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

電気化学反応は、テクノロジーや人体の多くのプロセスに不可欠であり、ある化学種から別の化学種への電子の移動を伴います。これらの反応は、還元酸化反応または酸化還元反応と呼ばれます。
種が電子を失うと、それは酸化を受け、酸化されると私たちは言います。ある種が電子を獲得すると、それは還元され、私たちはそれが減少したと言います。電気化学ガルバニクスセルでは、酸化還元反応が自然に起こり、電気エネルギーが生成されます。しかし、電解槽では電気エネルギーが印加されるため、酸化還元反応が起こります。
電解槽は、電解質と呼ばれる反応液で構成されており、酸化または還元された化学種と、電子の流れを可能にするために必要なイオンが含まれています。電解セルには、電解液に浸された2つの金属電極があります。外部回路が2つの電極を接続し、回路が完成し、電圧または電流を印加できるようになります。
印加された電流または電圧は、電気化学反応を引き起こすものです。酸化半反応は陽極で起こり、還元半反応は陰極で起こります。この 2 つを区別するために、「カソードでの還元」を表す「赤い猫」というフレーズを覚えておいてください。
しかし、どの電極がどれであるかをどのように判断するのでしょうか。金属電極の標準的な還元電位、つまり金属が電子を失う傾向の尺度を使用することができます。還元電位が高いほど、金属が還元される可能性が高くなります。
電解槽に銀電極と銅電極を配置し、電流を流すとしましょう。銀電極は還元電位が高いため、還元されて陰極として機能します。銅電極は還元電位が低いため、酸化されて陽極として機能します。
電解槽の用途の1つは、1つの金属が酸化され、別の金属の表面に還元される反応である電気めっきを行うことです。アノードはメッキを行う金属であるため、銀と銅の例では、銀電極に薄い銅の層がメッキされています。
このラボでは、電解セルを組み立て、真鍮の鍵に銅をめっきして電気めっきプロセスを実行します。

電解セル

電気化学
電気化学は、電気エネルギーと化学変化との関係を記述および測定する化学の一分野です。電気化学反応には、ある種から別の種への電子の移動が含まれます。反応が自発的な場合、電流が発生する可能性があります。反応が自発的でない場合は、電流の印加によって駆動できます。
電気化学では、酸化還元反応と呼ばれる酸化還元反応が重要な反応です。酸化還元反応は、2つの半反応で構成されています。還元剤と呼ばれる物質が電子を失う酸化と、酸化剤と呼ばれる物質が電子を獲得する還元。酸化還元反応は常にペアで起こり、関与する分子内の原子の酸化状態を変化させます。この関係を覚える簡単な方法は、空気圧OIL-RIG:Oxidation Is Losing - Reduction Is Gainingです。
<h4>電気化学セル</h4>
電気化学セルは、電気化学反応を測定または誘導するために使用されます。これは、反応溶液を含むチャンバー、2つの導電性電極、導電性電解質溶液、および外部回路のいくつかのコンポーネントで構成されています。電気化学セルには2つのタイプがあります。1つは電解セルで、電気エネルギーを使用して非自発的な反応を引き起こします。このタイプのセルでは、電気エネルギーは外部電源から供給されます。
他のタイプのセルはガルバニックセルで、自発的な電気化学反応を使用して電気エネルギーを生成します。2つの電極はアノードとカソードと呼ばれ、外部回路によって接続されています。反応チャンバーには電解質が充填されており、電極間のイオンの通過を促進します。ガルバニ電池では、電極を含む電解液間にイオンが流れるようにすることで、塩橋が回路を完成させます。電解セルでは、電極は通常同じ電解液中にあるため、塩橋はありません。
還元反応はカソードで起こり、酸化反応はアノードで起こります。これは、猫の頭で赤い吸引が発生することを意味するニーモニック「レッドキャット」を使用して記憶されます。
<h4>電解セル</h4>
電解槽には通常、電解質溶液を含む反応チャンバーが1つあります。電解質は通常、イオンまたは溶解塩を含む水溶液です。電解質中のイオンは、溶液中のイオンと電子の移動を促進します。
外部電圧が印加されると、電解質中のイオンは反対の電荷で電極に引き寄せられます。ここで2つの半反応が起こります。アノードは酸化中に電子を失い、カソードは還元中に電子を獲得します。
電気めっきは、電解質セルを利用するプロセスです。電気めっきは、1つの金属(通常は別の金属)を電極の表面に堆積させるプロセスです。ファラデー定数の名前の由来となった英国の科学者マイケル・ファラデーは、電気めっきの荷電イオンと電流との間のモル関係を実証しました。銀の具体的な半反応を見ると、次のようになります。
Ag+ + 1e- → Ag
外部電流によって供給される1モルの電子が、1モルの銀カチオンを固体銀に還元するのに必要です。したがって、半反応化学量論は、既知の量の電子に使用される電気めっき材料の量を決定できます。電気は電子のモル数ではなく、フランスのエンジニア、シャルル・オーギュスタン・ド・クーロンにちなんで名付けられたクーロンで測定されることを思い出してください。1クーロンとは、1アンペアの電流が流れる電気回路を1秒間隔で通過する電気の量で、これは基本電荷、つまり1つの電子が運ぶ電荷の原理に基づいています。したがって、ファラデーの発見は、電流を電気めっきカチオンがめっきするモル数に関連付けることができます。
F = eNA
Fはファラデー定数、eはクーロンで表される基本電荷、NAはアボガドロ数です。したがって、ファラデー定数はモルあたりのクーロン数として表され、モルあたり96485クーロンの値を持ちます。電流に基づいて、アノードに転送される電子のモル数をどのように決定できますか?電荷Qとクーロンの定義を使用して、次のようにします。
<img src="/CDNSource/lm/labs/53/53_Concepts_3.jpg">
電荷は、アンペア単位の電流(I)に電流が流れることを許可された秒単位の時間を掛けたものに等しくなります。Qをファラデー定数で割ると、ファラデー定数(1モルあたりのクーロンの単位)が得られます。
<img src="/CDNSource/lm/labs/53/53_Concepts_4.jpg">
この方程式により、電子のモル数を計算し、電気めっきカチオンがどれだけ減少したかを判断できます。
電気めっきでは、金属はアノードプレート、またはカソードを金属の薄層で覆う。金属めっきの量は、印加される電流の量と、利用可能な電気めっきカチオンのモル数に依存します。バッテリーなどの外部電源は、アノードからカソードへ、およびバッテリーのプラス端子からマイナス端子への電子の流れを誘導します。
たとえば、銅電極、2番目の電極として機能する真鍮の鍵、電解質として硫酸銅の水溶液を備えた電解セルを考えてみましょう。ここでは、電解質と銅電極からの銅が真鍮の鍵盤にメッキされています。
真鍮の鍵盤に銅金属を堆積させるには、固体銅電極を酸化して銅イオンを形成する必要があります。次に、電極と電解質の両方からの銅カチオンが溶液から還元され、真鍮の鍵盤上に固体銅が形成されます。
Cu2+ + 2e- → Cu(s)
反応のための電子は、バッテリーの負極端から受け取られます。したがって、還元反応は真鍮の鍵盤で起こり、酸化反応は銅電極で起こります。濃縮および酸性化された硫酸銅溶液は溶解性を高めます。したがって、溶液の濃度が高いほど、抵抗は小さくなり、電流は高くなります。次に、電流が大きいほど、真鍮のキーへの銅イオンのめっきがさらに発生します。
一部の金属は、他の金属よりも電子を失う傾向が強いです。物質の標準電極電位(E°)は、物質が電子を失う傾向の尺度です。還元電位が最も高い金属は、電子を失う傾向が最も高いです。したがって、最初に電気メッキされます。
<h4>参照</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr, P.M., Townsend, J.R. (2012).化学および化学反応性。カリフォルニア州ベルモント:ブルックス/コール、Cengage Learning。</li>
	<li style="font-size:17px">Silberberg, M.S. (2009).化学:物質と変化の分子的性質。マサチューセッツ州ボストン:マグロウヒル。</li>
</ol>

電気化学
電気化学は、電気エネルギーと化学変化との関係を記述および測定する化学の一分野です。...

Education

JoVE Lab Manual

Chemistry

化学

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

lab techniques

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stoichiometry, product yield, and limiting reactants

stoichiometry-product-yield-and-limiting-reactants

Balancing Equations and Reactant Limits

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redox reactions

Oxidation States in Redox Reactions

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ideal gas law

Gas Laws Behind the Ideal Gas Equation

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acid and base concentrations

Acids, Bases, and pH in Titration

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buffers

Buffer pH and the Common Ion Effect

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Reaction Heat, Hess’s Law, and Calorimetry

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Solubility in Water and Other Solvents

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balmer series

Hydrogen Emission Lines

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Absorbance Spectra and Beer-Lambert Analysis

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Reaction Order and Rate Constants

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Reaction Rate, Arrhenius, and Catalysts

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galvanic cells

Battery Power from Redox Reactions

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electrolytic cells

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proper lab notebook keeping

Recording a Reproducible Lab Experiment

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basic organic chemistry techniques

Organic Lab Glassware and Safe Handling

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melting points

How Impurities Change Melting Points

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boiling points

Boiling Point and Vapor Pressure

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recrystallization

Purifying Crystals by Solubility

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extraction

Separating Mixtures with Solvent Extraction

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simple distillation

Separating Liquids by Boiling Point

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steam distillation

Steam Distillation and Low-Boiling Separation

Steam distillation is a separation method for temperature-sensitive organic compounds. It works best when the organic compound is immiscible in water, meaning the two liquids do not mix. The method helps remove the organic molecule from a non-volatile contaminant without using the higher temperatures needed for many other separations. In steam distillation, the immiscible mixture is heated until both water and the volatile organic compound distill together. The vapor rises to a condenser,...

thin-layer chromatography

TLC Separation by Polarity

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column chromatography

Separating Mixtures by Polarity

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hydrolysis of an ester

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synthesis of luminol

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

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Electroplating with Electrolytic Cells

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