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

Elektrokimyasal reaksiyonlar, teknolojideki ve insan vücudundaki birçok süreç için hayati önem taşır ve elektronların bir kimyasal türden diğerine transferini içerir. Bu reaksiyonlara indirgeme-oksidasyon reaksiyonları veya redoks reaksiyonları denir.
Bir tür elektron kaybettiğinde oksidasyona uğrar ve biz onun oksitlendiğini söyleriz. Bir tür elektron kazandığında indirgenme geçirmiştir ve biz onun indirgendiğini söylüyoruz. Elektrokimyasal bir galvanik hücrede, elektrik enerjisi üreten redoks reaksiyonları kendiliğinden meydana gelir. Bununla birlikte, bir elektrolitik hücrede, redoks reaksiyonlarının meydana gelmesine neden olan elektrik enerjisi uygulanır.
Bir elektrolitik hücre, elektron akışını sağlamak için gereken iyonların yanı sıra oksitlenmiş veya indirgenmiş herhangi bir kimyasal türü içeren elektrolit adı verilen reaksiyon çözeltisinden oluşur. Elektrolitik hücre, elektrolitik çözeltiye batırılmış iki metal elektrota sahiptir. Harici bir devre, devreyi tamamlayan ve voltaj veya akım uygulamamızı sağlayan iki elektrotu birbirine bağlar.
Uygulanan akım veya voltaj, elektrokimyasal reaksiyonun gerçekleşmesine neden olan şeydir. Oksidasyon yarı reaksiyonu anotta meydana gelir ve indirgeme yarı reaksiyonu katotta meydana gelir. İkisi arasında ayrım yapmanıza yardımcı olması için, 'katotta azalma' anlamına gelen 'kırmızı kedi' ifadesini hatırlayın.
Peki hangi elektrotun hangisi olduğunu nasıl belirleriz? Metalin elektron kaybetme eğiliminin bir ölçüsü olan metal elektrotların standart indirgeme potansiyelini kullanabiliriz. İndirgeme potansiyeli ne kadar yüksek olursa, metalin indirgenme olasılığı o kadar yüksektir.
Diyelim ki bir elektrolitik hücreye bir gümüş elektrot ve bir bakır elektrot yerleştirdik ve akım uyguladık. Gümüş elektrot daha yüksek bir indirgeme potansiyeline sahiptir, bu nedenle indirgenir ve katot görevi görür. Bakır elektrot daha düşük bir indirgeme potansiyeline sahiptir, bu nedenle oksitlenir ve anot görevi görür.
Elektrolitik hücrelerin bir kullanımı, bir metalin oksitlendiği ve daha sonra başka bir metalin yüzeyine indirgendiği bir reaksiyon olan elektrokaplama yapmaktır. Anot, kaplamayı yapan metal olduğundan, gümüş ve bakır örneğimizde, gümüş elektrot ince bir bakır tabakası ile kaplanır.
Bu laboratuvarda, bir elektrolitik hücreyi bir araya getirecek ve pirinç bir anahtarı bakırla kaplayarak elektrokaplama işlemini gerçekleştireceksiniz.

elektrolitik hücreler

Elektrokimya
Elektrokimya, elektrik enerjisi ile kimyasal bir değişim arasındaki ilişkiyi tanımlayan ve ölçen bir kimya dalıdır. Elektrokimyasal reaksiyonlar, elektronların bir türden diğerine hareketini içerir. Reaksiyon kendiliğinden ise, üretilen bir akıma neden olabilir. Reaksiyon kendiliğinden değilse, akımın uygulanmasıyla sürülebilir.
Elektrokimyada anahtar reaksiyon, redoks reaksiyonu adı verilen oksidasyon-indirgeme reaksiyonudur. Redoks reaksiyonu iki yarı reaksiyondan oluşur; indirgeyici ajan olarak bilinen bir maddenin elektron kaybettiği oksidasyon ve oksitleyici ajan olarak bilinen bir maddenin elektron kazandığı indirgeme. Redoks reaksiyonları her zaman çiftler halinde meydana gelir ve ilgili moleküllerdeki atomların oksidasyon durumlarını değiştirir. Bu ilişkiyi hatırlamanın kolay bir yolu, pnömatik OIL-RIG: Oxidation Is Losing – Reduction Is Gaining'dir.
<h4>Elektrokimyasal Hücreler</h4>
Elektrokimyasal reaksiyonları ölçmek veya indüklemek için bir elektrokimyasal hücre kullanılır. Birkaç bileşenden oluşur: reaksiyon çözeltisini içeren bir oda, iki iletken elektrot, bir iletken elektrolit çözeltisi ve bir harici devre. İki tür elektrokimyasal hücre vardır. Bunlardan biri, spontan olmayan bir reaksiyonu yürütmek için elektrik enerjisi kullanan elektrolitik hücredir. Bu tip hücrelerde elektrik enerjisi harici bir güç kaynağından sağlanır.
Diğer hücre türü, elektrik enerjisi üretmek için kendiliğinden bir elektrokimyasal reaksiyon kullanan galvanik hücredir. İki elektrot anot ve katot olarak adlandırılır ve harici bir devre ile bağlanırlar. Reaksiyon odası, iyonların elektrotlar arasında geçişini destekleyen bir elektrolit ile doldurulur. Galvanik bir hücrede, bir tuz köprüsü, elektrotları içeren elektrolitik çözeltiler arasında iyonların akışına izin vererek devreyi tamamlar. Bir elektrolitik hücrede, elektrotlar tipik olarak aynı elektrolitik çözelti içinde olduğu için tuz köprüsü yoktur.
İndirgeme reaksiyonu katotta meydana gelirken, oksidasyon reaksiyonu anotta meydana gelir. Bu, anımsatıcı "Kırmızı Kedi" kullanılarak hatırlanır, bu da kediyuvasında kırmızıuçun meydana geldiği anlamına gelir.
<h4>Elektrolitik Hücreler</h4>
Elektrolitik hücreler tipik olarak elektrolit çözeltisini içeren bir reaksiyon odasına sahiptir. Elektrolit genellikle iyonlar veya çözünmüş tuzlar içeren sulu bir çözeltidir. Elektrolitteki iyonlar, iyonların ve elektronların çözelti boyunca hareketini teşvik eder.
Harici bir voltaj uygulandığında, elektrolitteki iyonlar zıt yükle elektroda çekilir. İki yarı reaksiyonun meydana geldiği yer burasıdır. Anot oksidasyon sırasında elektron kaybederken, katot indirgeme sırasında elektron kazanır.
Elektrokaplama, bir elektrolitik hücre kullanan bir işlemdir. Elektrokaplama, bir metalin bir elektrotun, tipik olarak başka bir metalin yüzeyinde biriktirildiği bir işlemdir. Faraday sabitinin adını aldığı İngiliz bilim adamı Michael Faraday, galvanik yüklü iyon ile elektrik akımı arasındaki molar ilişkiyi gösterdi. Gümüş için spesifik yarı reaksiyona bakıldığında:
Ag+ + 1e- → Ag
Bir mol gümüş katyonunu katı gümüşe indirgemek için harici bir akım tarafından sağlanan bir mol elektron gerekir. Bu nedenle, yarı reaksiyon stokiyometrisi, bilinen bir miktar elektron için kullanılan elektrokaplama malzemesinin miktarını belirleyebilir. Elektriğin elektronların mollerine göre değil, Fransız mühendis Charles-Augustin de Coulomb'un adını taşıyan coulomb cinsinden ölçüldüğünü hatırlayın. Bir coulomb, temel yük veya tek bir elektronun taşıdığı yük ilkesine dayanan, 1 saniyelik bir aralıkta 1 amper akımla bir elektrik devresinden geçen elektrik miktarıdır. Faraday'ın keşfi bu nedenle elektrik akımını elektrokaplama katyonunun kapladığı mol sayısıyla ilişkilendirebilir:
F = eNA
F, Faraday sabitidir, e, coulomb cinsinden ifade edilen temel yüktür ve NA, Avogadro sayısıdır. Bu nedenle, Faraday sabiti mol başına coulomb sayısı olarak ifade edilir ve mol başına 96485 coulomb değerine sahiptir. Akıma bağlı olarak anoda aktarılan elektronların mol sayısını nasıl belirleyebiliriz? Elektrik yükü Q'yu ve bir coulomb'un tanımını kullanarak:
<img src="/CDNSource/lm/labs/53/53_Concepts_3.jpg">
Elektrik yükü, amper (I) cinsinden akımın, akımın akmasına izin verilen saniye cinsinden süre ile çarpımına eşittir. Q'yu mol başına coulomb birimlerine sahip olan Faraday sabitine bölerek:
<img src="/CDNSource/lm/labs/53/53_Concepts_4.jpg">
Bu denklem, elektronların mol sayısını hesaplamamıza ve böylece elektrokaplama katyonunun ne kadarının azaldığını belirlememize izin verir.
Elektrokaplamada metal, anot plakalarını veya örtüleri, katodu ince bir metal tabakası içinde içerir. Metal kaplama miktarı, uygulanan akım miktarına ve mevcut elektrokaplama katyonunun mol sayısına bağlıdır. Pil gibi harici bir güç kaynağı, elektronların anottan katoda ve pozitif terminalden pil üzerindeki negatif terminale akışını indükler.
Örneğin, bakır elektrotlu bir elektrolitik hücre, ikinci elektrot görevi gören bir pirinç anahtar ve elektrolit olarak sulu bir bakır sülfat çözeltisi düşünün. Burada, elektrolitten ve bakır elektrottan gelen bakır, pirinç anahtarın üzerine kaplanır.
Bakır metalin pirinç anahtar üzerine bırakılması için, katı bakır elektrotun bakır iyonları oluşturacak şekilde oksitlenmesi gerekir. Daha sonra, hem elektrottan hem de elektrolitten gelen bakır katyonları, pirinç anahtar üzerinde katı bakır oluşturmak için çözeltiden indirgenir.
Cu2+ + 2e- → Cu(lar)
Reaksiyon için elektronlar, pilin negatif terminalinden alınır. Böylece, indirgeme reaksiyonu pirinç anahtarda meydana gelirken, oksidasyon reaksiyonu bakır elektrotta meydana gelir. Konsantre ve asitleştirilmiş bakır sülfat çözeltisi çözünürlüğü arttırır; Bu nedenle, çözeltinin konsantrasyonu ne kadar yüksek olursa, direnç o kadar düşük ve akım o kadar yüksek olur. Buna karşılık, daha yüksek bir akım, bakır iyonlarının pirinç anahtar üzerine daha fazla kaplanmasına izin verir.
Bazı metallerin elektron kaybetme eğilimi diğerlerinden daha fazladır. Bir maddenin standart elektrot potansiyeli (E°), bir maddenin elektron kaybetme eğiliminin ölçüsüdür. En yüksek indirgeme potansiyeline sahip metal, elektron kaybetme eğilimi en yüksek olandır; Bu nedenle, önce elektrolizle kaplanır.
<h4>Başvuru</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr, P.M., Townsend, J.R. (2012). Kimya ve Kimyasal Reaktivite. Belmont, CA: Brooks/Cole, Cengage Öğrenme.</li>
	<li style="font-size:17px">Silberberg, M.S. (2009). Kimya: Maddenin ve Değişimin Moleküler Doğası. Boston, MA: McGraw Tepesi.</li>
</ol>

Elektrolitik Hücreler

Elektrokimya
Elektrokimya, elektrik enerjisi ile kimyasal bir değişim arasındaki ilişkiyi tanımlayan ve ölçen bir kimya dalıdır. ...

Education

JoVE Lab Manual

Chemistry

Kimya

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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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

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Electroplating with Electrolytic Cells

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