens okay
  • 00:25:22
    so we get one molecule of H2 but then we
  • 00:25:26
    have these parts of the water molecule
  • 00:25:28
    which you're just left behind so we get
  • 00:25:30
    an O and an h and these two things
  • 00:25:33
    together have a negative charge of one
  • 00:25:35
    minus these are polyatomic ions are
  • 00:25:38
    called a hydroxide ion and the reason
  • 00:25:40
    why they have a charge here is because
  • 00:25:42
    notice that their oxidation numbers
  • 00:25:45
    haven't changed because we're not adding
  • 00:25:47
    or removing electrons from the rest of
  • 00:25:50
    the water molecule so these numbers are
  • 00:25:53
    just staying the same as they were over
  • 00:25:56
    here you add these oxidation numbers up
  • 00:25:59
    and you getus oneus one so that's the
  • 00:26:02
    charge of this ion okay so this is how
  • 00:26:06
    the reduction happens with
  • 00:26:08
    pictures let's look at how we can
  • 00:26:10
    actually write an equation actual half
  • 00:26:13
    reaction for what's going on here we
  • 00:26:15
    start with two molecules of H2O then we
  • 00:26:19
    gain two electrons so plus 2 e
  • 00:26:23
    minus and that gives us one molecule of
  • 00:26:26
    H2 and then get two o
  • 00:26:31
    minus so that's the half reaction here
  • 00:26:34
    that's a half reaction for the reduction
  • 00:26:35
    of hydrogen now let's take a look at the
  • 00:26:38
    half reaction for the oxidation of
  • 00:26:41
    oxygen okay just like up here we start
  • 00:26:45
    with two molecules of
  • 00:26:49
    H2O and for the oxidation of oxygen it's
  • 00:26:52
    going to be like we pull off these two
  • 00:26:55
    oxygen
  • 00:26:56
    atoms to make a molecule of o2 oxygen
  • 00:26:59
    gas now how about the electrons in this
  • 00:27:02
    case well both of these oxygen were
  • 00:27:05
    minus two for their oxidation number
  • 00:27:07
    over here and then they became zero over
  • 00:27:09
    here so each one of them has to
  • 00:27:14
    lose two electrons to become zero this
  • 00:27:19
    one was minus two then it loses two
  • 00:27:21
    electrons become zero this one was minus
  • 00:27:24
    two it lost two electrons to bump its
  • 00:27:26
    oxidation number up it's losing
  • 00:27:28
    electrons to zero so that's what's going
  • 00:27:32
    on here now where are these electrons
  • 00:27:36
    going well the electrons are going to
  • 00:27:40
    the anode because it's the anode and
  • 00:27:43
    oxidation reduction reactions that is
  • 00:27:46
    pulling in electrons okay so this is
  • 00:27:50
    what's happening with the oxygen what
  • 00:27:52
    about the rest of this well we have four
  • 00:27:54
    hydrogens left over after we pull off
  • 00:27:57
    those oxygens and their oxidation
  • 00:27:59
    numbers are not changing because we're
  • 00:28:01
    not adding or removing electrons so
  • 00:28:04
    we're just going to get four
  • 00:28:07
    H+ over here left over that have an
  • 00:28:10
    oxidation number of plus one because
  • 00:28:12
    that's not changing let's do the same
  • 00:28:14
    thing that we did up here let's write a
  • 00:28:17
    half reaction for the process this is a
  • 00:28:19
    little bit more challenging as before
  • 00:28:21
    I'm going to write it incorrectly first
  • 00:28:23
    and then we're going to fix it okay so
  • 00:28:24
    we start with 2 H2O
  • 00:28:28
    and then we lose four electrons -2 -2 so
  • 00:28:34
    -4
  • 00:28:36
    electrons and that gives
  • 00:28:38
    us O2 +
  • 00:28:42
    4 h plus these up here now as you
  • 00:28:46
    probably know we can't use the
  • 00:28:48
    subtraction sign in a chemical equation
  • 00:28:51
    so we have to make this four electrons
  • 00:28:55
    and put it over here so this is what
  • 00:28:57
    we're going to yet instead we just move
  • 00:29:00
    this four electrons over here 4 e minus
  • 00:29:03
    there we
  • 00:29:04
    go okay there we go now we can see it
  • 00:29:07
    and these are the half reactions for the
  • 00:29:09
    reduction of hydrogen and the oxidation
  • 00:29:12
    of oxygen now let's combine them put
  • 00:29:15
    them together okay now so for combining
  • 00:29:17
    these half reactions we want them to
  • 00:29:19
    have the same number of electrons the
  • 00:29:22
    reduction half reaction that only has
  • 00:29:23
    two electrons we have four here so the
  • 00:29:26
    way we're going to solve this is we're
  • 00:29:27
    going to take this whole equation and
  • 00:29:30
    we're going to multiply it by two and
  • 00:29:33
    distributing this two across the
  • 00:29:35
    equation we are going to end up with
  • 00:29:38
    this 4 H2O four electrons 2 H2 and 4 oh
  • 00:29:43
    minus so that is our new reduction half
  • 00:29:46
    reaction now we can take these two half
  • 00:29:50
    reactions and add them together we're
  • 00:29:52
    going to get this we take everything
  • 00:29:54
    from this side of the equation and put
  • 00:29:56
    it here 4 H2O 4 4 e minus 2 H2O then we
  • 00:30:00
    have our arrow and then we have 2
  • 00:30:03
    H2 4 oh minus O2 + 4
  • 00:30:08
    h++ 4 e minus all right now there are a
  • 00:30:13
    few things that we can do here if
  • 00:30:14
    something appears on both sides of the
  • 00:30:18
    uh of the arrow here we can cancel it
  • 00:30:19
    out okay so we'll get rid of this one
  • 00:30:21
    and we'll get rid of this one but that's
  • 00:30:23
    not all we can do look at this we have
  • 00:30:25
    four o minus here and we have 4
  • 00:30:29
    H+ oh minus and H+ combine to make water
  • 00:30:35
    now also look at this we have four H2O
  • 00:30:38
    here and 2 H2O here so we can combine
  • 00:30:42
    these to get six H2O all right so here's
  • 00:30:48
    how we can rewrite it we pull these
  • 00:30:51
    together and get 6 H2O we get rid of the
  • 00:30:53
    electrons there and then we have 2 H2 we
  • 00:30:57
    combine 4 oh minus and 4 H+ to get 4 H2O
  • 00:31:01
    and then we have our oxygen but you know
  • 00:31:04
    what there's actually one more thing we
  • 00:31:06
    can do because look we have H2O on both
  • 00:31:08
    sides of the equation so I can subtract
  • 00:31:12
    it so we can get rid of it from one side
  • 00:31:14
    I'm going to do Min -4 H2O here I'm
  • 00:31:17
    going to do minus 4 H2O here that's
  • 00:31:21
    completely going to get rid of the H2O
  • 00:31:23
    on this side and it's going to leave me
  • 00:31:25
    with 6 - 4 2
  • 00:31:28
    H2O on this side here is the same
  • 00:31:31
    balanced equation that we used when we
  • 00:31:33
    started you put the half reactions
  • 00:31:35
    together and this is what you get so
  • 00:31:37
    that is the electrolysis of water
  • 00:31:39
    hydrogen is reduced it gains electrons
  • 00:31:43
    this happens at the cathode the sight of
  • 00:31:44
    reduction and H2 is produced there then
  • 00:31:48
    oxygen is oxidized it loses electrons
  • 00:31:52
    this happens at the anode the site of
  • 00:31:54
    oxidation where the oxygen is produced
  • 00:31:57
    we got these two electrodes in these
  • 00:32:00
    upside down test tubes and the gas the
  • 00:32:03
    hydrogen and oxygen collects at the top
  • 00:32:06
    and we've seen that we get twice as much
  • 00:32:09
    hydrogen gas as oxygen and that's just
  • 00:32:11
    because in our balanced chemical
  • 00:32:13
    equation there's a ratio of two
  • 00:32:15
    hydrogens to one oxygen so that is why
  • 00:32:19
    we get twice as much hydrogen here as
  • 00:32:22
    oxygen here so that's how electrolysis
  • 00:32:25
    works that's how you put electrical
  • 00:32:27
    energy into a chemical reaction to make
  • 00:32:30
    something happen that wouldn't happen
  • 00:32:32
    otherwise something like taking sodium
  • 00:32:34
    chloride and breaking it apart into
  • 00:32:36
    sodium metal and chlorine gas or
  • 00:32:38
    something like taking water and
  • 00:32:41
    splitting it apart into hydrogen gas and
  • 00:32:43
    oxygen gas
标签
  • elektrolízis
  • kémiai reakciók
  • elektromosság
  • nátrium-klorid
  • oxidáció-redukció
  • vízbontás
  • elektrokémia
  • energia felhasználás
  • elemzés