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

Elektrochemische Reaktionen sind für viele Prozesse in der Technik und im menschlichen Körper von entscheidender Bedeutung und beinhalten die Übertragung von Elektronen von einer chemischen Spezies auf eine andere. Diese Reaktionen werden als Reduktions-Oxidationsreaktionen oder Redoxreaktionen bezeichnet.
Wenn eine Spezies Elektronen verliert, oxidiert sie, und wir sagen, dass sie oxidiert ist. Wenn eine Spezies Elektronen gewinnt, hat sie eine Reduktion erfahren, und wir sagen, dass sie reduziert wird. In einer elektrochemischen galvanischen Zelle kommt es spontan zu Redoxreaktionen, die elektrische Energie erzeugen. In einer Elektrolysezelle wird jedoch elektrische Energie zugeführt, die die Redoxreaktionen hervorruft.
Eine Elektrolysezelle besteht aus der Reaktionslösung, dem sogenannten Elektrolyten, der alle chemischen Spezies enthält, die oxidiert oder reduziert werden, sowie Ionen, die zum Ermöglichen des Elektronenflusses benötigt werden. Die Elektrolysezelle besteht aus zwei Metallelektroden, die in die elektrolytische Lösung eingetaucht sind. Eine externe Schaltung verbindet die beiden Elektroden, die den Stromkreis vervollständigt und es uns ermöglicht, Spannung oder Strom anzulegen.
Der angelegte Strom oder die angelegte Spannung ist das, was die elektrochemische Reaktion bewirkt. Die Oxidationshalbreaktion findet an der Anode statt, die Reduktionshalbreaktion an der Kathode. Um Ihnen bei der Unterscheidung zu helfen, denken Sie an den Ausdruck "rote Katze", der für "Reduktion an der Kathode" steht.
Aber wie bestimmen wir, welche Elektrode welche ist? Wir können das Standardreduktionspotential der Metallelektroden verwenden, das ein Maß für die Tendenz des Metalls ist, Elektronen zu verlieren. Je höher das Reduktionspotenzial, desto wahrscheinlicher ist es, dass das Metall reduziert wird.
Nehmen wir an, wir platzieren eine Silberelektrode und eine Kupferelektrode in einer Elektrolysezelle und legen Strom an. Die Silberelektrode hat ein höheres Reduktionspotential, ist also reduziert und fungiert als Kathode. Die Kupferelektrode hat ein geringeres Reduktionspotential, wird also oxidiert und fungiert als Anode.
Eine Verwendung von Elektrolysezellen ist die Galvanik, eine Reaktion, bei der ein Metall oxidiert und dann auf die Oberfläche eines anderen Metalls reduziert wird. Da die Anode das Metall ist, das die Beschichtung übernimmt, ist die Silberelektrode in unserem Beispiel von Silber und Kupfer mit einer dünnen Schicht Kupfer überzogen.
In diesem Labor baust du eine Elektrolysezelle zusammen und führst den Galvanisierungsprozess durch, indem du einen Messingschlüssel mit Kupfer plattierst.

elektrolytzellen

Elektrochemie
Die Elektrochemie ist ein Teilgebiet der Chemie, das die Beziehung zwischen elektrischer Energie und einer chemischen Veränderung beschreibt und misst. Elektrochemische Reaktionen beinhalten die Bewegung von Elektronen von einer Spezies zur anderen. Handelt es sich um eine spontane Reaktion, kann es zu einem erzeugten Strom kommen. Wenn die Reaktion nicht spontan ist, kann sie durch die Anwendung von Strom angetrieben werden.
In der Elektrochemie ist die Schlüsselreaktion die Oxidations-Reduktions-Reaktion, die als Redoxreaktion bezeichnet wird. Die Redoxreaktion setzt sich aus zwei Halbreaktionen zusammen; Oxidation, bei der eine Substanz, die als Reduktionsmittel bekannt ist, Elektronen verliert, und Reduktion, bei der eine Substanz, die als Oxidationsmittel bekannt ist, Elektronen gewinnt. Redoxreaktionen laufen immer paarweise ab und verändern die Oxidationsstufen der Atome in den beteiligten Molekülen. Eine einfache Möglichkeit, sich an diesen Zusammenhang zu erinnern, ist die pneumatische OIL-RIG: Oxidation Is Losing – Reduction Is Gaining.
<h4>Elektrochemische Zellen</h4>
Eine elektrochemische Zelle wird verwendet, um elektrochemische Reaktionen zu messen oder zu induzieren. Es besteht aus mehreren Komponenten: einer Kammer, die die Reaktionslösung enthält, zwei leitfähigen Elektroden, einer leitfähigen Elektrolytlösung und einem externen Kreislauf. Es gibt zwei Arten von elektrochemischen Zellen. Eine davon ist die Elektrolysezelle, die elektrische Energie nutzt, um eine nichtspontane Reaktion auszulösen. Bei diesem Zelltyp wird elektrische Energie von einer externen Stromquelle zugeführt.
Der andere Zelltyp ist die galvanische Zelle, die durch eine spontane elektrochemische Reaktion elektrische Energie erzeugt. Die beiden Elektroden werden Anode und Kathode genannt und sind durch einen externen Stromkreis verbunden. Die Reaktionskammer ist mit einem Elektrolyten gefüllt, der den Durchgang von Ionen zwischen den Elektroden fördert. In einer galvanischen Zelle vervollständigt eine Salzbrücke den Kreislauf, indem sie den Ionenfluss zwischen den elektrolytischen Lösungen, die die Elektroden enthalten, ermöglicht. In einer Elektrolysezelle gibt es keine Salzbrücke, da sich die Elektroden typischerweise in der gleichen elektrolytischen Lösung befinden.
Die Reduktionsreaktion findet an der Kathode statt, während die Oxidationsreaktion an der Anode stattfindet. Dies wird durch die Eselsbrücke "Rote Katze" erinnert, was bedeutet, dass die roteGlut an der Katzenladestattfindet.
<h4>Elektrolytzellen</h4>
Elektrolysezellen haben typischerweise eine Reaktionskammer, die die Elektrolytlösung enthält. Der Elektrolyt ist in der Regel eine wässrige Lösung, die Ionen oder gelöste Salze enthält. Die Ionen im Elektrolyten fördern die Bewegung von Ionen und Elektronen durch die Lösung.
Wenn eine externe Spannung angelegt wird, werden Ionen im Elektrolyten mit der entgegengesetzten Ladung von der Elektrode angezogen. Hier finden die beiden Halbreaktionen statt. Die Anode verliert bei der Oxidation Elektronen, während die Kathode bei der Reduktion Elektronen hinzugewinnt.
Die Galvanik ist ein Prozess, bei dem eine Elektrolysezelle verwendet wird. Die Galvanik ist ein Prozess, bei dem ein Metall auf der Oberfläche einer Elektrode abgeschieden wird, typischerweise ein anderes Metall. Der britische Wissenschaftler Michael Faraday, nach dem die Faraday-Konstante benannt ist, wies die molare Beziehung zwischen dem galvanisch geladenen Ion und dem elektrischen Strom nach. Schauen wir uns die spezifische Halbreaktion für Silber an:
Ag+ + 1e- → Ag
Es braucht ein Mol Elektronen, das von einem externen Strom zugeführt wird, um ein Mol Silberkationen in festes Silber zu reduzieren. Daher kann mit der Halbreaktions-Stöchiometrie die Menge des Galvanikmaterials bestimmt werden, die für eine bekannte Menge an Elektronen verwendet wird. Zur Erinnerung: Elektrizität wird nicht anhand der Mole von Elektronen gemessen, sondern in Coulomebs, benannt nach dem französischen Ingenieur Charles-Augustin de Coulomb. Ein Coulomb ist die Menge an Elektrizität, die mit 1 Ampere Strom über einen Zeitraum von 1 Sekunde durch einen Stromkreis fließt, die auf dem Prinzip der Elementarladung basiert, oder die Ladung, die ein einzelnes Elektron trägt. Faradays Entdeckung kann daher den elektrischen Strom mit der Anzahl der Mol in Beziehung setzen, die das galvanische Kation plattierte:
F = eNA
F ist die Faraday-Konstante, e ist die Elementarladung, die in Coulombs ausgedrückt wird, und NA ist die Avogadro-Zahl. Daher wird die Faradaysche Konstante als Anzahl der Coulomb pro Mol ausgedrückt und hat einen Wert von 96485 Coulomb pro Mol. Wie kann man die Anzahl der Mol Elektronen bestimmen, die auf die Anode übertragen werden, basierend auf dem Strom? Unter Verwendung der elektrischen Ladung Q und der Definition eines Coulombs:
<img src="/CDNSource/lm/labs/53/53_Concepts_3.jpg">
Die elektrische Ladung ist gleich dem Strom in Ampere (I) multipliziert mit der Zeit in Sekunden, die der Strom fließen durfte. Indem man Q durch die Faraday-Konstante dividiert, die die Einheiten von Coulomb pro Mol hat:
<img src="/CDNSource/lm/labs/53/53_Concepts_4.jpg">
Diese Gleichung ermöglicht es uns, die Anzahl der Mol Elektronen zu berechnen und somit zu bestimmen, wie stark das galvanische Kation reduziert wurde.
Bei der Galvanik besteht das Metall aus den Anodenplatten oder bedeckt die Kathode mit einer dünnen Metallschicht. Die Menge des plattierten Metalls hängt von der Menge des angelegten Stroms sowie der Anzahl der Mol des verfügbaren Galvanikkations ab. Eine externe Energiequelle, wie z. B. eine Batterie, induziert den Elektronenfluss von der Anode zur Kathode und vom Pluspol zum Minuspol der Batterie.
Stellen Sie sich zum Beispiel eine Elektrolysezelle mit einer Kupferelektrode, einem Messingschlüssel als zweite Elektrode und einer wässrigen Lösung aus Kupfersulfat als Elektrolyt vor. Hierbei wird Kupfer aus dem Elektrolyten und der Kupferelektrode auf den Messingschlüssel plattiert.
Damit sich das Kupfermetall auf dem Messingschlüssel abscheiden kann, muss die massive Kupferelektrode oxidiert werden, um Kupferionen zu bilden. Dann werden die Kupferkationen sowohl von der Elektrode als auch vom Elektrolyten aus der Lösung reduziert, um auf dem Messingschlüssel festes Kupfer zu bilden.
Cu2+ + 2e- → Cu(s)
Die Elektronen für die Reaktion werden vom Minuspol der Batterie empfangen. So findet die Reduktionsreaktion an der Messingklappe statt, während die Oxidationsreaktion an der Kupferelektrode stattfindet. Die konzentrierte und angesäuerte Kupfersulfatlösung erhöht die Löslichkeit; Je höher die Konzentration der Lösung, desto geringer ist der Widerstand und desto höher der Strom. Ein höherer Strom wiederum ermöglicht eine stärkere Beschichtung der Kupferionen auf dem Messingschlüssel.
Einige Metalle neigen stärker als andere, Elektronen zu verlieren. Das Standardelektrodenpotential (E°) einer Substanz ist das Maß für die Tendenz einer Substanz, Elektronen zu verlieren. Das Metall mit dem höchsten Reduktionspotential hat die höchste Tendenz, Elektronen zu verlieren; Somit wird es zuerst galvanisiert.
<h4>Referenzen</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr., P.M., Townsend, J.R. (2012). Chemie und chemische Reaktivität. Belmont, Kalifornien: Brooks/Cole, Cengage Lernen.</li>
	<li style="font-size:17px">Silberberg, M.S. (2009). Chemie: Die molekulare Natur von Materie und Veränderung. Boston, MA: McGraw Hill.</li>
</ol>

Elektrolytzellen

Elektrochemie
Die Elektrochemie ist ein Teilgebiet der Chemie, das die Beziehung zwischen elektrischer Energie und einer chemischen Veränderung beschreibt und misst. ...

Education

Lehre

JoVE Lab Manual

Chemistry

Chemie

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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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

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Electroplating with Electrolytic Cells

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