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

Redoks, który jest skrótem od redukcji-utleniania, to rodzaj reakcji chemicznej klasyfikowanej przez transfer netto elektronów. W tej reakcji jedna cząsteczka traci elektrony, co nazywa się utlenianiem, a druga cząsteczka zyskuje elektrony, co nazywa się redukcją.
Aby ułatwić sobie rozróżnienie tych dwóch, pamiętaj o wyrażeniu "OIL-RIG", które oznacza "utlenianie to tracić, redukcja to zyskiwanie". Cząsteczka, która jest utleniona, nazywana jest środkiem redukującym, ponieważ redukuje drugi reagent. Podobnie cząsteczka, która jest zredukowana, nazywana jest środkiem utleniającym, ponieważ utlenia drugą cząsteczkę.
Teraz, gdy mamy już uporządkowaną terminologię, spójrzmy na przykład reakcji redoks, czyli tworzenia się mineralnego tlenku magnezu. Podczas reakcji każdy atom magnezu traci dwa elektrony. W ten sposób magnez ulega utlenieniu. Każdy atom tlenu zyskuje dwa elektrony; W ten sposób tlen jest redukowany.
Jednak nie wszystkie reakcje są reakcjami redoks. Na przykład reakcja tlenku wapnia z dwutlenkiem węgla w celu wytworzenia węglanu wapnia nie jest reakcją redoks. Jak więc możemy zidentyfikować reakcję redoks?
Aby to zrobić, śledzimy stopień utlenienia każdego pierwiastka w miarę jego przejścia od reagenta do produktu. Liczba utlenienia to hipotetyczny ładunek, jaki miałby atom, gdyby jego wiązania z różnymi pierwiastkami były jonowe, co oznacza, że elektrony są przypisane do bardziej elektroujemnego atomu. Suma stopni utlenienia w cząsteczce jest równa jej całkowitemu ładunkowi.
Wróćmy do tlenku magnezu. Jest to związek obojętny, więc suma stopni utlenienia magnezu i tlenu jest równa zero. Magnez może dać dwa elektrony, więc jego stopień utlenienia wynosi plus dwa. Tlen może przyjąć dwa elektrony, więc jego stopień utlenienia wynosi minus dwa.
A co z reakcją? Czyste neutralne związki elementarne mają stopień utlenienia równy zero. Tak więc zarówno magnez, jak i tlen zaczynają się od zerowych stopni utlenienia. Zarówno stopień utlenienia magnezu, jak i tlenu zmienił się podczas reakcji, więc jest to reakcja redoks.
Spójrzmy teraz na reakcję węglanu wapnia, którą widzieliśmy wcześniej. Oba reagenty są obojętne, więc suma stopni utlenienia dla obu związków wynosi zero. Jak widzieliśmy w przypadku tlenku magnezu, wapń ma stopień utlenienia plus dwa, a tlen minus dwa. Następnie węgiel w cząsteczce dwutlenku węgla ma stopień utlenienia plus cztery, a każdy tlen minus dwa.
A co z produktem? Wapń to plus dwa, a węgiel plus cztery, tak jak w reagentach. Każdy tlen ma wartość minus dwa, co daje w sumie minus sześć, przy liczbie utlenienia netto zerowej. Ponieważ żaden ze stopni utlenienia nie uległ zmianie, nie jest to reakcja redoks.
Przedstawmy teraz cztery rodzaje reakcji redoks. Pierwszą z nich jest reakcja pojedynczego przemieszczenia, w której jeden atom wypiera drugi. Zobaczysz to w reakcji termitu, w której jeden metal jest redukowany, a drugi metal jest utleniany.
Kolejnym typem jest reakcja spalania, która zachodzi między paliwem a utleniaczem w celu wytworzenia produktów utlenionych i ciepła. Widać to w laboratorium podczas spalania metanu z tlenem przy użyciu palnika Bunsena.
Trzecia to reakcja syntezy, w której dwa reagenty łączą się, tworząc jeden produkt, jak w syntezie amoniaku, gdzie azot łączy się z wodorem, tworząc amoniak.
Wreszcie czwarty typ to reakcja rozkładu, w której reagent pochłania wystarczającą ilość energii, aby zerwać swoje wiązania, tworząc mniejsze związki. Tak dzieje się z fajerwerkami, w których chloran potasu po podgrzaniu rozkłada się na chlorek potasu i tlen.
W tym laboratorium wykonasz i zidentyfikujesz różne rodzaje reakcji redoks, które przekształcają stałą miedź w tlenek miedzi, a następnie z powrotem w stałą miedź.

reakcje redoks

<h4>Utlenianie i redukcja</h4>
Niektóre reakcje chemiczne można sklasyfikować jako reakcje redukcji-utleniania lub reakcje redoks. Utlenianie to proces, w którym materia, taka jak atom lub cząsteczka jonowa, traci jeden lub więcej elektronów, a redukcja to proces, w którym materia zyskuje jeden lub więcej elektronów.
<h4>Stany utlenienia</h4>
Każdy atom w cząsteczce ma swój własny stopień utlenienia lub stopień utlenienia. Stopień utlenienia opisuje, jak utleniona jest cząsteczka w stosunku do jej wolnej formy pierwiastkowej. Stopień utlenienia jest wyrażony jako ładunek, jaki miałby atom, gdyby każde z jego wiązań z innymi pierwiastkami było czysto jonowe. Oznacza to, że elektrony w wiązaniu są przypisane do bardziej elektroujemnego atomu. Stopień utlenienia atomu w jego wolnej postaci pierwiastkowej definiuje się jako 0.
Istnieje kilka zasad, których przestrzega się w celu określenia stopnia utlenienia. Pierwiastki z grupy I i grupy II mają zazwyczaj stopnie utlenienia odpowiednio +1 i +2. Wodór i tlen mają zazwyczaj stopnie utlenienia odpowiednio +1 i -2, a halogeny mają zwykle stopień utlenienia -1. Ponadto stopnie utlenienia atomów w cząsteczce zawsze sumują się do ładunku cząsteczki. W ten sposób często można wywnioskować stopień utlenienia atomu, który nie został wymieniony powyżej. Weźmy na przykład dwutlenek węgla (CO2 ), który jest cząsteczką obojętną. Jeśli każda z dwóch cząsteczek tlenu wnosi -2, stopień utlenienia węgla musi wynosić +4, aby zniwelować -4 z tlenu.
Aby uzyskać bardziej ogólne podejście, narysuj strukturę Lewisa cząsteczki, zidentyfikuj wiązania między różnymi atomami i przypisz każde wiązanie do bardziej elektroujemnego atomu. Następnie policz liczbę elektronów na każdym atomie, przy czym każde wiązanie wnosi dwa elektrony. Odejmij liczbę elektronów, które aktualnie znajdują się na atomie, od standardowej liczby elektronów walencyjnych dla tego atomu, aby uzyskać liczbę utlenienia.
Weźmy ponownie pod uwagę dwutlenek węgla. Każdy tlen ma dwie samotne pary elektronów i jest połączony z centralnym węglem podwójnym wiązaniem. Tlen jest bardziej elektroujemny niż węgiel, więc każde wiązanie C=O, które odpowiada za cztery elektrony, jest przypisane do tlenu. W ten sposób każdemu tlenowi przypisano łącznie osiem elektronów (cztery z samotnych par i cztery z wiązania podwójnego), a węglowi nie przypisano żadnego. Domyślna liczba elektronów walencyjnych tlenu wynosi sześć, więc liczba utlenienia dla każdego tlenu wynosi 6 – 8 = -2. Domyślna liczba elektronów walencyjnych dla węgla wynosi cztery, więc liczba utlenienia węgla wynosi 4 – 0 = +4.
<h4>Reakcje redoks</h4>
Nie wszystkie reakcje chemiczne są klasyfikowane jako reakcje redoks. Reakcja redoks to każda reakcja, w której następuje zmiana stopnia utlenienia atomu. Tak więc, aby sprawdzić, czy reakcja jest reakcją redoks, określ stopnie utlenienia każdego atomu w reagentach i produktach i poszukaj wszelkich zmian.
Wiele reakcji redoks polega na przeniesieniu elektronów bezpośrednio z jednej cząsteczki lub atomu do drugiej. W tych reakcjach, jeśli cząsteczka lub atom zyskuje elektron, inna cząsteczka lub atom musi stracić elektron. Jednym z prostych sposobów na zapamiętanie definicji utleniania i redukcji jest wyrażenie OIL-RIG, które oznacza: Oxidation Is Losing – Reduction Is Gaining.
Cząsteczka zyskująca elektron jest redukowana, ale nazywa się ją utleniaczem lub utleniaczem, ponieważ utlenia drugą cząsteczkę. Podobnie cząsteczka, która traci elektron, jest utleniana, ale nazywa się ją reduktorem lub środkiem redukującym, ponieważ redukuje drugą cząsteczkę.
Istnieją cztery główne typy reakcji, które zazwyczaj obejmują procesy redoks.
<ol>
	<li style="font-size:17px">Reakcja pojedynczego przemieszczenia: Atom wypiera inny atom, który jest częścią związku, i zastępuje go.</li>
	<li style="font-size:17px">Reakcja spalania: Związek jest redukowany przez silny utleniacz, zazwyczaj tlen gazowy. Reakcje spalania, które zachodzą między węglowodorami a związkami organicznymi, zazwyczaj wytwarzają dwutlenek węgla i wodę.</li>
	<li style="font-size:17px">Reakcja syntezy: Dwa reagenty tworzą jeden produkt.</li>
	<li style="font-size:17px">Reakcja rozkładu: Pojedynczy reagent rozpada się na dwa lub więcej produktów.</li>
</ol>
<h4>Odwołania</h4>
1. Harris, D. C. (2015). Ilościowa analiza chemiczna. Nowy Jork, NY: W. H. Freeman and Company.

Reakcje redoks

Utlenianie i redukcja
Niektóre reakcje chemiczne można sklasyfikować jako reakcje redukcji-utleniania lub reakcje redoks. Utlenianie to proces ...

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JoVE Lab Manual

Chemia

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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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

Przygotuj się do nauczania Reakcje redoks dzięki temu 6-minutowemu przewodnikowi dla instruktorów. Obejmuje kluczowe kroki przygotowawcze dla laboratorium Chemistry na JoVE Lab Manual.

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Postępuj zgodnie z procedurami Reakcje redoks krok po kroku w tym 15-minutowym filmie z protokołem studenckim. Część kolekcji Chemistry na 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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