Name: oxidation states in redox reactions
Uploaded: 2020-03-26T07:22:24.000Z
Duration: 4 min 56 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry

CHEM.9

CHEM.9.B

Redox Reactions

الأكسدة والاختزال ، وهو اختصار لأكسدة الاختزال ، هو نوع من التفاعل الكيميائي يصنف حسب صافي نقل الإلكترونات. في هذا التفاعل ، يفقد جزيء واحد الإلكترونات ، تسمى الأكسدة ، ويكتسب الجزيء الآخر إلكترونات تسمى الاختزال. 
لمساعدتك على التمييز بين الاثنين ، تذكر عبارة "OIL-RIG" ، والتي تعني "الأكسدة تخسر ، والتخفيض يكتسب". يسمى الجزيء المؤكسد بالعامل المختزل لأنه يقلل من المادة المتفاعلة الأخرى. وبالمثل ، يطلق على الجزيء الذي يتم تقليله اسم العامل المؤكسد لأنه يؤكسد الجزيء الآخر. 
والآن بعد أن تم ترتيب المصطلحات، لنلق نظرة على مثال تفاعل الأكسدة والاختزال، وهو تكوين أكسيد المغنيسيوم المعدني. أثناء التفاعل ، تفقد كل ذرة مغنيسيوم إلكترونين. وبالتالي ، يتأكسد المغنيسيوم. تكتسب كل ذرة أكسجين إلكترونين. وبالتالي ، يتم تقليل الأكسجين. 
ومع ذلك ، ليست كل التفاعلات تفاعلات أكسدة واختزال. على سبيل المثال ، تفاعل أكسيد الكالسيوم مع ثاني أكسيد الكربون لتكوين كربونات الكالسيوم ليس تفاعل أكسدة واختزال. إذن، كيف يمكننا تحديد تفاعل الأكسدة والاختزال؟ 
للقيام بذلك ، نتتبع رقم الأكسدة لكل عنصر أثناء انتقاله من مادة متفاعلة إلى منتج. رقم الأكسدة هو الشحنة الافتراضية التي ستحصل عليها الذرة إذا كانت روابطها بعناصر مختلفة أيونية ، مما يعني أن الإلكترونات مخصصة للذرة الأكثر كهربية. مجموع أعداد الأكسدة في الجزيء يساوي شحنته الكلية. 
دعونا نلقي نظرة على أكسيد المغنيسيوم. إنه مركب محايد ، لذا فإن مجموع أرقام الأكسدة للمغنيسيوم والأكسجين يساوي صفرا. يمكن أن يعطي المغنيسيوم إلكترونين، لذا فإن رقم الأكسدة له هو زائد اثنين. يمكن للأكسجين أن يقبل إلكترونين ، لذا فإن رقم الأكسدة الخاص به يساوي سالب اثنين. 
ماذا عن رد الفعل؟ تحتوي المركبات الأولية المحايدة النقية على عدد أكسدة يساوي صفر. وبالتالي ، يبدأ كل من المغنيسيوم والأكسجين بأرقام أكسدة تساوي صفر. تغيرت أرقام أكسدة المغنيسيوم والأكسجين أثناء التفاعل ، لذا فهذا تفاعل أكسدة واختزال. 
والآن، دعونا نلق نظرة على تفاعل كربونات الكالسيوم الذي رأيناه سابقا. كلا المتفاعلين محايدان ، لذا فإن مجموع أرقام الأكسدة لكلا المركبين يساوي صفرا. كما رأينا مع أكسيد المغنيسيوم، يحتوي الكالسيوم على عدد أكسدة زائد اثنين والأكسجين ناقص اثنين. بعد ذلك، يكون للكربون الموجود في جزيء ثاني أكسيد الكربون عدد أكسدة زائد أربعة، ولكل أكسجين ناقص اثنين. 
ماذا عن المنتج؟ الكالسيوم زائد اثنين والكربون زائد أربعة، تماما كما هو الحال في المواد المتفاعلة. كل أكسجين يساوي سالب اثنين، أي المجموع ناقص ستة، وصافي رقم الأكسدة صفر. نظرا لأن أيا من أرقام الأكسدة لم يتغير ، فهذا ليس تفاعل أكسدة واختزال. 
والآن دعونا نعرض الأنواع الأربعة لتفاعلات الأكسدة والاختزال. الأول هو تفاعل إزاحة واحد ، حيث تزيح ذرة أخرى. سترى هذا في تفاعل الثرمايت، حيث يتم تقليل أحد المعادن، ويتأكسد المعدن الآخر. 
النوع التالي هو تفاعل الاحتراق ، والذي يحدث بين الوقود والمؤكسد لتكوين منتجات مؤكسدة وحرارة. ترى هذا في المختبر أثناء احتراق الميثان بالأكسجين عند استخدام موقد بنسن. 
والثالث هو تفاعل تخليقي، حيث يتحد متفاعلان لتشكيل منتج واحد، كما هو الحال في تخليق الأمونيا، حيث يتم دمج النيتروجين مع الهيدروجين لتكوين الأمونيا. 
أخيرا ، النوع الرابع هو تفاعل التحلل ، حيث يمتص المتفاعل طاقة كافية لكسر روابطه لتكوين مركبات أصغر. هذا ما يحدث مع الألعاب النارية ، حيث تتحلل كلورات البوتاسيوم إلى كلوريد البوتاسيوم والأكسجين بعد التسخين. 
في هذا المختبر ، ستقوم بإجراء وتحديد أنواع مختلفة من تفاعلات الأكسدة والاختزال التي تحول النحاس الصلب إلى أكسيد النحاس ، ثم تعود مرة أخرى إلى النحاس الصلب.

تفاعلات الأكسدة والاختزال

<h4>الأكسدة والاختزال </h4>
يمكن تصنيف بعض التفاعلات الكيميائية على أنها تفاعلات أكسدة اختزال أو تفاعلات أكسدة واختزال. الأكسدة هي عملية المادة ، مثل الذرة أو الجزيء الأيوني ، التي تفقد إلكترونا واحدا أو أكثر ، والاختزال هو عملية اكتساب المادة إلكترونا واحدا أو أكثر. 
<h4>حالات الأكسدة</h4>
كل ذرة في الجزيء لها حالة الأكسدة الخاصة بها أو رقم الأكسدة. تصف حالة الأكسدة مدى أكسدة الجزيء بالنسبة إلى شكله الأولي الحر. يتم التعبير عن حالة الأكسدة على أنها الشحنة التي ستحصل عليها الذرة إذا كانت كل رابطة من روابطها بالعناصر الأخرى أيونية بحتة. هذا يعني أن الإلكترونات الموجودة في الرابطة مخصصة للذرة الأكثر كهربية. يتم تعريف حالة أكسدة الذرة في شكلها الأولي الحر على أنها 0. 
هناك بعض القواعد التي يتم اتباعها لتحديد حالة الأكسدة. عادة ما يكون للعناصر الموجودة في المجموعة الأولى والمجموعة الثانية حالات أكسدة +1 و +2 على التوالي. عادة ما يكون للهيدروجين والأكسجين حالات أكسدة +1 و -2 ، على التوالي ، وعادة ما يكون للهالوجينات حالة أكسدة -1. بالإضافة إلى ذلك ، فإن حالات أكسدة الذرات في الجزيء تضيف دائما ما يصل إلى الشحنة على الجزيء. وبالتالي ، يمكن في كثير من الأحيان استنتاج حالة أكسدة الذرة غير المذكورة أعلاه. على سبيل المثال ، ضع في اعتبارك ثاني أكسيد الكربون (CO 2 ) ، وهو جزيء محايد. إذا ساهم كل من جزيئي الأكسجين في -2 ، فيجب أن تكون حالة أكسدة الكربون +4 لإلغاء -4 من الأكسجين. 
للحصول على نهج أكثر عمومية ، ارسم بنية لويس للجزيء ، وحدد الروابط بين الذرات المختلفة ، وقم بتعيين كل رابطة للذرة الأكثر كهربية. بعد ذلك ، احسب عدد الإلكترونات في كل ذرة ، حيث تساهم كل رابطة بإلكترونين. اطرح عدد الإلكترونات الموجودة حاليا على الذرة من العدد القياسي لإلكترونات التكافؤ لتلك الذرة للحصول على رقم الأكسدة. 
ضع في اعتبارك ثاني أكسيد الكربون مرة أخرى. يحتوي كل أكسجين على زوجين منفردين من الإلكترونات ومتصل بالكربون المركزي بواسطة رابطة مزدوجة. الأكسجين أكثر كهرسلبية من الكربون ، لذلك يتم تعيين كل رابطة C = O ، والتي تمثل أربعة إلكترونات ، للأكسجين. وبالتالي ، يتم تعيين ما مجموعه ثمانية إلكترونات لكل أكسجين (أربعة من الأزواج الوحيدة وأربعة من الرابطة المزدوجة) ، ولا يتم تعيين أي إلكترونات للكربون. العدد الافتراضي لإلكترونات التكافؤ للأكسجين هو ستة ، لذا فإن رقم الأكسدة لكل أكسجين هو 6-8 = -2. العدد الافتراضي لإلكترونات التكافؤ للكربون هو أربعة ، لذا فإن رقم الأكسدة للكربون هو 4 - 0 = +4. 
<h4>تفاعلات الأكسدة والاختزال </h4>
لا تصنف جميع التفاعلات الكيميائية على أنها تفاعل أكسدة واختزال. تفاعل الأكسدة والاختزال هو أي تفاعل يحدث فيه تغير في حالة أكسدة الذرة. وبالتالي ، للتحقق مما إذا كان التفاعل هو تفاعل أكسدة واختزال ، حدد حالات الأكسدة لكل ذرة في المواد المتفاعلة والمنتجات وابحث عن أي تغييرات. 
تتضمن العديد من تفاعلات الأكسدة والاختزال نقل الإلكترونات مباشرة من جزيء أو ذرة إلى أخرى. في هذه التفاعلات ، إذا اكتسب جزيء أو ذرة إلكترونا ، يجب أن يفقد جزيء آخر أو ذرة إلكترونا. إحدى الطرق البسيطة لتذكر تعريفات الأكسدة والاختزال هي من خلال عبارة OIL-RIG ، والتي تعني Oxidation Is L osing – R eduction Is G aining. 
يتم تقليل الجزيء الذي يكتسب إلكترونا ، لكنه يسمى مؤكسد أو عامل مؤكسد لأنه يؤكسد الجزيء الآخر. وبالمثل ، فإن الجزيء الذي يفقد إلكترونا يتأكسد ، لكنه يسمى مختزل أو عامل اختزال لأنه يقلل من الجزيء الآخر. 
هناك أربعة أنواع تفاعل رئيسية تتضمن عادة عمليات الأكسدة والاختزال. 
<ol>
	<li style="font-size:17px">تفاعل الإزاحة الفردي: تزيح الذرة ذرة أخرى تشكل جزءا من مركب ، وتحل محلها. </li>
	<li style="font-size:17px">تفاعل الاحتراق: يتم تقليل المركب بواسطة مؤكسد قوي ، عادة غاز الأكسجين. عادة ما تنتج تفاعلات الاحتراق التي تحدث بين الهيدروكربونات والمركبات العضوية ثاني أكسيد الكربون والماء. </li>
	<li style="font-size:17px">تفاعل التوليف: يشكل نوعان من المواد المتفاعلة منتجا واحدا. </li>
	<li style="font-size:17px">تفاعل التحلل: ينقسم متفاعل واحد إلى ناتجين أو أكثر. </li>
</ol>
<h4>المراجع</h4>
1. هاريس ، دي سي (2015). التحليل الكيميائي الكمي. نيويورك ، نيويورك: دبليو إتش فريمان وشركاه.

الأكسدة والاختزال
يمكن تصنيف بعض التفاعلات الكيميائية على أنها تفاعلات أكسدة اختزال أو تفاعلات أكسدة واختزال. الأكسدة هي عملية ...

Education

JoVE Lab Manual

الكيمياء

oxidation states in redox reactions

Oxidation states help identify redox reactions. In a redox reaction, oxidation is the loss of one or more electrons, and reduction is the gain of one or more electrons. These reactions are often tracked by changes in oxidation state, also called oxidation number.

Each atom in a molecule has an oxidation state. This number shows how oxidized an atom is compared with its free elemental form. It is written as the charge an atom would have if every bond were purely ionic. In that model, bonding electrons are assigned to the more electronegative atom. An atom in its elemental form has an oxidation state of 0.

Several rules help determine oxidation states. Group I elements usually have +1, and Group II elements usually have +2. Hydrogen is typically +1, oxygen is typically -2, and halogens usually are -1. The oxidation states in a molecule or ion must add up to the total charge, so unknown values can often be found from the rest.

Carbon dioxide is a clear example. CO2 is neutral, so its total oxidation states must add to zero. Each oxygen is usually -2, so carbon must be +4 to balance the two oxygens. Another way to find oxidation numbers is to draw the Lewis structure, assign each bond to the more electronegative atom, and count electrons on each atom.

In CO2, oxygen is more electronegative than carbon, so each C=O bond is assigned to oxygen. Each oxygen gets eight electrons total, including lone pairs and bonding electrons. Oxygen has six valence electrons by default, so its oxidation number is 6 - 8 = -2. Carbon has four valence electrons by default and is assigned none, so its oxidation number is 4 - 0 = +4.

A reaction is a redox reaction when an atom’s oxidation state changes from reactants to products. To check for redox, compare oxidation states on both sides of the reaction. Many redox reactions also involve direct electron transfer between atoms or molecules. If one species gains an electron, another must lose one.

The phrase OIL-RIG helps remember the process: oxidation is losing, and reduction is gaining. The species that gains electrons is reduced, but it is also called the oxidizing agent or oxidant because it oxidizes the other species. The species that loses electrons is oxidized, but it is also called the reducing agent or reductant because it reduces the other species.

Four major reaction types often involve redox processes. In single displacement reactions, one atom replaces another atom in a compound. In combustion reactions, a compound is reduced by a strong oxidant, usually oxygen gas, and hydrocarbons or other organic compounds often produce carbon dioxide and water. In synthesis reactions, two reactants form one product. In decomposition reactions, one reactant breaks into two or more products.

Oxidation States in Redox Reactions

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recrystallization

Purifying Crystals by Solubility

Purifying crystals by solubility is a key organic chemistry technique. Recrystallization uses differences in solubility to separate a desired solid product from starting materials, solvent, and impurities. It is one of the three standard purification methods, along with distillation and extraction. Solubility is the maximum amount of a substance that can dissolve in a fixed volume of solvent at a given temperature. Different solutes dissolve in different solvents, and their behavior can vary...

extraction

Separating Mixtures with Solvent Extraction

Solvent extraction is a common way to separate and isolate a target compound in organic chemistry. In this process, a solute moves from one phase to another so it can be separated from unreacted starting materials or impurities. Extraction is also useful when a product is dissolved in a reaction solvent that is hard to remove by evaporation, such as a solvent with a high boiling point. There are three main types of extraction. In solid-liquid extraction, the solute moves from a solid phase...

simple distillation

Separating Liquids by Boiling Point

Separating liquids by boiling point is the goal of distillation. A miscible mixture contains liquids that mix evenly, and it can be heated so that the more volatile liquid evaporates first. Volatility is a liquid’s tendency to vaporize, and boiling begins when bubbles form in the liquid phase. In a closed container, liquid and vapor can reach equilibrium, which means the rate of vaporization equals the rate of condensation. The pressure from the vapor above the liquid is called vapor pressure.

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

Thin-layer chromatography (TLC) separates compounds in a mixture by polarity. It uses the same basic parts as other chromatography methods: a stationary phase, a mobile phase, and the solute. In TLC, the stationary phase is a thin coating on a plate instead of material packed into a column. The stationary phase in most TLC systems is polar silica gel, a form of silicon dioxide. Its surface has OH groups that can form hydrogen bonds. The sample is first spotted on a pencil start line with a...

column chromatography

Separating Mixtures by Polarity

Column chromatography separates compounds in an organic chemistry lab by using differences in physical properties. It is especially useful for microscale separations when less than 10 grams of material is available for analysis. The method can separate a mixture based on solubility, polarity, hydrophobicity, size, and charge. Any chromatography system has three main parts: the stationary phase, the mobile phase, and the sample mixture. In column chromatography, the stationary phase is usually...

hydrolysis of an ester

Soap Formation from Triglycerides

Triglycerides are lipids made of a glycerol backbone linked to three fatty acids. They are common in vegetable oils and animal fats. Plant lipids are the basis of vegetable oils, while animal lipids are used as lard or general sources of fats. A fatty acid has a long carbon chain, usually between 12 and 20 carbons, with a weak organic acid at one end. Some fatty acids contain double bonds. These are unsaturated fats. The double bond usually gives the chain a bent, cis shape. As a result,...

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 oxidation states reveal redox reactions, how to assign oxidation numbers, and why oxidation, reduction, and agents matter in chemistry.

Oxidation States in Redox Reactions | JoVE K12

Florida Department of Education

Physical Science

SC.912.P.8

SC.912.P.8.10

Georgia Standards of Excellence

9-12

SC3.

Indicators of Chemical Reactions

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تحضير المدرّس لـ تفاعلات الأكسدة والاختزال في Chemistry - أكثر من 4.9K مشاهدة | JoVE Lab Manual

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Balancing Redox Equations

Electrochemistry is the science involved in the interconversion of electrical and chemical reactions. Such reactions are called reduction-oxidation, or ...

ionic-compounds-formulas-and-nomenclature

Ionic Compounds: Formulas and Nomenclature

An element composed of atoms that readily lose electrons (a metal) can react with an element composed of atoms that readily gain electrons (a nonmetal) to ...

molecular-compounds-formulas-and-nomenclature

Molecular Compounds: Formulas and Nomenclature

Molecular compounds or covalent compounds result when atoms share electrons to form covalent bonds. Since there is no electron transfer, molecular ...

formula-mass-and-mole-concepts-of-compounds

Formula Mass and Mole Concepts of Compounds

Formula Mass of Covalent Compounds

Chemical formulas represent the elemental makeup of substances. For covalent compounds, the formula represents the ...

experimental-determination-of-chemical-formula

Experimental Determination of Chemical Formula

The elemental makeup of a compound defines its chemical identity, and chemical formulas are the most concise way of representing this elemental makeup. ...

Chemical Equations

Chemical equations represent the identities and relative quantities of substances involved in a chemical reaction. The substances undergoing reaction are ...

CHEM.9.A

Chemical Reactions in Aqueous Solutions

Chemical substances interact in many different ways. Certain chemical reactions exhibit common patterns of reactivity. Due to the vast number of chemical ...

Precipitation Reactions

In a precipitation reaction, aqueous solutions of soluble salts react to give an insoluble ionic compound &#x2013; the precipitate. The reaction occurs ...

Oxidation-Reduction Reactions

Oxidation&ndash;Reduction Reactions

Earth&rsquo;s atmosphere contains about 20% molecular oxygen, O2, a chemically reactive gas that plays an essential ...

Oxidation Numbers

In redox reactions, the transfer of electrons occurs between reacting species. Electron transfer is described by a hypothetical number called the ...

Oxidation and Reduction
Some chemical reactions can be classified as reduction-oxidation reactions, or redox reactions. Oxidation is the process of ...

Acids, Bases and Neutralization Reactions

An acid-base reaction is one in which a hydrogen ion, H+, is transferred from one chemical species to another. Such reactions are of central importance to ...

Reaction Stoichiometry

A balanced chemical equation provides a great deal of information in a very succinct format. Chemical formulas provide the identities of the reactants and ...

Limiting Reactant

The relative amounts of reactants and products represented in a balanced chemical equation are often referred to as stoichiometric amounts. However, in ...

Reaction Yield

The theoretical yield of a reaction is the amount of product estimated to form based on the stoichiometry of the balanced chemical equation. The ...

Stoichiometry, Product Yield, and Limiting Reactants

Chemical equations represent how a chemical reaction proceeds from reactants to products through physical or chemical change using chemical formulas.
...

CHEM.9.C

Science concepts. The student understands how matter is accounted for in chemical reactions. The student is expected to:

Oxidation States in Redox Reactions

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