Name: electroplating with electrolytic cells
Uploaded: 2020-03-26T07:22:26.000Z
Duration: 2 min 52 s
Channel: JoVE

Reakcje elektrochemiczne są niezbędne dla wielu procesów zachodzących w technologii i ludzkim ciele i polegają na przenoszeniu elektronów z jednego rodzaju substancji chemicznej na drugi. Reakcje te nazywane są reakcjami redukcji-utleniania lub reakcjami redoks.
Kiedy gatunek traci elektrony, ulega utlenieniu, a my mówimy, że jest utleniony. Kiedy jakiś gatunek zyskuje elektrony, oznacza to, że uległ redukcji, a my mówimy, że jest zredukowany. W elektrochemicznym ogniwie galwanicznym spontanicznie zachodzą reakcje redoks, w wyniku których powstaje energia elektryczna. Jednak w ogniwie elektrolitycznym stosowana jest energia elektryczna, która powoduje zachodzące reakcje redoks.
Ogniwo elektrolityczne składa się z roztworu reakcyjnego zwanego elektrolitem, który zawiera wszelkie związki chemiczne, które są utleniane lub redukowane, a także jony potrzebne do umożliwienia przepływu elektronów. Ogniwo elektrolityczne posiada dwie metalowe elektrody, które są zanurzone w roztworze elektrolitycznym. Obwód zewnętrzny łączy dwie elektrody, co uzupełnia obwód i umożliwia nam podanie napięcia lub prądu.
Przyłożony prąd lub napięcie jest tym, co powoduje zajście reakcji elektrochemicznej. Półreakcja utleniania zachodzi na anodzie, a półreakcja redukcji zachodzi na katodzie. Aby pomóc Ci je rozróżnić, pamiętaj o wyrażeniu "czerwony kot", które oznacza "redukcję na katodzie".
Ale jak określić, która elektroda jest która? Możemy użyć standardowego potencjału redukcyjnego elektrod metalowych, który jest miarą tendencji metalu do utraty elektronów. Im wyższy potencjał redukcyjny, tym większe prawdopodobieństwo, że metal zostanie zredukowany.
Powiedzmy, że umieszczamy elektrodę srebrną i elektrodę miedzianą w ogniwie elektrolitycznym i przykładamy prąd. Elektroda srebrna ma wyższy potencjał redukcyjny, więc jest zredukowana i działa jak katoda. Elektroda miedziana ma mniejszy potencjał redukcyjny, więc jest utleniona i pełni rolę anody.
Jednym z zastosowań ogniw elektrolitycznych jest galwanizacja, która jest reakcją, w której jeden metal jest utleniany, a następnie redukowany na powierzchnię innego metalu. Ponieważ anoda jest metalem wykonującym powlekanie, w naszym przykładzie srebra i miedzi srebrna elektroda jest pokryta cienką warstwą miedzi.
W tym laboratorium zmontujesz ogniwo elektrolityczne i przeprowadzisz proces galwanizacji, platerując mosiężny klucz miedzią.

ogniwa elektrolityczne

elektrochemia
Elektrochemia to gałąź chemii, która opisuje i mierzy związek między energią elektryczną a zmianą chemiczną. Reakcje elektrochemiczne polegają na przemieszczaniu się elektronów z jednego gatunku do drugiego. Jeśli reakcja jest spontaniczna, może to spowodować wygenerowanie prądu. Jeśli reakcja nie jest spontaniczna, może być napędzana przez zastosowanie prądu.
W elektrochemii kluczową reakcją jest reakcja utleniania-redukcji, zwana reakcją redoks. Reakcja redoks składa się z dwóch półreakcji; utlenianie, w którym substancja znana jako środek redukujący traci elektrony, oraz redukcja, w której substancja znana jako środek utleniający zyskuje elektrony. Reakcje redoks zawsze zachodzą parami i zmieniają stopnie utlenienia atomów w zaangażowanych cząsteczkach. Łatwym sposobem na zapamiętanie tej zależności jest pneumatyczne OIL-RIG: Oxidation Is Losing – Reduction Is Gaining.
<h4>Ogniwa elektrochemiczne</h4>
Ogniwo elektrochemiczne służy do pomiaru lub indukowania reakcji elektrochemicznych. Składa się z kilku elementów: komory zawierającej roztwór reakcyjny, dwóch elektrod przewodzących, przewodzącego roztworu elektrolitu i obwodu zewnętrznego. Istnieją dwa rodzaje ogniw elektrochemicznych. Jednym z nich jest ogniwo elektrolityczne, które wykorzystuje energię elektryczną do napędzania niespontanicznej reakcji. W tego typu ogniwach energia elektryczna jest dostarczana z zewnętrznego źródła zasilania.
Drugim typem ogniw jest ogniwo galwaniczne, które wykorzystuje spontaniczną reakcję elektrochemiczną do wytwarzania energii elektrycznej. Dwie elektrody nazywane są anodą i katodą i są połączone zewnętrznym obwodem. Komora reakcyjna wypełniona jest elektrolitem, który sprzyja przechodzeniu jonów między elektrodami. W ogniwie galwanicznym mostek solny uzupełnia obwód, umożliwiając przepływ jonów między roztworami elektrolitycznymi zawierającymi elektrody. W ogniwie elektrolitycznym nie ma mostka solnego, ponieważ elektrody są zwykle w tym samym roztworze elektrolitycznym.
Reakcja redukcji zachodzi na katodzie, natomiast reakcja utleniania zachodzi na anodzie. Pamięta się to za pomocą mnemonika "Red Cat", co oznacza, że czerwonezapalenie występuje w kocimhode.
<h4>Ogniwa elektrolityczne</h4>
Ogniwa elektrolityczne mają zazwyczaj jedną komorę reakcyjną, w której znajduje się roztwór elektrolitu. Elektrolit jest zwykle roztworem wodnym zawierającym jony lub rozpuszczone sole. Jony w elektrolicie sprzyjają ruchowi jonów i elektronów przez roztwór.
Po przyłożeniu napięcia zewnętrznego jony w elektrolicie są przyciągane do elektrody o przeciwnym ładunku. W tym miejscu zachodzą dwie półreakcje. Anoda traci elektrony podczas utleniania, podczas gdy katoda zyskuje elektrony podczas redukcji.
Galwanizacja to proces, w którym wykorzystuje się ogniwo elektrolityczne. Galwanizacja to proces, w którym jeden metal osadza się na powierzchni elektrody, zwykle inny metal. Brytyjski naukowiec Michael Faraday, od którego pochodzi nazwa stałej Faradaya, zademonstrował molowy związek między jonem naładowanym galwanicznie a prądem elektrycznym. Patrząc na specyficzną półreakcję dla srebra:
Ag+ + 1e- → Ag
Potrzeba jednego mola elektronów, zasilanego przez prąd zewnętrzny, aby zredukować jeden mol kationów srebra do stałego srebra. Dlatego stechiometria reakcji połówkowej może określić ilość materiału galwanicznego użytego do znanej ilości elektronów. Przypomnijmy, że elektryczność nie jest mierzona na podstawie moli elektronów, ale raczej w kulombach, nazwanych na cześć francuskiego inżyniera Charlesa-Augustina de Coulomba. Jeden kulomb to ilość energii elektrycznej przepływającej przez obwód elektryczny o natężeniu 1 ampera prądu w odstępie 1 sekundy, która opiera się na zasadzie ładunku elementarnego lub ładunku, jaki przenosi pojedynczy elektron. Odkrycie Faradaya może zatem powiązać prąd elektryczny z liczbą moli platerowanych przez kation galwaniczny (galwanicznie):
F = eNA
F jest stałą Faradaya, e jest ładunkiem elementarnym wyrażonym w kulombach, aN A jest liczbą Avogadro. Dlatego stała Faradaya jest wyrażona jako liczba kulombów na mol i ma wartość 96485 kulombów na mol. Jak możemy określić liczbę moli elektronów przenoszonych na anodę na podstawie prądu? Korzystając z ładunku elektrycznego Q i definicji kullomba:
<img src="/CDNSource/lm/labs/53/53_Concepts_3.jpg">
Ładunek elektryczny jest równy prądowi w amperach (I) pomnożonemu przez czas w sekundach, w którym prąd mógł płynąć. Dzieląc Q przez stałą Faradaya, która ma jednostki kulombów na mol:
<img src="/CDNSource/lm/labs/53/53_Concepts_4.jpg">
Równanie to pozwala nam obliczyć liczbę moli elektronów, a tym samym określić, jak bardzo kation galwaniczny został zredukowany.
W galwanotechnice metal składa się z płytek anodowych lub pokryw, katody w cienkiej warstwie metalu. Ilość metalu platerowanego zależy od ilości przyłożonego prądu, a także od liczby moli dostępnego kationu galwanicznego. Zewnętrzne źródło zasilania, takie jak bateria, indukuje przepływ elektronów z anody do katody oraz z dodatniego zacisku do ujemnego bieguna akumulatora.
Rozważmy na przykład ogniwo elektrolityczne z elektrodą miedzianą, mosiężnym kluczem działającym jako druga elektroda i wodnym roztworem siarczanu miedzi jako elektrolitem. Tutaj miedź z elektrolitu i elektroda miedziana są platerowane na mosiężnym kluczu.
Aby miedź metaliczna mogła zostać osadzona na mosiężnym kluczu, stała elektroda miedziana musi zostać utleniona w celu wytworzenia jonów miedzi. Następnie kationy miedzi zarówno z elektrody, jak i elektrolitu są redukowane z roztworu, tworząc stałą miedź na mosiężnym kluczu.
Cu2+ + 2e- → Cu(s)
Elektrony do reakcji są odbierane z ujemnego bieguna akumulatora. Tak więc reakcja redukcji zachodzi przy mosiężnym kluczu, podczas gdy reakcja utleniania zachodzi na elektrodzie miedzianej. Stężony i zakwaszony roztwór siarczanu miedzi zwiększa rozpuszczalność; Dlatego im wyższe stężenie roztworu, tym niższa rezystancja i wyższy prąd. Z kolei wyższy prąd pozwala na większe nałożenie jonów miedzi na mosiężny klucz.
Niektóre metale mają większą tendencję do utraty elektronów niż inne. Standardowy potencjał elektrody (E°) substancji jest miarą tendencji substancji do utraty elektronów. Metal o najwyższym potencjale redukcyjnym ma największą tendencję do utraty elektronów; W związku z tym jest najpierw galwanizowany.
<h4>Odwołania</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr, P.M., Townsend, J.R. (2012). Chemia i reaktywność chemiczna. Belmont, Kalifornia: Brooks/Cole, Cengage Learning.</li>
	<li style="font-size:17px">Silberberg, M.S. (2009). Chemia: molekularna natura materii i zmiana. Boston, Massachusetts: McGraw Hill.</li>
</ol>

Ogniwa elektrolityczne

Elektrochemia
Elektrochemia to gałąź chemii, która opisuje i mierzy związek między energią elektryczną a zmianą chemiczną. ...

Education

JoVE Lab Manual

Chemistry

Chemia

Electrolytic Cells

electroplating with electrolytic cells

Electrochemistry links electrical energy with chemical change, and electrolytic cells show how electricity can drive a nonspontaneous reaction. In these reactions, electrons move from one species to another. The key chemistry is a redox reaction, or oxidation-reduction reaction, which happens in two half-reactions.

Oxidation is the loss of electrons, and reduction is the gain of electrons. The substance that loses electrons is the reducing agent, and the substance that gains electrons is the oxidizing agent. Redox reactions always occur in pairs and change the oxidation state of the atoms involved. A simple memory aid is OIL-RIG: oxidation is losing, reduction is gaining.

An electrochemical cell is used to measure or cause electrochemical reactions. It includes a reaction chamber, two conductive electrodes, a conductive electrolyte, and an external circuit. The two main types are electrolytic cells and galvanic cells. An electrolytic cell uses outside electrical energy to drive a nonspontaneous reaction, while a galvanic cell uses a spontaneous reaction to produce electrical energy. The electrodes are the anode and cathode, and the reaction at the cathode is reduction while the reaction at the anode is oxidation. This is often remembered with “Red Cat,” which means reduction occurs at the cathode.

Electrolytic cells usually have one reaction chamber filled with an electrolyte solution. The electrolyte is often an aqueous solution with ions or dissolved salts. These ions help charge move through the solution. When voltage is applied, ions move toward the electrode with the opposite charge, and the two half-reactions occur there. The anode loses electrons during oxidation, and the cathode gains electrons during reduction.

A major use of an electrolytic cell is electroplating. In electroplating, one metal is deposited as a thin layer on the surface of another electrode. Michael Faraday showed the link between the charge of the ions being plated and the electrical current. For silver, the half-reaction is Ag+ + 1e- -&gt; Ag, so one mole of electrons reduces one mole of silver cations to solid silver. This means half-reaction stoichiometry can be used to calculate how much plating occurs for a known amount of charge.

Electricity is measured in coulombs, not in moles of electrons. One coulomb is the amount of electricity that passes through a circuit with 1 ampere of current in 1 second. Faraday’s constant connects these ideas. It is equal to the elementary charge times Avogadro’s number, and it has a value of 96485 coulombs per mole. The electrical charge is found by multiplying current, I, by time in seconds, and dividing Q by Faraday’s constant gives the moles of electrons transferred.

This relationship shows how current controls electroplating. The amount of metal plated depends on the current applied and on how much electroplating cation is available. An external power source, such as a battery, pushes electrons from the anode to the cathode and from the positive terminal to the negative terminal on the battery. In a copper plating example, a copper electrode, a brass key, and aqueous copper sulfate are used. Copper from the electrode and from the solution is deposited onto the brass key.

For copper to coat the key, the solid copper electrode must first be oxidized to copper ions. Then copper cations in the solution are reduced to solid copper on the brass key, following Cu2+ + 2e- -&gt; Cu(s). The electrons come from the negative terminal of the battery. So the brass key is the site of reduction, and the copper electrode is the site of oxidation. A concentrated and acidified copper sulfate solution increases solubility, lowers resistance, and raises the current, which allows more copper to plate onto the key.

Some metals lose electrons more easily than others. The standard electrode potential, E°, measures a substance’s tendency to lose electrons. In electroplating, the metal with the highest reduction potential has the highest tendency to lose electrons, so it is plated first.

Electroplating with Electrolytic Cells

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electrolytic cells

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proper lab notebook keeping

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synthesis of luminol

Luminol Chemiluminescence in Forensics

Luminol chemiluminescence shows how a chemical reaction can produce light and help with blood detection. Chemical reactions may be endothermic or exothermic, depending on whether they absorb or release heat as reactants become products. The enthalpy of a reaction is the energy difference between reactants and products, or ΔH. A positive ΔH means the reaction is endothermic. A negative ΔH means it is exothermic. Many reactions do not happen in a single step. They can pass through intermediates...

esterification

Ester Formation and Everyday Fragrances

Esters are organic compounds with a carbonyl group attached to an oxygen that connects to another alkyl or aryl group. Their general formula is RCOOR'. They are often made by reacting a carboxylic acid with an alcohol in an esterification reaction. In this process, the hydroxyl group of the acid is replaced by an alkyl or aryl group. Many simple esters have familiar fruit and flower smells because their structures are small and less complex. Formic acid and methanol can combine to form methyl...

identification of unknown aldehydes and ketones

identification-of-unknown-aldehydes-and-ketones

Carbonyl Tests for Aldehydes and Ketones

Aldehydes and ketones are carbonyl compounds, which means they contain a C=O functional group. A ketone has two alkyl or aryl groups attached to the carbonyl carbon. Acetone is the simplest ketone, with two methyl groups. An aldehyde is similar, but it has at least one hydrogen attached to the carbonyl carbon. Formaldehyde is the simplest aldehyde, and acetaldehyde has one hydrogen and one methyl group. The carbonyl carbon in both aldehydes and ketones is electrophilic because the oxygen atom...

uv-vis spectroscopy of dyes

How Dyes Absorb Visible Light

Dyes absorb visible light because their molecular structure lets them interact with specific wavelengths. When light hits a substance, some light is absorbed and the rest is reflected or transmitted. The color we see depends on the wavelength that is reflected. A blue substance reflects blue light, around 430 to 480 nm, and absorbs the complementary orange region, around 590 to 630 nm. Compounds that do not absorb in the visible range appear colorless to the human eye. Light also has energy and...

identifying alcohols

Alcohol Tests for Primary, Secondary, and Tertiary

Alcohol tests can help sort alcohols by structure and reactivity. Alcohols are organic molecules with a hydroxyl group attached to an alkyl or aryl group, written as ROH. If the carbon with the hydroxyl group has one R group, the alcohol is primary. If it has two R groups, it is secondary. If it has three R groups, it is tertiary. Alcohols can also be aromatic when they contain a benzene ring. Phenol is the simplest aromatic alcohol. To identify an alcohol, chemists can use its chemical...

chemistry

Comprehensive, curriculum-focused videos for both instructors and students in introductory chemistry lab courses.

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Learn how electrolytic cells drive electroplating, move electrons through redox reactions, and use Faraday’s constant to calculate plated metal.

Electroplating with Electrolytic Cells | JoVE K12

Przygotuj się do nauczania Ogniwa elektrolityczne dzięki temu 3-minutowemu przewodnikowi dla instruktorów. Obejmuje kluczowe kroki przygotowawcze dla laboratorium Chemistry na JoVE Lab Manual.

Przygotowanie instruktora do Ogniwa elektrolityczne w Chemistry - Ponad 2.2K wyświetleń | JoVE Lab Manual

Postępuj zgodnie z procedurami Ogniwa elektrolityczne krok po kroku w tym 9-minutowym filmie z protokołem studenckim. Część kolekcji Chemistry na JoVE Lab Manual.

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Electroplating with Electrolytic Cells

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