IGCSE Chemistry Edexcel Ch 17 Metals - Dr. Hanaa Assil

00:47:03
https://www.youtube.com/watch?v=OwCKa24NN_o

Summary

TLDREl vídeo tracta sobre les propietats físiques i químiques dels metalls, centrant-se en la seva estructura única composta per ions positius i electrons lliures. Es destaca que els metalls són bons conductors elèctrics, brillants, maleables i dúctils. S'expliquen les reaccions dels metalls amb l'oxigen, aigua i àcids, ressaltant la importància de la sèrie de reactivitat per anticipar el comportament dels metalls en aquests processos. També es discuteixen maneres de prevenir la corrosió, com el galvanitzat, que protegeix els metalls mitjançant una capa de zinc que es corroeix en lloc de l'ferro. Alhora, es destaca l'ús de la protecció sacrificial i altres mètodes com recobrir amb plàstic o oli per evitar que el metall s'oxidi.

Takeaways

  • 🌐 Els metalls tenen una estructura tridimensional amb ions positius i electrons lliures.
  • ⚡ Tots els metalls condueixen l'electricitat gràcies als seus electrons delocalitzats.
  • 🔧 Els metalls són maleables i dúctils, permetent diverses aplicacions industrials.
  • 🔥 La reactivitat dels metalls depèn de la seva posició en la sèrie de reactivitat.
  • 🛡️ La corrosió es pot prevenir amb mètodes com la pintura, oli, plàstic o galvanització.
  • 🧪 Els metalls reactius, com el sodi, formen hidròxids i alliberen hidrogen amb aigua.
  • 🔍 La reacció de metalls amb vapor forma òxids en lloc d'hidròxids.
  • 🌊 Els metalls menys reactius no reaccionen amb àcids, com el coure.
  • 🔄 Els metalls més reactius tendeixen a corroejar més ràpidament en presència d'aigua o àcids.
  • 🥇 El rovell del ferro és òxid de ferro(III) hidratat, resultant de la seva oxidació.

Timeline

  • 00:00:00 - 00:05:00

    En aquest capítol, es discuteixen les propietats físiques i químiques dels metalls. Comença recordant l'estructura dels metalls, destacant que tenen una estructura gegant tridimensional amb ions positius regularment ordenats envoltats per electrons deslocalitzats. Es destaca la capacitat de conduir electricitat, ser maleables i dúctils, a causa dels electrons lliures i la capacitat dels ions per deslizar-los durant l'escalfament o el martelleig.

  • 00:05:00 - 00:10:00

    L'explicació continua amb la sèrie de reactivitat química dels metalls, que és una classificació basada en la reactivitat de cadascun. S'explica com els metalls del Grup 1 són més reactius, i es proporcionen exemples com la reactivitat superior del potassi respecte al sodi. També s'inclou com la reactivitat pot deduir-se de la taula periòdica i com els continguts canviants al descendre dins del mateix grup influeixen en la reactivitat.

  • 00:10:00 - 00:15:00

    Es presenten les reaccions dels metalls amb oxigen, il·lustrant com la combustió de metalls com el magnesi en oxigen produeix òxids metàl·lics, explicant les observacions com la flama intensa i el sòlid blanc resultant. A més, s'introdueix el concepte d'òxids amfòtics que poden actuar com àcids i bases, exemplificant amb el òxid de magnesi. Se segueix amb mètodes de reacció per descobrir masses en laboratoris.

  • 00:15:00 - 00:20:00

    La reacció dels metalls amb aigua es discuteix detalladament, explicant com elements com el liti i el potassi canvien d'aspecte quan es tallen i s'exposen a l'aire, passant de brillant a apagat. També es detalla el procés de la reacció del sodi amb aigua freda que produeix hidrogen i precisions sobre la flotació del sodi degut a la seva baixa densitat. Les característiques presents se solen comprovar en els laboratoris.

  • 00:20:00 - 00:25:00

    La reacció dels metalls amb vapor es combina amb la reacció amb aigua freda per introduir una distinció: els metalls més reactius reaccionen amb aigua freda formant hidròxids, mentre que els menys reactius, com el magnesi, reaccionen amb vapor per formar òxids. Es ressalta que els metalls per sota de l'hidrogen no reaccionen amb l’aigua. Aquesta secció juga un paper clau en l’estudi general de les reaccions químiques de metalls.

  • 00:25:00 - 00:30:00

    La reacció dels metalls amb àcids es destaca pel fet de formar hidrogen i compostos metàl·lics. S'explica la reactivitat comparativa entre diversos metalls com el magnesi que mostra més bombolles en comparació amb el zinc degut a la seva major reactivitat. Els experiments amb metalls com l’or que no reaccionen es relacionen amb la seva posició per sota de l’hidrogen en la sèrie de reactivitat.

  • 00:30:00 - 00:35:00

    S'explica el tipus de reaccions de desplaçament, detallant com un metall més reactiu pot desplaçar un menys reactiu del seu compost. Un exemple donat és la reacció entre zinc i sulfat de coure on el zinc desplaça el coure formant subproductes amb distincions visuals com el canvi de color de blau a incolor. També es ressalten les observacions experimentals d’aquests canvis.

  • 00:35:00 - 00:40:00

    El capítol tracta la oxidació dels metalls o la corrosió, amb un enfocament específic en l’òxid ferrós o òxid hidròxid de ferro que s’observa en la ràpida oxidació en presència d’aigua i oxigen. S’introdueixen els mètodes de prevenció com la galvanització i la protecció sacrificial que protegeixen els objectes metàl·lics de la trituració i corrosió per agents atmosfèrics.

  • 00:40:00 - 00:47:03

    Finalment, es detallen diferents mètodes per prevenir la corrosió dels metalls, com la galvanització, la qual consisteix en recobrir el ferro amb zinc per evitar l'oxidació, i la protecció sacrificial on un metall més reactiu com el zinc es consumeix abans que el ferro. També s'inclou electroplacatge, que usa corrent elèctric per recobrir els metalls amb diversos elements com la plata.

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Mind Map

Video Q&A

  • Quina estructura tenen els metalls?

    Els metalls tenen una estructura tridimensional formada per ions positius en files regulars rodejats per electrons delocalitzats.

  • Per què els metalls condueixen l'electricitat?

    Els metalls condueixen l'electricitat gràcies als electrons delocalitzats que es mouen lliurement.

  • Quines són les propietats físiques comunes als metalls?

    Tots els metalls condueixen l'electricitat, són maleables, ductils i brillants.

  • Què és la sèrie de reactivitat química?

    És una classificació dels metalls segons la seva reactivitat creixent, utilitzada per predir les seves reaccions.

  • Com reaccionen els metalls amb l'aigua?

    Els metalls reactius com el sodi reaccionen amb l'aigua freda per formar hidròxid mèssia i gas hidrogen.

  • Què s'observa quan el sodi reacciona amb aigua?

    El sodi flota, es mou per la superfície, produeix bombolles de gas i pot incendiar-se.

  • Quins metalls no reaccionen amb els àcids?

    Els metalls menys reactius com el coure no reaccionen amb els àcids.

  • Com es pot prevenir la corrosió del ferro?

    Mitjançant pintures, lubrificant amb oli, recobriment amb plàstic, galvanitzat i protecció sacrificial.

  • Quina diferència hi ha entre la reacció dels metalls amb aigua freda i amb vapor?

    Els metalls que reaccionen amb aigua freda formen hidròxids, mentre que amb vapor formen òxids.

  • Què és l'òxid de ferro(III) hidratar?

    L'òxid de ferro(III) hidratar és el que coneixem com a rovell del ferro.

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  • 00:00:01
    okay hello this is chapter 17
  • 00:00:03
    and now we're talking about metals so
  • 00:00:05
    we'll be discussing
  • 00:00:06
    physical and chemical properties of
  • 00:00:09
    metals in order to know that
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    we have to remind ourselves about the
  • 00:00:13
    structure of methods so we've done this
  • 00:00:15
    before
  • 00:00:16
    but you should remember that when he's
  • 00:00:18
    out when you're asked to
  • 00:00:20
    explain structure of metals you should
  • 00:00:23
    remember to say that metals have a giant
  • 00:00:26
    three-dimensional structure in which
  • 00:00:29
    regular rows of positive ions are
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    surrounded by
  • 00:00:32
    a sea of three moving electrons so we
  • 00:00:35
    said metals basically are solid
  • 00:00:37
    so they are made up of regular rows of
  • 00:00:40
    something now regular rows of what since
  • 00:00:43
    the metals
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    each atom has one or two or three
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    electrons in its outermost shell because
  • 00:00:49
    we said metals are basically
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    in group one group two group three and
  • 00:00:53
    everything in between
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    so each atom has one or two or three
  • 00:00:58
    electrons in its outermost shell that it
  • 00:01:00
    really doesn't want
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    so these the outermost electrons are
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    sort of floating around the atom
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    so the atom is no longer a neutral atom
  • 00:01:09
    it is now
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    a positive eye so these are arranged in
  • 00:01:13
    regular rows close
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    packed like any other solid but they are
  • 00:01:17
    also surrounded by
  • 00:01:19
    a sea of delocalized electrons or free
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    moving electrons
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    remember that sometimes you will be
  • 00:01:26
    required to draw
  • 00:01:28
    this kind of diagram to show the
  • 00:01:30
    structure of
  • 00:01:32
    methods okay so
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    this is a typical question that you
  • 00:01:37
    could have about structure of metals so
  • 00:01:39
    a question could say
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    a student draws this label diagram show
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    the particles in magnesium metal
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    he makes two mistakes in this diagram
  • 00:01:48
    state the two corrections he should make
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    to his label line so what's wrong with
  • 00:01:52
    this diagram
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    this is a diagram of what of magnesium
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    metal
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    now metals we just said are what they
  • 00:01:59
    are regular rules of
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    positive ions not positive and negative
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    positive negative positive negative
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    and then they are surrounded by a sea of
  • 00:02:07
    delocalized
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    what delocalized electrons so the two
  • 00:02:13
    mistakes in this diagram is that
  • 00:02:15
    first of all the ions should be positive
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    not positive and negative
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    and the it is surrounded by delocalized
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    electrons not protons
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    if we're as physical properties of all
  • 00:02:29
    metals you should remember
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    all metals conduct electricity all
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    metals are malleable and that time
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    all metals are shiny these are
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    properties of all metals there are no
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    exceptions
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    so all metals conduct electricity and if
  • 00:02:43
    we say
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    why they conduct electricity that is due
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    to presence of three moving electrons or
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    presence of the delocalized
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    electrons that are free to move
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    all metals are malleable and doctyle do
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    you remember what
  • 00:02:58
    is meant by malleable end of kind we
  • 00:03:01
    said malleable means
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    we can spread them into sheets like your
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    aluminium foil that we have at home
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    end of tile means they can be pulled
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    into wires like the coupled wires that
  • 00:03:13
    we have at home
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    so all metals are malleable and ductile
  • 00:03:18
    why is that
  • 00:03:19
    because the layers of positive ions that
  • 00:03:22
    are present in the metals can slide
  • 00:03:24
    over each other when heated or hammered
  • 00:03:28
    and of course all metals are shiny and
  • 00:03:30
    if we're asked about the appearance of
  • 00:03:32
    the metals we usually say they are
  • 00:03:35
    silvery appearance or silvery color
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    this is another typical question you
  • 00:03:42
    could be asked explain
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    why magnesium metal is malleable and a
  • 00:03:46
    good conductor of
  • 00:03:48
    electricity so we said it is what it's a
  • 00:03:50
    good conductor electricity because it
  • 00:03:52
    has
  • 00:03:53
    three moving electrons remember
  • 00:03:56
    the only one that we say free moving
  • 00:03:58
    ions is if i'm talking about an ionic
  • 00:04:01
    compound but this here is a metal so it
  • 00:04:04
    has
  • 00:04:04
    free moving electrons now we said
  • 00:04:07
    methods are malleable because
  • 00:04:09
    layers of positive ions slide over each
  • 00:04:11
    other when heated or hammered
  • 00:04:14
    okay so that was the physical properties
  • 00:04:16
    of metals now if we talk about the
  • 00:04:18
    chemical properties of metals we need to
  • 00:04:21
    talk about
  • 00:04:22
    chemical reactivity series so the
  • 00:04:24
    activity series is
  • 00:04:26
    just an arrangement of metals showing
  • 00:04:29
    which one is more reactive than which
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    but even without knowing or memorizing
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    the chemical reactivity series
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    you can deduce this from the periodic
  • 00:04:40
    table so just looking at the periodic
  • 00:04:42
    table you know
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    that everything in group 1 is more
  • 00:04:45
    reactive than group 2
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    and group 2 is more reactive than group
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    3 and group 3 is more reactive than
  • 00:04:52
    transition models so and within the same
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    group the one below is more reactive
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    than the one above
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    so if i say in group one potassium is
  • 00:05:02
    more reactive than sodium so we say
  • 00:05:04
    k and then na in group two we have
  • 00:05:08
    calcium more reactive than magnesium
  • 00:05:10
    because calcium is below mechanism in
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    the
  • 00:05:13
    periodic table then we say calcium and
  • 00:05:15
    then magnesium
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    and then group three has aluminium now
  • 00:05:19
    we include in the chemical reactivity
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    series we include
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    carbon and carbon monoxide because we
  • 00:05:25
    are going to compare the reactivity at
  • 00:05:27
    some point
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    later when we discuss it and then we go
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    into
  • 00:05:32
    the transition methods which is more
  • 00:05:34
    reactive than which in the transition
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    methods
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    zinc is more reactive than iron more
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    reactive than tin
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    remember that the chemical reactivity
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    series includes the metals that
  • 00:05:43
    are normally used in reactions so
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    some of the the metals in the periodic
  • 00:05:49
    table are not
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    usually used in reactions but the
  • 00:05:53
    chemical reactivity series arranges the
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    reactivity of the ones that we
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    normally discuss and then we put
  • 00:06:00
    hydrogen but
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    also because we're going to compare the
  • 00:06:03
    reactivity of metals to hydrogen at some
  • 00:06:06
    point and then below hydrogen we have
  • 00:06:08
    the metals that are not very reactive
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    so we have copper silver and gold these
  • 00:06:14
    are
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    below hydrogen in the reactivity series
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    so
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    this is the chemical reactivity series
  • 00:06:21
    cana canada
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    zinc iron tin and then copper silver
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    gold
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    if you don't memorize it check in the
  • 00:06:29
    periodic table as i told you
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    okay then we talk about the different
  • 00:06:40
    reactions of methods this is what we
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    mean by chemical properties of matter so
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    first of all
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    reaction of metals with oxygen so if i
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    have a gas
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    jar like the one in the diagram and i
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    have a gas jar
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    spoon and i put the metal in the spoon
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    lower it
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    into the gas jar light it allowed to
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    burn
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    in oxygen any metal will react with
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    oxygen to form
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    its oxide so sodium from sodium oxide
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    magnesium forms magnesium oxide and of
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    course we said
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    the reactivity depends on the
  • 00:07:16
    position in the group the one below in
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    the group
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    is more reactive than the one above you
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    have to know
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    that when we burn magnesium in air or
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    magnesium and oxygen
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    first of all what does it give you it
  • 00:07:29
    gives magnesium oxide
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    now what are the observations when i do
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    this kind of reaction
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    remember that the observation is when
  • 00:07:39
    magnesium burns
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    it burns with a bright flame or a white
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    flame and then it forms what it forms
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    magnesium oxide you should know that
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    magnesium oxide is
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    a white solid or white
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    ash okay um
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    you should also remember when we talked
  • 00:07:59
    about acids and bases we said that
  • 00:08:01
    oxides of
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    metals are usually basic that means if
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    you dissolve them in water they form an
  • 00:08:07
    alkaline solution that contains
  • 00:08:09
    hydroxide
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    ions but we also said that some metals
  • 00:08:13
    have
  • 00:08:14
    amphoteric oxide you remember the mean
  • 00:08:16
    of amphoteric
  • 00:08:17
    we said amphoteric oxide is one that can
  • 00:08:20
    act
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    both as an acid so it will react with
  • 00:08:23
    the base
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    or as a base so it will react with acid
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    and remember from the chapter in acids
  • 00:08:30
    and business we said which ones form
  • 00:08:32
    amphoteric oxides
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    aluminium zinc and blood form amphoteric
  • 00:08:37
    oxide so aluminum brings in oxygen to
  • 00:08:39
    the aluminium oxide
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    now this aluminum oxide can react with
  • 00:08:43
    acid
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    so in this case it's acting as a base
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    and that forms aluminium chloride plus
  • 00:08:48
    water
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    so it still forms a salt plus water
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    or it can act as an acid so it reacts
  • 00:08:55
    with a base like sodium hydroxide in
  • 00:08:57
    that case the salt is something called
  • 00:09:00
    sodium aluminate plus water
  • 00:09:05
    this is another question that you might
  • 00:09:06
    have so you could be asked
  • 00:09:09
    this question a student uses this
  • 00:09:11
    apparatus to find the mass of magnesium
  • 00:09:13
    oxide
  • 00:09:14
    that forms when a strip of magnesium
  • 00:09:16
    ribbon is burned in air
  • 00:09:18
    so usually this kind of experiments we
  • 00:09:20
    put the metal inside the crucible
  • 00:09:22
    and we cover it with a lid and we heat
  • 00:09:25
    it so the metal turns it
  • 00:09:27
    into its oxide and then i can wait or i
  • 00:09:30
    weigh the crucible and bleed at the
  • 00:09:31
    beginning and then
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    wait at the end and things like that
  • 00:09:36
    now the first question that you have
  • 00:09:37
    here says describe the appearance of the
  • 00:09:39
    freshly cleaned
  • 00:09:41
    magnesium ribbon and the appearance of
  • 00:09:43
    the magnesium oxide that forms
  • 00:09:45
    magnesium ribbon is a metal we said what
  • 00:09:48
    is the appearance of a metal
  • 00:09:51
    the appearance of a metal is silvery
  • 00:09:53
    okay what was magnesium oxide what was
  • 00:09:56
    the appearance of magnesium oxide
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    you have to remember it's a white solid
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    or white
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    ash explain why the student lifts the
  • 00:10:04
    lid and quickly replaces it several
  • 00:10:06
    times during the experiment
  • 00:10:08
    so when we do this kind of experiment
  • 00:10:10
    first of all i have to cover it i cannot
  • 00:10:12
    leave it open to the air
  • 00:10:13
    and then after some time i need to
  • 00:10:16
    remove the lid
  • 00:10:17
    open the lid and then close it again
  • 00:10:18
    open the lid and close it again
  • 00:10:20
    so what am i doing why why am i doing
  • 00:10:23
    this
  • 00:10:23
    i i lift the lid from time to time
  • 00:10:26
    remember that the magnesium is trying to
  • 00:10:28
    react with what
  • 00:10:30
    it's trying to react with oxygen so at
  • 00:10:32
    some point i don't want it to run out of
  • 00:10:34
    oxygen so i open the lid to allow more
  • 00:10:37
    oxygen to react to the magnesium
  • 00:10:39
    now why do i have to cover it can't i
  • 00:10:41
    just leave it open
  • 00:10:42
    no because we said what is formed is
  • 00:10:44
    magnesium oxide
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    and the magnesium oxide is white ash
  • 00:10:49
    that can
  • 00:10:50
    escape from the crucible so this is to
  • 00:10:52
    prevent loss of the product
  • 00:10:54
    from the crystal this is another
  • 00:10:58
    possible question that you might be
  • 00:10:59
    asked
  • 00:11:00
    lithium is stored in oil to prevent it
  • 00:11:02
    from coming into contact with air and
  • 00:11:04
    water remember this
  • 00:11:06
    that metals in group 1 are very reactive
  • 00:11:11
    when they are exposed to air and
  • 00:11:15
    or water they react very quickly so when
  • 00:11:17
    i store them
  • 00:11:18
    they have to be stored under oil so
  • 00:11:20
    things like lithium and sodium and
  • 00:11:23
    potassium
  • 00:11:24
    if we store them in the lab they have to
  • 00:11:25
    be stored under
  • 00:11:27
    oil this is to prevent them from
  • 00:11:29
    reacting with the
  • 00:11:31
    oxygen and water vapor there so the
  • 00:11:33
    question says when a piece of lithium is
  • 00:11:35
    removed from the oil dried and cut
  • 00:11:38
    the exposed surface so remember that
  • 00:11:42
    the x i cut the lithium this is a method
  • 00:11:45
    in group one and you
  • 00:11:46
    remember that methods in group one are
  • 00:11:48
    soft metals so you can cut them with a
  • 00:11:51
    knife
  • 00:11:52
    now once you cut them the the
  • 00:11:55
    surface of the metal is just like any
  • 00:11:58
    surface of a metal so that is shiny but
  • 00:12:00
    if i leave it exposed to the air what
  • 00:12:03
    happens
  • 00:12:05
    it will react with the oxygen water
  • 00:12:07
    vapor in the air and it will change from
  • 00:12:09
    shiny to double okay it will not form
  • 00:12:13
    bubbles because it's not reacting with
  • 00:12:15
    something to be the gas
  • 00:12:16
    it will not burst into flames this is
  • 00:12:19
    not
  • 00:12:20
    uh this is not cesium or
  • 00:12:23
    potassium remember that lithium is at
  • 00:12:25
    the the top of
  • 00:12:27
    group 1 so it is less reactive than
  • 00:12:30
    seasonal potassium since you might burst
  • 00:12:32
    into flame but lithium will not
  • 00:12:34
    does not change that's not a correct
  • 00:12:36
    answer so your answer is changes from
  • 00:12:38
    shiny
  • 00:12:39
    to that okay
  • 00:12:42
    now let's try talking about reaction
  • 00:12:45
    with
  • 00:12:46
    cold water so here we're talking about
  • 00:12:48
    reaction of sodium with cold water
  • 00:12:51
    if you put a piece of sodium it has to
  • 00:12:54
    be actually a very small piece of sodium
  • 00:12:56
    into a beaker containing water what
  • 00:12:59
    happens
  • 00:13:00
    first of all if i look at the reaction
  • 00:13:02
    i'm going to say that sodium is a
  • 00:13:03
    reactive metal so it reacts with cold
  • 00:13:06
    water and i'm going to tell you that
  • 00:13:09
    any metal that reacts with cold water
  • 00:13:12
    gives
  • 00:13:13
    the hydroxide plus hydrogen gas so
  • 00:13:16
    sodium in water will give sodium
  • 00:13:18
    hydroxide plus hydrogen
  • 00:13:21
    gas now what do we see when we put this
  • 00:13:23
    piece of sodium
  • 00:13:25
    in the water first of all sodium is in
  • 00:13:27
    group one
  • 00:13:28
    it it has low density so it floats
  • 00:13:32
    on the surface of the water now when it
  • 00:13:35
    floats it is
  • 00:13:36
    reacting with the water and giving out
  • 00:13:38
    bubbles of hydrogen gas
  • 00:13:40
    so these bubbles of hydrogen gas will
  • 00:13:42
    keep pushing the sodium around on the
  • 00:13:44
    surface of the water so we say that the
  • 00:13:46
    sodium floats
  • 00:13:48
    darts darts means moves around on the
  • 00:13:50
    surface of the water
  • 00:13:52
    and then it melts or disappears because
  • 00:13:54
    it is going to react and it will become
  • 00:13:57
    smaller until it disappears
  • 00:13:59
    also the bubbles of gas that i'm giving
  • 00:14:01
    out are
  • 00:14:02
    hydrogen gas so you you will see
  • 00:14:05
    vigorous
  • 00:14:06
    fizzing or bubbles of gases are coming
  • 00:14:09
    out very
  • 00:14:10
    quickly now the gases is coming out is
  • 00:14:13
    hydrogen gas and hydrogen gas
  • 00:14:15
    is flammable so the bubbles of hydrogen
  • 00:14:17
    gas
  • 00:14:18
    may catch fire if we want a
  • 00:14:21
    fourth observation remember that these
  • 00:14:23
    are the three most important
  • 00:14:24
    observations and he will ask you
  • 00:14:27
    what are the observations when sodium
  • 00:14:29
    react with cold water
  • 00:14:31
    a fourth observation would be the fact
  • 00:14:33
    that one because it gives sodium
  • 00:14:35
    hydroxide
  • 00:14:36
    as a product then the solution is
  • 00:14:39
    alkaline and that means if i put litmus
  • 00:14:42
    paper what happens
  • 00:14:44
    the solution turns litmus paper
  • 00:14:47
    to blue because the solution is alkaline
  • 00:14:52
    okay you have to know the observations
  • 00:14:55
    when we put sodium in cold water
  • 00:14:57
    so this is a typical question an example
  • 00:15:00
    of a question would be
  • 00:15:01
    a teacher investigates the reaction
  • 00:15:03
    between sodium and water the teacher
  • 00:15:05
    fills a trough of water
  • 00:15:07
    she adds a few drops of litmus solution
  • 00:15:09
    to the water and then adds
  • 00:15:10
    a piece of sodium so she's doing the
  • 00:15:13
    experiment that we just talked about
  • 00:15:14
    the sodium floats on the water yes we
  • 00:15:17
    said that
  • 00:15:18
    it reacts with the water and produces
  • 00:15:20
    bubbles of hydrogen gas
  • 00:15:21
    yes that's correct now he's asking you
  • 00:15:23
    to state two
  • 00:15:25
    other observations that are made so what
  • 00:15:27
    were the
  • 00:15:28
    other two observations he has already
  • 00:15:30
    said floats
  • 00:15:32
    he has already said bubbles or fizzing
  • 00:15:35
    so you can't say
  • 00:15:36
    fizzing so you can say the sodium darts
  • 00:15:39
    and
  • 00:15:40
    melts and the litmus solution because he
  • 00:15:43
    says that he has
  • 00:15:44
    litmus solution in the water the litmus
  • 00:15:46
    solution turns
  • 00:15:48
    blue okay this is another typical
  • 00:15:51
    question that you may be asked to
  • 00:15:52
    balance the equation for the reaction
  • 00:15:54
    between sodium and water
  • 00:15:56
    include state symbols what is the state
  • 00:15:59
    symbol for sodium
  • 00:16:01
    sodium is a metal so it's solid what was
  • 00:16:03
    the state symbol for water
  • 00:16:05
    we said water is always a liquid sodium
  • 00:16:08
    hydroxide is something that dissolves in
  • 00:16:10
    the water so that is
  • 00:16:12
    aqueous and hydrogen is a gas and then
  • 00:16:16
    you need to balance
  • 00:16:17
    can you understand how to balance you
  • 00:16:19
    should know how to balance so one sodium
  • 00:16:21
    before the arrow one sodium after the
  • 00:16:23
    other two hydrogens before the arrow
  • 00:16:25
    three hydrogens after the other so that
  • 00:16:28
    means that i need to put
  • 00:16:29
    a two in front of the water and the two
  • 00:16:32
    in front of the
  • 00:16:33
    sodium hydroxide that's i that makes it
  • 00:16:36
    four hydrogens
  • 00:16:38
    but that has ruined the sodium so the
  • 00:16:40
    sodium
  • 00:16:41
    needs a two in front of it now
  • 00:16:43
    everything is balanced
  • 00:16:46
    remember do not leave an equation
  • 00:16:48
    without balancing even if he doesn't
  • 00:16:50
    tell you to balance
  • 00:16:51
    lithium and potassium react in a similar
  • 00:16:53
    way to sodium when added to water
  • 00:16:56
    state why they have a similar reaction
  • 00:16:58
    in terms of electronic configurations of
  • 00:17:01
    their atoms
  • 00:17:02
    so what is common between lithium
  • 00:17:04
    potassium and sodium that makes them
  • 00:17:06
    react in a similar way
  • 00:17:08
    in terms of electronic configuration
  • 00:17:10
    electronic configuration means
  • 00:17:12
    in terms of the arrangement of the
  • 00:17:13
    electrons so the fact that they have
  • 00:17:16
    all of them have one electron and outer
  • 00:17:18
    shell because they are all in group one
  • 00:17:21
    so they all react in the same way now
  • 00:17:24
    place the elements lithium potassium and
  • 00:17:26
    sodium in order of
  • 00:17:28
    reactivity do you remember the activity
  • 00:17:31
    if you don't remember the reactivity
  • 00:17:33
    series you can just check the periodic
  • 00:17:35
    table
  • 00:17:35
    you will find that potassium is in the
  • 00:17:38
    is at the bottom
  • 00:17:39
    sodium lithium and we said the one at
  • 00:17:41
    the bottom
  • 00:17:42
    is the most reactive so potassium sodium
  • 00:17:45
    lithium that is the arrangement of the
  • 00:17:47
    reactant
  • 00:17:50
    okay another possible question the table
  • 00:17:53
    below lists some statements about the
  • 00:17:55
    reaction of caesium with cold water
  • 00:17:57
    compared to the reaction of lithium with
  • 00:17:59
    cold water
  • 00:18:01
    so he's comparing lithium to cesium
  • 00:18:03
    remember we said where is caesium
  • 00:18:05
    caesium is at the bottom of the of the
  • 00:18:08
    group one
  • 00:18:08
    in the periodic table so which one would
  • 00:18:11
    be more reactive the lithium or the
  • 00:18:13
    season
  • 00:18:14
    of course cesium is at the bottom of the
  • 00:18:16
    periodic of the
  • 00:18:17
    uh group one in the periodic table so
  • 00:18:20
    cesium should be more reactive than
  • 00:18:23
    lithium so he's saying i'm comparing
  • 00:18:26
    caesium to the reaction of lithium
  • 00:18:30
    the first choice is the reaction with
  • 00:18:32
    caesium is more
  • 00:18:33
    vigorous is that correct yes of course
  • 00:18:36
    it is correct
  • 00:18:37
    because caesium is more reactive since
  • 00:18:39
    it is at the bottom of the
  • 00:18:41
    table one the first
  • 00:18:45
    group the reaction with cesium produces
  • 00:18:47
    a different
  • 00:18:48
    gas is that correct no all of them all
  • 00:18:51
    the metals will react with cold water to
  • 00:18:54
    form
  • 00:18:55
    hydrogen gas the reaction with
  • 00:18:59
    so uh cesium produces an acidic solution
  • 00:19:01
    no
  • 00:19:02
    we said what is formed when you act with
  • 00:19:04
    cold water is caesium hydroxide
  • 00:19:07
    and that's alkali not acidity the
  • 00:19:09
    reaction with sediment produces a
  • 00:19:10
    different compound
  • 00:19:13
    yes of course because cesium will give
  • 00:19:15
    you caesium hydroxide why lithium will
  • 00:19:18
    give lithium hydroxyl
  • 00:19:20
    the reaction of caesium is endothermic
  • 00:19:22
    do you remember what we mean by
  • 00:19:23
    endothermic
  • 00:19:25
    endothermic means you need to heat it in
  • 00:19:27
    order to react it takes in heat
  • 00:19:30
    or is it exothermic it gives out heat no
  • 00:19:33
    reaction of season with water is not
  • 00:19:35
    endothermic it is
  • 00:19:36
    exothermic now the next question says
  • 00:19:39
    write a chemical equation for the
  • 00:19:40
    reaction of season with
  • 00:19:42
    water again we said season with water
  • 00:19:45
    because this is
  • 00:19:46
    cold water it will form caesium
  • 00:19:48
    hydroxide plus
  • 00:19:50
    hydrogen and then you balance in this
  • 00:19:53
    way
  • 00:19:54
    okay reaction of calcium with
  • 00:19:57
    cold water so calcium if it reacts with
  • 00:20:00
    cold water it will give exactly the same
  • 00:20:02
    it will give calcium hydroxide
  • 00:20:05
    plus hydrogen so what am i going to see
  • 00:20:08
    now in this case
  • 00:20:10
    calcium is in group 2 so it is heavier
  • 00:20:13
    than water it is denser than water so it
  • 00:20:15
    will sink
  • 00:20:16
    so my first observation is that calcium
  • 00:20:19
    will sink not float like sodium
  • 00:20:22
    but it will still give hydrogen gas so i
  • 00:20:24
    will still have strong
  • 00:20:26
    fizzing and the solution becomes milky
  • 00:20:29
    because the calcium hydroxide that is
  • 00:20:31
    formed is not very soluble in water
  • 00:20:34
    so slowly and forming some sort of white
  • 00:20:37
    precipitate so that makes the solution
  • 00:20:40
    milky or cloudy
  • 00:20:43
    now when we go to the less reactive
  • 00:20:45
    metals because magnesium is less
  • 00:20:47
    reactive than the
  • 00:20:48
    calcium it will not react with cold
  • 00:20:51
    water easily
  • 00:20:53
    if i put it in cold water the reaction
  • 00:20:55
    is too slow
  • 00:20:57
    it will still give magnesium hydroxide
  • 00:20:59
    if it's reacting with cold water but it
  • 00:21:00
    is very
  • 00:21:01
    slow now if i want the reaction to be
  • 00:21:04
    quick i have to heat it that means the
  • 00:21:06
    water
  • 00:21:07
    has to be in the form of steam so i heat
  • 00:21:10
    the water soaked cotton wall the
  • 00:21:12
    water vapor or the steam passes
  • 00:21:15
    over the magnesium ribbon that has been
  • 00:21:19
    heated
  • 00:21:20
    again remember that the magnesium when
  • 00:21:22
    it is heated it burns with a bright
  • 00:21:24
    flame and then what is formed magnesium
  • 00:21:28
    oxide not hydroxide
  • 00:21:31
    so a metal that reacts with cold water
  • 00:21:34
    gives the hydroxide
  • 00:21:36
    a metal that reacts with steam will give
  • 00:21:39
    the oxide magnesium oxide plus hydrogen
  • 00:21:42
    so again my observations would be
  • 00:21:45
    that magnesium burns with a bright flame
  • 00:21:47
    magnesium oxide is a white solid so a
  • 00:21:50
    white solid is formed
  • 00:21:51
    and hydrogen gas is formed which burns
  • 00:21:54
    or we have bubbles of
  • 00:21:55
    hydrogen when zinc reacts with steam
  • 00:21:59
    again zinc is less reactive so it does
  • 00:22:02
    not react with cold water it reacts with
  • 00:22:05
    steam and we said when a metal reacts
  • 00:22:07
    with steam it forms
  • 00:22:09
    the oxide so this forms zinc oxide
  • 00:22:12
    plus hydrogen so any metal that will
  • 00:22:15
    react
  • 00:22:15
    with cold water forms hydroxide so this
  • 00:22:19
    is the ones in group one and the bottom
  • 00:22:21
    of group two
  • 00:22:23
    react with cold water to give hydroxide
  • 00:22:27
    the less reactive metals like group 3
  • 00:22:31
    and the transition metals they react
  • 00:22:34
    with steam
  • 00:22:36
    but when they react with steam they form
  • 00:22:39
    the oxide
  • 00:22:40
    not the hydroxide okay
  • 00:22:44
    remember that metals below
  • 00:22:47
    hydrogen in the peri in the
  • 00:22:49
    electrochemical series
  • 00:22:50
    metals that are less reactive than
  • 00:22:52
    hydrogen will not react with water at
  • 00:22:55
    all
  • 00:22:55
    so if i put copper in water it does not
  • 00:22:58
    react
  • 00:22:58
    at all okay metals with acid
  • 00:23:03
    so metal with acid gives
  • 00:23:06
    hydrogen gas plus a salt depending on
  • 00:23:09
    which metal
  • 00:23:10
    so something like magnesium plus hcl
  • 00:23:12
    will give hydrogen gas and anything that
  • 00:23:14
    gives a gas
  • 00:23:15
    gives bubbles of gas now the more
  • 00:23:17
    reactive the metal the more the bubbles
  • 00:23:20
    so for example magnesium is more
  • 00:23:22
    reactive than zinc so the bubbles that i
  • 00:23:24
    see
  • 00:23:24
    when i react the acid with magnesium is
  • 00:23:27
    much more than the ones
  • 00:23:29
    formed um when we react it with
  • 00:23:32
    zinc now if i put copper in acid
  • 00:23:36
    no reaction no bubbles at all again
  • 00:23:39
    remember copper is below hydrogen in the
  • 00:23:42
    reactivity series so it does not react
  • 00:23:45
    with water
  • 00:23:46
    it does not react with acids you can't
  • 00:23:49
    say copper plus an acid
  • 00:23:52
    so a typical question give two
  • 00:23:54
    observations that are made when a piece
  • 00:23:56
    of magnesium ribbon is added to
  • 00:23:58
    acidic solution so you put magnesium in
  • 00:24:00
    acid
  • 00:24:01
    what two observations would you see
  • 00:24:04
    again
  • 00:24:04
    we said if i put magnesium in acid like
  • 00:24:07
    hcl for example it gives
  • 00:24:09
    a hydrogen gas right so what i see would
  • 00:24:12
    be bubbles of glass now what's the other
  • 00:24:14
    observation
  • 00:24:15
    the other observation is that the
  • 00:24:17
    magnesium as a solid that i put into the
  • 00:24:19
    acid eventually it will start to
  • 00:24:21
    dissolve or it will
  • 00:24:23
    disappear or it will become smaller
  • 00:24:26
    okay so we say the magnesium solid
  • 00:24:28
    dissolves or
  • 00:24:31
    disappears or becomes
  • 00:24:36
    another possible question that you could
  • 00:24:38
    see would say something like this
  • 00:24:40
    magnesium is a reactive metal
  • 00:24:42
    its reactivity can be seen in its
  • 00:24:44
    reactions with oxygen dilute sulfuric
  • 00:24:46
    acid
  • 00:24:47
    and he gives you two reactions one with
  • 00:24:50
    oxygen to give magnesium oxide
  • 00:24:52
    and one with sulfuric acid to give
  • 00:24:54
    magnesium sulfate plus
  • 00:24:56
    hydrogen so the first question says in
  • 00:24:59
    reaction one some magnesium is ignited
  • 00:25:01
    and then placed in a jar of oxygen gas
  • 00:25:04
    state two observations that will be made
  • 00:25:06
    we said what are the observations that
  • 00:25:09
    we see
  • 00:25:10
    when we burn magnesium in oxygen
  • 00:25:13
    again we said the magnesium burns with a
  • 00:25:16
    bright flame
  • 00:25:17
    and a white solid is formed because
  • 00:25:20
    magnesium oxide is a white solid
  • 00:25:24
    the other question is a possible
  • 00:25:27
    question that you could have
  • 00:25:29
    in an experiment a student adds a piece
  • 00:25:31
    of zinc to some dilute hydrochloric acid
  • 00:25:33
    in a test tube so it has a piece of zinc
  • 00:25:36
    in diabetes
  • 00:25:38
    the student measures the temperature
  • 00:25:39
    before adding the zinc
  • 00:25:41
    after adding the zinc he stairs the
  • 00:25:43
    mixture measures the highest temperature
  • 00:25:45
    and then he wants to find out if there
  • 00:25:47
    is a relationship between the activity
  • 00:25:49
    of a metal and the temperature rise
  • 00:25:51
    so he repeats the experiment four times
  • 00:25:53
    using a different metal each time so
  • 00:25:55
    basically
  • 00:25:56
    he's putting different methods into the
  • 00:25:59
    acid
  • 00:25:59
    measuring the initial temperature and
  • 00:26:01
    the final temperature so he can
  • 00:26:03
    determine how much rise
  • 00:26:05
    in temperature there was okay
  • 00:26:08
    so state three factors that the student
  • 00:26:11
    should keep constants in each
  • 00:26:12
    experiment so what the what should he he
  • 00:26:15
    should be changing
  • 00:26:16
    only the type of metal
  • 00:26:20
    but he shouldn't be changing what he
  • 00:26:22
    shouldn't be changing the surface area
  • 00:26:23
    of the metal
  • 00:26:24
    the concentration of the acid the volume
  • 00:26:27
    of the acid remember the surface area of
  • 00:26:29
    the metal means i shouldn't use
  • 00:26:31
    uh one metal in the form of big pieces
  • 00:26:33
    and the other matter in the form of
  • 00:26:34
    powder for example they should be the
  • 00:26:36
    same
  • 00:26:37
    surface area and they should be the same
  • 00:26:39
    mass of the metal
  • 00:26:41
    so you can either say same surface area
  • 00:26:43
    of metal
  • 00:26:44
    say mass of metal and then the acid
  • 00:26:46
    should have the same volume the same
  • 00:26:48
    concentration
  • 00:26:50
    using information from the table state
  • 00:26:52
    the relationship between reactivity of a
  • 00:26:54
    metal and
  • 00:26:55
    temperature rise so what was the table
  • 00:26:57
    this was the table
  • 00:26:59
    so magnesium gold iron calcium
  • 00:27:03
    what type of reactivity or what is the
  • 00:27:06
    arrangement of reactivity of these
  • 00:27:08
    muscles you should realize that we said
  • 00:27:10
    calcium is more reactive than magnesium
  • 00:27:13
    and then this these are more reactive
  • 00:27:15
    than iron
  • 00:27:16
    and then gold was at the bottom of the
  • 00:27:18
    reactivity series and we said it's
  • 00:27:21
    not very reactive so when they put it in
  • 00:27:24
    acids they found that the more reactive
  • 00:27:27
    metal is the one that gives
  • 00:27:28
    higher temperature so remember that more
  • 00:27:32
    reactivity
  • 00:27:33
    is indicated by what is indicated by
  • 00:27:36
    more bubbles of gas or by more
  • 00:27:39
    rise in temperature so the more reactive
  • 00:27:42
    the metal the greater the temperature
  • 00:27:44
    rise
  • 00:27:45
    states why there is no temperature rise
  • 00:27:47
    when gold is added
  • 00:27:48
    since there is no temperature rise this
  • 00:27:50
    means that gold does not react with
  • 00:27:53
    the acid another typical question that
  • 00:27:56
    you could see would say the diagram
  • 00:27:58
    shows how a student attempts to prepare
  • 00:28:00
    some hydrogen gas
  • 00:28:02
    state why no hydrogen is produced look
  • 00:28:04
    at the
  • 00:28:05
    diagram and tell me why do you think he
  • 00:28:06
    didn't get any gas
  • 00:28:09
    if he didn't get any gas that is just
  • 00:28:11
    because
  • 00:28:12
    the silver did not react and why doesn't
  • 00:28:15
    it react
  • 00:28:16
    because it is below hydrogen in the
  • 00:28:18
    reactivity
  • 00:28:19
    series so he's reacting it with silver
  • 00:28:22
    remember that we said
  • 00:28:23
    anything below hydrogen in the
  • 00:28:25
    reactivity series
  • 00:28:26
    will not react with water
  • 00:28:30
    or acid so the what which metals do we
  • 00:28:33
    have below the reactivity series we have
  • 00:28:36
    copper silver gold and we also have
  • 00:28:39
    mercury at some
  • 00:28:40
    point so silver does not react with
  • 00:28:43
    acids because
  • 00:28:44
    it is below hydrogen or it is less
  • 00:28:46
    reactive than
  • 00:28:47
    hydrogen which of these pairs of
  • 00:28:49
    chemicals could be used to
  • 00:28:50
    safely prepare hydrogen
  • 00:28:54
    to prepare hydrogen that means they have
  • 00:28:56
    to react with the acid to form
  • 00:28:58
    hydrogen and i don't want it to be too
  • 00:29:00
    vigorous because he wants it safe
  • 00:29:03
    so the first option here a
  • 00:29:06
    says copper and acid remember that we
  • 00:29:08
    said both copper and gold
  • 00:29:11
    and silver are below hydrogen in the
  • 00:29:14
    electrochemical series
  • 00:29:16
    or the reactivity series so they will
  • 00:29:18
    not react with
  • 00:29:20
    acids or with water now that means i
  • 00:29:23
    have a choice between potassium and
  • 00:29:26
    zinc but potassium is in group 1 it is a
  • 00:29:30
    very reactive metal if i put it in
  • 00:29:32
    acid it will sort of explode or very
  • 00:29:36
    violent reaction zinc reacts
  • 00:29:39
    but it's not violent so that would be
  • 00:29:42
    our
  • 00:29:42
    choice okay
  • 00:29:46
    the other type of reactions that we have
  • 00:29:48
    are displacement reactions a
  • 00:29:50
    displacement reaction means
  • 00:29:52
    a more reactive metal will push the less
  • 00:29:55
    reactive metal out of its salt
  • 00:29:58
    so if i have zinc plus copper sulfate
  • 00:30:01
    if i have a reaction that means that
  • 00:30:04
    zinc is more reactive than coupling
  • 00:30:06
    if we do this for two metals
  • 00:30:09
    and they don't react that means that
  • 00:30:12
    zinc
  • 00:30:12
    is not or is less reactive than copper
  • 00:30:15
    so when i put zinc in copper sulfate it
  • 00:30:18
    will react
  • 00:30:19
    because zinc is more reactive than
  • 00:30:21
    copper what does it give me it gives me
  • 00:30:23
    zinc sulfate plus copper now can you see
  • 00:30:27
    the original color of copper sulfate you
  • 00:30:29
    should know that
  • 00:30:30
    the original color of copper sulfate
  • 00:30:31
    solution is blue
  • 00:30:34
    but zinc sulfate is colorless so
  • 00:30:38
    one observation that you would see is
  • 00:30:40
    that the fact that the blue color of
  • 00:30:41
    copper sulfate
  • 00:30:43
    changes to colorless also i started with
  • 00:30:46
    zinc solid and the zinc
  • 00:30:47
    reacted in the copper sulfate so at some
  • 00:30:50
    point the zinc will dissolve or
  • 00:30:52
    start to disappear or become smaller
  • 00:30:55
    and then we're forming what we're
  • 00:30:57
    forming copper copper metal you should
  • 00:30:59
    remember copper metal is
  • 00:31:01
    the red or reddish brown metal
  • 00:31:04
    so when it forms copper it forms a red
  • 00:31:06
    precipitate
  • 00:31:07
    in the test tube can you see that so
  • 00:31:10
    these are the observations when you put
  • 00:31:12
    zinc in copper sulfate now
  • 00:31:15
    another example of a displacement
  • 00:31:18
    reaction would be magnesium plus copper
  • 00:31:20
    carbonate magnesium is more reactive
  • 00:31:22
    than copper so it will displace it from
  • 00:31:24
    its soles
  • 00:31:25
    the copper carbonate is originally a
  • 00:31:28
    green color
  • 00:31:30
    when it changes into magnesium carbonate
  • 00:31:33
    it is now a compound
  • 00:31:34
    of group two compounds of group two have
  • 00:31:36
    no color
  • 00:31:37
    so the solution becomes colorless and i
  • 00:31:40
    will start to see a reddish precipitate
  • 00:31:43
    of
  • 00:31:43
    copper okay a typical question
  • 00:31:47
    let's take a look at what type of
  • 00:31:48
    question we have
  • 00:31:53
    so here he says in an experiment a piece
  • 00:31:55
    of zinc metal is placed in a beaker
  • 00:31:57
    containing copper sulfate so he was
  • 00:31:59
    talking about the ex he
  • 00:32:00
    here he's talking about the reaction
  • 00:32:02
    between zinc and capacitor fate
  • 00:32:04
    the reaction that occurs shows zinc is
  • 00:32:06
    more reactive than copper
  • 00:32:08
    state to observation so what are two
  • 00:32:10
    observations that i will see
  • 00:32:12
    when i put zinc in copper sulfate
  • 00:32:15
    we said the original color of copper
  • 00:32:17
    surface is what
  • 00:32:19
    blue so we said the blue solution turns
  • 00:32:22
    colorless
  • 00:32:23
    and the zinc metal begins to dissolve or
  • 00:32:26
    disappear
  • 00:32:27
    the diagram shows two ways in which
  • 00:32:29
    potassium can be converted into
  • 00:32:31
    potassium chloride
  • 00:32:33
    give the names of x y and z
  • 00:32:36
    so let's take a look at this flow chart
  • 00:32:38
    it starts with potassium
  • 00:32:41
    he heats it in gas x to form potassium
  • 00:32:45
    chloride
  • 00:32:46
    so which gas do i react with potassium
  • 00:32:50
    to form potassium chloride
  • 00:32:53
    i need okay
  • 00:32:56
    okay then he says he added water to
  • 00:32:59
    potassium
  • 00:33:00
    and he got a colorless solution of wine
  • 00:33:03
    what happens if i add
  • 00:33:04
    water to potassium we said potassium is
  • 00:33:07
    a reactive metal it reacts with cold
  • 00:33:09
    water
  • 00:33:10
    so what i form would be potassium
  • 00:33:12
    hydroxide
  • 00:33:15
    and then this potassium hydroxide he
  • 00:33:17
    wants to react it with an acid
  • 00:33:19
    to form potassium chloride which acid
  • 00:33:22
    should i
  • 00:33:22
    add to potassium hydroxide to form
  • 00:33:25
    potassium chloride
  • 00:33:28
    hydrochloric acid the acid that has
  • 00:33:31
    chlorine in it
  • 00:33:32
    and notice that the question said give
  • 00:33:35
    the names of these so i have to write
  • 00:33:38
    the names of these
  • 00:33:40
    you shouldn't write the formulas and if
  • 00:33:42
    you do decide to write formula please
  • 00:33:45
    write the correct
  • 00:33:46
    formula but if he says name give him
  • 00:33:48
    name when sodium is burned in iodine gas
  • 00:33:51
    sodium iodide is formed
  • 00:33:53
    write a chemical equation for the
  • 00:33:54
    reaction between sodium and
  • 00:33:56
    iodine so i'm going to write a chemical
  • 00:33:59
    reaction
  • 00:34:00
    sodium plus iv to give what it should
  • 00:34:03
    give sodium iodide sodium has a valency
  • 00:34:05
    of one and iodine has a valency of one
  • 00:34:07
    so i don't write it two
  • 00:34:09
    under any of them have i finished
  • 00:34:13
    no i have to balance the equation
  • 00:34:16
    even if he doesn't say balance a
  • 00:34:18
    chemical equation means it has to be
  • 00:34:20
    balanced
  • 00:34:20
    so you need a two to make the two
  • 00:34:22
    iodines
  • 00:34:24
    and a two henna to fix the surgery
  • 00:34:27
    okay the next thing we're talking about
  • 00:34:31
    is rusting of iron
  • 00:34:32
    remember that iron when you expose it
  • 00:34:36
    iron is originally silver in color so
  • 00:34:38
    this
  • 00:34:39
    nice clean chain on the right side is
  • 00:34:43
    a clean iron that is that hasn't trusted
  • 00:34:46
    but when you expose it to the atmosphere
  • 00:34:50
    it turns into reddish brown as we can
  • 00:34:54
    see
  • 00:34:55
    so this is called rust this reddish
  • 00:34:57
    brown cover
  • 00:34:58
    on the iron is called rust if we're
  • 00:35:01
    talking about iron we call it rust if
  • 00:35:03
    we're talking about any other metal we
  • 00:35:05
    call it
  • 00:35:06
    corrosion of eye of of the metal so
  • 00:35:09
    all metals corrode corrode means they
  • 00:35:11
    react with
  • 00:35:13
    water and oxygen in the air
  • 00:35:16
    but when we are talking about iron we
  • 00:35:18
    can say corrosion of iron or
  • 00:35:20
    rusting of iron we don't say rusting of
  • 00:35:22
    any other metal
  • 00:35:24
    now what do we need for the iron to
  • 00:35:27
    rust or for the iron to corrode we can
  • 00:35:30
    have an experiment like this in which we
  • 00:35:32
    have
  • 00:35:32
    males and we have them in different
  • 00:35:34
    things so when they put names in
  • 00:35:36
    distilled water
  • 00:35:38
    and you should remember that distilled
  • 00:35:39
    water means water that has
  • 00:35:41
    oxygen dissolved in it any normal water
  • 00:35:44
    that we have
  • 00:35:45
    has a little bit of oxygen dissolved in
  • 00:35:47
    it so when we put the nails in distilled
  • 00:35:50
    water the nails rust
  • 00:35:53
    distilled water contains both water and
  • 00:35:55
    oxygen
  • 00:35:56
    now if i put the nails in boiled
  • 00:35:59
    water now what is boiled water boiled
  • 00:36:01
    water is water
  • 00:36:02
    that i have boiled so all the oxygen
  • 00:36:05
    dissolved in it has escaped
  • 00:36:07
    when you boil the water they dissolve
  • 00:36:09
    the gases go out
  • 00:36:10
    so dissolve the oxygen has gone out it
  • 00:36:12
    doesn't have any dissolved oxygen and
  • 00:36:14
    i'm covering it with a layer of oil to
  • 00:36:16
    make sure that no more oxygen
  • 00:36:18
    dissolves in it now when we put the
  • 00:36:20
    nails in the boiled water that means i
  • 00:36:22
    don't have any oxygen
  • 00:36:24
    i find that the nails will not rust now
  • 00:36:27
    if i put the nails in another test tube
  • 00:36:29
    that contain
  • 00:36:30
    anhydrous calcium chloride you should
  • 00:36:32
    remember that anhydrous calcium chloride
  • 00:36:35
    is
  • 00:36:35
    something that absorbs water vapor from
  • 00:36:38
    the air
  • 00:36:39
    so basically this test tube has no water
  • 00:36:42
    and if i leave the nails in this test
  • 00:36:45
    tube
  • 00:36:46
    the nails will not rust
  • 00:36:49
    if we put the nails in sea water now
  • 00:36:52
    what is sea water sea water has
  • 00:36:54
    water and oxygen and soils so
  • 00:36:57
    i will find that in sea water in the
  • 00:36:59
    presence of salts or
  • 00:37:01
    sometimes in the presence of acid the
  • 00:37:03
    nails will
  • 00:37:04
    rust very quickly so it's
  • 00:37:08
    salt makes the nails rust quickly
  • 00:37:11
    so what does the iron basically need in
  • 00:37:14
    order to rust
  • 00:37:15
    the iron needs both water and oxygen
  • 00:37:18
    if you're missing any of them then the
  • 00:37:20
    nails do not trust
  • 00:37:22
    so the iron requires both water
  • 00:37:25
    and oxygen in order to rust now what is
  • 00:37:28
    rust
  • 00:37:28
    rusting means that the iron changes into
  • 00:37:32
    iron iii oxide or actually it is
  • 00:37:35
    hydrated
  • 00:37:37
    iron iii oxide which is the reddish
  • 00:37:40
    brown
  • 00:37:40
    flaky uh cover on the
  • 00:37:43
    on the iron so what is rust
  • 00:37:47
    it is hydrated iron iii oxide that means
  • 00:37:50
    the iron is changing to iron oxide and
  • 00:37:53
    that means that this
  • 00:37:55
    rusting or corrosion is actually an
  • 00:37:58
    oxidation process right
  • 00:38:01
    and then if we say what is the
  • 00:38:03
    appearance of rust rust is reddish brown
  • 00:38:05
    and flaky what do you mean by flaky
  • 00:38:08
    flaky means it can
  • 00:38:09
    peel off it can fall off so this piece
  • 00:38:12
    of nail if i leave it
  • 00:38:14
    for a long time the rust that forms on
  • 00:38:17
    it can
  • 00:38:18
    peel off and if the nails are left long
  • 00:38:21
    enough they will eventually just change
  • 00:38:23
    into
  • 00:38:24
    a red brown powder because all of the
  • 00:38:27
    rust
  • 00:38:27
    peels off okay so
  • 00:38:31
    what do we do to prevent trusting i
  • 00:38:33
    don't want my
  • 00:38:34
    iron objects to rust
  • 00:38:37
    so what should i do the first thing that
  • 00:38:40
    we normally do or the easiest thing that
  • 00:38:42
    we normally do
  • 00:38:43
    is painting so if i have railings these
  • 00:38:47
    are railings the ones that we
  • 00:38:49
    hold on when we go down the stairs or
  • 00:38:52
    gates iron gates or windows
  • 00:38:56
    the normal thing that we do is paint now
  • 00:38:59
    painting
  • 00:39:00
    what does painting do painting covers
  • 00:39:03
    the iron
  • 00:39:04
    so that it prevents it from reacting
  • 00:39:06
    with oxygen and water vapor in the air
  • 00:39:09
    but the problem with that is if the
  • 00:39:11
    layer of paint is peeled off
  • 00:39:13
    or scraped off that piece of iron or
  • 00:39:16
    that
  • 00:39:17
    part of the iron will again start to
  • 00:39:19
    rust
  • 00:39:20
    so it is something that has to be done a
  • 00:39:23
    lot
  • 00:39:23
    another method of preventing
  • 00:39:27
    rusting would be to coat with oil and
  • 00:39:29
    grease when do we use coating of oil and
  • 00:39:31
    grease we use it when we're talking
  • 00:39:33
    about machines
  • 00:39:34
    so if i have a machine in which i don't
  • 00:39:37
    want these pieces of iron
  • 00:39:38
    to rust or if there's a lot of friction
  • 00:39:41
    between them
  • 00:39:42
    i coat them with oil or grease
  • 00:39:47
    another method would be coating with
  • 00:39:49
    plastic now when do we use this
  • 00:39:51
    in your dishwasher the racks in the
  • 00:39:53
    dishwasher that you put your dishes on
  • 00:39:56
    these are pieces of iron that are
  • 00:39:59
    coated with plastic again why are we
  • 00:40:02
    coating it with plastic to prevent the
  • 00:40:04
    iron from
  • 00:40:05
    reacting with water and oxygen in the
  • 00:40:09
    air
  • 00:40:10
    the problem again is if the piece of
  • 00:40:12
    plastic
  • 00:40:13
    is scraped off or is removed
  • 00:40:17
    that exposed surface will again start to
  • 00:40:20
    rust
  • 00:40:22
    okay a better way of preventing
  • 00:40:25
    um rusting would be what we call
  • 00:40:28
    galvanizing galvanizing means
  • 00:40:31
    covering the iron with a layer of zinc
  • 00:40:34
    by dipping or spraying so these are
  • 00:40:37
    iron pipes for example or iron tubes of
  • 00:40:40
    some sort
  • 00:40:42
    i want to prevent it from
  • 00:40:46
    rusting so i can dip them into
  • 00:40:49
    liquid zinc so that container contains
  • 00:40:53
    zinc that is molten molten zinc
  • 00:40:57
    and i dip the iron into it or i can
  • 00:41:00
    spray it with
  • 00:41:02
    zinc the zinc covers the iron
  • 00:41:06
    this process is called galvanizing it
  • 00:41:09
    prevents rusting because
  • 00:41:11
    that outer layer of zinc is a metal that
  • 00:41:15
    is more reactive than iron so the zinc
  • 00:41:18
    will react and lose electrons and be
  • 00:41:22
    oxidized
  • 00:41:23
    instead of the iron and the good thing
  • 00:41:26
    about it
  • 00:41:27
    is even if part of this layer of zinc
  • 00:41:31
    is scraped off still the iron will not
  • 00:41:35
    rust so long as any part of it is still
  • 00:41:38
    touching the zinc
  • 00:41:40
    so so long as there is still some zinc
  • 00:41:42
    attached to the iron
  • 00:41:44
    it is the zinc that will be oxidized not
  • 00:41:47
    the iron
  • 00:41:48
    do we understand this so covering with a
  • 00:41:50
    layer of zinc by dipping your spray that
  • 00:41:52
    is called
  • 00:41:53
    galvanizing or galvanization
  • 00:41:57
    how does it work the zinc is more
  • 00:41:59
    reactive than iron
  • 00:42:00
    so it loses electrons and becomes
  • 00:42:02
    oxidized instead of the iron
  • 00:42:05
    and the advantage is even if a piece of
  • 00:42:08
    the zinc
  • 00:42:08
    is removed still so long as the iron is
  • 00:42:12
    touching
  • 00:42:12
    something it will not rust or it will
  • 00:42:16
    not corrode
  • 00:42:17
    okay another method is sacrificial
  • 00:42:19
    protection
  • 00:42:20
    now sacrificial protection is basically
  • 00:42:22
    the same idea but instead of
  • 00:42:25
    covering with a layer of zinc i just
  • 00:42:27
    attach
  • 00:42:28
    a block of a more reactive metal
  • 00:42:31
    to the steel or to iron for example
  • 00:42:35
    in ships the ship is made of iron i
  • 00:42:38
    don't want the ship
  • 00:42:39
    to corrode so i just put a zinc
  • 00:42:42
    bar attach it to
  • 00:42:45
    the side of the ship this presence of
  • 00:42:48
    the zinc bar attached to the side of the
  • 00:42:50
    ship
  • 00:42:51
    prevents the whole ship from rusting
  • 00:42:55
    this is because so long as the iron is
  • 00:42:58
    touching
  • 00:42:58
    some zinc the zinc will react instead of
  • 00:43:02
    the ions
  • 00:43:03
    since it is more reactive so it will
  • 00:43:05
    become oxidized and lose electrons
  • 00:43:07
    instead of the eye
  • 00:43:08
    so we can use a piece of zinc or we can
  • 00:43:11
    use a piece of magnesium for example
  • 00:43:13
    bolted to the side of the ship
  • 00:43:16
    another method of preventing corrosion
  • 00:43:19
    was the electroplating that we talked
  • 00:43:21
    about when we were
  • 00:43:23
    doing electrons so electroplating
  • 00:43:26
    is a reaction with
  • 00:43:30
    uh electric current using electric
  • 00:43:33
    current
  • 00:43:34
    so i attach a piece of i want to cover
  • 00:43:36
    my spoon for example
  • 00:43:38
    i don't want my spoon to uh corrode so i
  • 00:43:41
    cover it i want to cover it with a layer
  • 00:43:43
    of silver
  • 00:43:44
    so i attach it to the end of the battery
  • 00:43:46
    and the other end is attached to a
  • 00:43:48
    silver
  • 00:43:50
    rod and this reaction is called
  • 00:43:52
    electroplating in which the
  • 00:43:54
    reaction will occur and cover the zinc
  • 00:43:56
    with a layer of
  • 00:43:58
    silver of course the let's say when we
  • 00:44:00
    cover the spoon with a layer of silver
  • 00:44:02
    the silver is something that is less
  • 00:44:04
    reactive
  • 00:44:05
    than hydrogen so it does not react with
  • 00:44:08
    oxygen or water vapor in there
  • 00:44:14
    this is a typical question name the
  • 00:44:15
    process used to coat iron with zinc
  • 00:44:17
    remind me again what was this process
  • 00:44:19
    called
  • 00:44:20
    when i cover the iron with zinc by
  • 00:44:23
    dipping or spraying this is called
  • 00:44:25
    galvanizing another question says the
  • 00:44:28
    diagram shows three pieces of iron so he
  • 00:44:30
    has a piece of iron
  • 00:44:32
    not covered with anything a piece of
  • 00:44:34
    iron covered with a layer of zinc
  • 00:44:36
    and sea has the some of the layer of
  • 00:44:39
    zinc
  • 00:44:40
    uh peeled off so the three pieces of
  • 00:44:43
    iron are left in separate troughs of
  • 00:44:44
    water exposed to the atmosphere for
  • 00:44:46
    several weeks
  • 00:44:47
    the table shows the appearance of the
  • 00:44:49
    pieces of iron after several
  • 00:44:51
    weeks so after several weeks a was
  • 00:44:54
    covered in a brown solid so they did
  • 00:44:55
    trust or not
  • 00:44:57
    yes we should know that iron as a metal
  • 00:45:00
    is shiny when it cover it is covered
  • 00:45:02
    with a brown solid that means it has
  • 00:45:04
    crusted now b and c remain shiny
  • 00:45:08
    so that means that b and c do not rust
  • 00:45:11
    the brown solid contains hydrated iron
  • 00:45:14
    iii
  • 00:45:15
    oxide what is the common name for this
  • 00:45:17
    brown solid
  • 00:45:18
    so the hydrated iron iii oxide is what
  • 00:45:21
    we call
  • 00:45:22
    rust identify the two substances that
  • 00:45:25
    react with iron to form the brown solid
  • 00:45:27
    we said iron needs to react with what in
  • 00:45:29
    order to rust
  • 00:45:32
    water and oxygen now explain with
  • 00:45:35
    reference to the symbol in the box the
  • 00:45:37
    symbols in the box
  • 00:45:38
    why the brown solid does not form one
  • 00:45:40
    see now which one was c
  • 00:45:41
    c was the one that was covered with zinc
  • 00:45:44
    but a little piece of the zinc is
  • 00:45:46
    removed so a little piece of the
  • 00:45:48
    iron is exposed but all we still
  • 00:45:52
    said that when a little piece of the
  • 00:45:54
    iron is exposed
  • 00:45:55
    still that will not rust so long as it's
  • 00:46:00
    in contact with some zinc so
  • 00:46:03
    why is that happening we said this is
  • 00:46:06
    because what
  • 00:46:07
    zinc is more reactive than i so it loses
  • 00:46:10
    electrons instead of iron and becomes
  • 00:46:13
    oxidized
  • 00:46:14
    so this does not allow the iron to lose
  • 00:46:17
    electrons remember that i need to use
  • 00:46:18
    the things that are in the box
  • 00:46:20
    and no iron ii plus is formed remember
  • 00:46:23
    we said
  • 00:46:24
    when the ion rusts it changes into ion2
  • 00:46:27
    plus
  • 00:46:28
    so instead of the iron changing to iron
  • 00:46:30
    2 plus it is the zinc that will
  • 00:46:32
    react so the zinc reacts loses electrons
  • 00:46:36
    becomes
  • 00:46:36
    zinc 2 plus instead of the eye
  • 00:46:40
    okay so that's the end of this chapter
  • 00:46:44
    please study it well and try the
  • 00:46:47
    questions that you have in the chapter
  • 00:46:49
    asked questions in the pdf that is very
  • 00:46:51
    important
  • 00:46:52
    it's very important to try the questions
  • 00:46:54
    before you go to the next
  • 00:46:56
    video that discusses the answers to the
  • 00:46:59
    questions
  • 00:47:00
    okay thank you
Tags
  • estructures metàl·liques
  • conductivitat metàl·lica
  • reactivitat química
  • corrosió
  • protecció galvanitzada
  • electrons delocalitzats
  • metalls alcalins
  • rovell
  • reactivitat amb aigua
  • propietats físiques del metall