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Questions tagged [redox]

Redox is the portmanteau of reduction and oxidation. This tag should be used in questions where both the reduction and the oxidation process are under focus. This tag is not limited to inorganic chemistry. If the question is specifically about either reduction or oxidation (not both) of an organic compound, use [organic-reduction] or [organic-oxidation] instead.

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Why is it important to use a salt bridge in a voltaic cell? Can a wire be used?

I was learning about voltaic cells and came across salt bridges. If the purpose of the salt bridge is only to move electrons from an electrolyte solution to the other, then why can I not use a wire? ...
6
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1answer
2k views

Cr(II) and Mn(III) - their oxidizing and reducing properties?

My textbook states that $\ce{Cr^2+}$ is a reducing agent while $\ce{Mn^3+}$ is an oxidizing agent in spite of both having $\ce{d^4}$ configuration. The explanation states that when $\ce{Cr^2+}$ gets ...
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2answers
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Reaction mechanism of combustion of hydrogen

After a discussion about the usefulness of hydrogen fuel for cars with a friend of mine, I wondered what the reaction mechanism for combustion of $\ce{H2}$ was. I only study (well almost) organic ...
9
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2answers
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How does copper reduce dilute nitric acid to nitric oxide and concentrated nitric acid to nitrogen dioxide?

Here are the 2 equations: \begin{align} \ce{3Cu + 2NO3- + 8H+ &<=> 3Cu^2+ + 2NO + 4H2O} & E &= 0.62~\mathrm{V}\\ \ce{3Cu + 2NO3- + 4H+ &<=> 3Cu^2+ + 2NO2 + 2H2O}& E &...
3
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1answer
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Why do sodium halides react so differently with sulfuric acid?

Why do sodium halides react so differently with sulfuric acid? \begin{align} \ce{NaF + H2SO4 &-> NaHSO4 + HF} \tag{1a}\label{NaF}\\ \ce{NaCl + H2SO4 &-> NaHSO4 + HCl} \tag{...
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2answers
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Why don't everyday things burn?

Ok, so I learned about the equilibrium constant. Now, I've seen that the equilibrium constant of burning is extremely small $(K \ll 1)$. here, I have a question. you see, $K$ is still NOT 0, which ...
17
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1answer
11k views

Migratory aptitude in Baeyer-Villiger reaction

In short, I do not understand how or why the migratory aptitude is as listed in every textbook I've read. Firstly, they talk about a positive charge being built up that is stabilised by the movement ...
10
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1answer
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How to balance more complex redox reactions?

I'm in an advanced level chemistry course, and so far we've been introduced to balancing redox reactions. The basic ones like $$\ce{MnO4- + Cl- -> Mn^2+ + Cl2}\tag1$$ are pretty easy for me, but ...
12
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2answers
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HI/P reduction mechanism

I recently answered a question about Breaking Bad's initial methamphetamine production method (i.e. the reduction of (pseudo)ephedrine). The reaction is as follows: (Source) It is infamously known ...
6
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1answer
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Why is the water reduction of oxygen favored in acidic conditions?

The standard reduction potential of diatomic oxygen in acidic conditions is +1.23 volts. However, the standard reduction potential of diatomic oxygen in basic conditions is only +0.40 volts. Why is ...
8
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4answers
307 views

What is the simplest approach to balance a complex reaction equation?

Consider the redox reaction: $$\begin{multline} \ce{ a K4Fe(CN)6 + b Ce(NO3)4 + c KOH ->\\ d Ce(OH)3 + e Fe(OH)3 + f H2O + g K2CO3 + h KNO3} \end{multline}$$ The book's answer for the ...
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1answer
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Difference in the functioning of alkaline and acidified KMnO4

What is the difference in the functioning of alkaline and acidified $\ce{KMnO4}$ as a reagent in organic chemistry? E.g., in the oxidation of a primary alcohol to carboxylic acid, we use acidified $\...
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3answers
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Why do Electrons leave the Zinc in a Galvanic Cell

What induces electrons to leave the atoms around the part of the zinc metal in a solution to travel up along that zinc metal and above the solution, through the wire and to the copper metal and ...
9
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3answers
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Why is chloride oxidised instead of water in copper chloride electrolysis?

For the Electrolysis of Copper Chloride: Cathode: $\ce{Cu^{2+} + 2e- <=> Cu}$ Anode: $\ce{2Cl <=> Cl2 + 2e- }$ I am confused about the reaction taking place at the anode. Wouldn't $\ce{...
12
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2answers
394 views

Why do oxidation numbers work?

I understand that oxidation numbers are a method for keeping track of electrons in a reaction and how they are generally assigned (electrons in a bond are assigned to the more electronegative atom). ...
9
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4answers
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Which electrodes do not corrode at all?

I had used spare pieces of metal to perform electrolysis. They all had the disadvantage that they corrode when used as anode - and some of the oxides are toxic (copper, chromium). I've found that ...
6
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1answer
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What is the reaction between oxalic acid and potassium permanganate?

I've already searched online some information about this equation, but everywhere I read, there's also sulfuric acid, which we did not use in the laboratory. We only used potassium permanganate and ...
6
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1answer
3k views

Formation of ferrous chloride or ferric chloride

Question When $\ce{HCl}$ reacts with finely powdered iron, it forms ferrous chloride and not ferric chloride. Why? Answer. Its reaction with iron produces $\ce{H2}$. $\ce{Fe + 2HCl -> ...
4
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2answers
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Why is maltose a reducing sugar but not sucrose, even though they're both disaccharides?

I came across this on Wikipedia: Many disaccharides, like cellobiose, lactose and maltose, also have a reducing form, as one of the two units may have an open-chain form with an aldehyde group. ...
11
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3answers
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Reduction of α,β-unsaturated nitro compounds

Would it be possible to reduce a α,β-unsaturated nitro compound to a saturated amine using for example $\ce{NaBH4}$? I know these kind of compounds will be reduced by hydrogenation using a $\ce{Pt/C}$ ...
6
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2answers
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Why does temperature affect cell potential?

The Nernst equation describes the relationship between cell potential and temperature. But why does temperature affect cell potential? My understanding is that the collision model of kinetics is not ...
4
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2answers
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When a molecule loses hydrogen atoms, does it become oxidised?

I had the following question on a bio test covering cell respiration and glycolysis, but I'm not sure if I agree with the answer. When a molecule loses hydrogen atoms (as opposed to hydrogen ions),...
4
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1answer
7k views

Mechanism for oxidation of primary alcohols to carboxylic acids

My teacher told me that the following is the mechanism for oxidation of primary alcohols to carboxylic acids: I've searched in books and online and didn't find a similar mechanism. For example, in ...
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1answer
153 views

Multiple solutions in the balancing of redox reactions

While looking at the reaction between potassium permanganate and hydrogen peroxide in the presence of sulfuric acid a friend and I were attempting to find a general equation to yield the coefficients ...
19
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4answers
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Why is salt needed when using vinegar to clean pennies?

Let's say you have a solution that is vinegar and it has salt (NaCl) dissolved in it. Then you place old dull pennies in it. Then you look at it 5 minutes later and the pennies are clean and looking ...
13
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3answers
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Why iron reacts differently with concentrated and dilute sulfuric acid?

When $\ce{H2SO4}$ is dilute, $ \ce{Fe +H2SO4 -> FeSO4 + H2} $ and when $\ce{H2SO4}$ is concentrated, $\ce{3Fe +8H2SO4 -> FeSO4 + Fe2(SO4)3 + 4SO2 +8H2O}$ What made the reaction with ...
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2answers
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Why do the alkali metals form different products upon combustion in air?

From Wikipedia's article on sodium: When burned in dry air, it forms primarily sodium peroxide with some sodium oxide. We know that sodium has a strong reducing capacity, so why does it produce a ...
20
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3answers
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Please explain why dioxygen difluoride is so dangerous

I just read this article that mentioned that dioxygen difluoride is very dangerous. The terms it uses are "awful", "violently hideous" and "deeply alarming". But I couldn't get a handle on exactly ...
8
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1answer
4k views

Why do alpha-hydroxy ketones respond positively to Tollen's, Fehling's, Benedict's, Schiff's and HgCl2 tests?

I learnt from a certain textbook that aldehydes and formic acid respond positively to Tollen's, Fehling's, Benedict's, Schiff's and HgCl2 tests. However, in another textbook I read that even alpha-...
9
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3answers
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Mechanism for reaction of Tollens' reagent with aldehydes

Upon treatment with Tollens' reagent (ammoniacal silver(I) nitrate), aldehydes are oxidised to carboxylic acid, and silver(I) is reduced to silver metal. I am trying to find a mechanism for the this ...
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1answer
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How does a Lewis acid differ from an oxidizing agent; Lewis bases from reducing agents?

A Lewis acid is defined as an electron acceptor. An oxidizing agent is also defined as an electron acceptor (in the electronic theory of oxidation). So then what is the basic difference between an ...
11
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1answer
667 views

Why is KI oxidized by H2SO4, whereas NaBr isn't oxidised?

My textbook says that alcohols react with sodium bromide and sulphuric acid to form the corresponding alkyl bromides. At the same time they also mention that sulphuric acid mustn't be used with ...
8
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1answer
943 views

Weird Wikipedia Section on Oxidizing Behavior of Nitric and Sulfuric Acids

It has been my understanding that when nitric, perchloric, or sulfuric acids act as oxidizing agents, they must exist as whole $\ce{HNO_3}$ or $\ce{HClO_4}$ or $\ce{H_2SO_4}$ molecules that are still ...
6
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2answers
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Why doesn't hydrogen displace metals from their oxides?

As I understand it, a displacement reaction is where a more reactive element kicks out a less reactive element from a compound. For example, chlorine is more reactive than iodine, so chlorine will ...
11
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1answer
12k views

Why does HNO3 not give off H2 when reacting with Cu?

A dilute solution of which acid is most likely to produce a reduction product other than $\ce{H_{2}}$ when it reacts with a metal? (A) $\ce{HF}$ (B) $\ce{HCl}$ (C) $\ce{HNO3} $ ...
9
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1answer
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Mechanism of the oxidation of alcohols with KMnO4

Many oxidising agents, like chromate, dichromate, iodine in $\ce{NaOH}$ etc. seem to work via ester formation and elimination. For example, chromic acid will react with the $\ce{-OH}$ of alcohol to ...
14
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2answers
16k views

What is formed when you leave iron(II) sulfate in plain air?

What is formed when you leave iron(II) sulfate in plain air? Knowing that iron(II) is easily oxidised to iron(III), and assuming that the reactive component of air is oxygen, I solved it this way: $...
8
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1answer
6k views

Disproportionation of hydrogen peroxide

Hydrogen peroxide is decomposed as follows: $$\ce{2H2O2 -> 2H2O +O2}$$ This is a disproportionation redox reaction of $\ce{H2O2}$ involving the 2 half reactions $$\ce{H2O2 -> O2 + 2H^+ + 2e-}$$ $...
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2answers
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Does Br2/H2O oxidize all aldehydes?

In many books, it is mentioned that aldehydes are easily oxidized even by mild oxidizing agents. However, I have never seen bromine water explicitly mentioned. But in the carbohydrates chapter, it is ...
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2answers
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Why oxygen is enclosed in parenthesis in some chemical reaction?

While going through my chemistry text book I came through the following reaction. $\ce{RCH2OH + (O) -> RCHO + H2O}$ In the above reaction why oxygen atom is enclosed in parenthesis ?
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2answers
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Sodium Polysulfide production from NaOH and Sulfur

Does the sulfur also oxidize the $\ce{OH-}$ radicals after the $\ce{Na2S4}$ chains form? Something like this: $$\ce{9S + 4NaOH -> 2Na2S4 + SO3 + H2O}$$
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2answers
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What are the products for the redox reaction HCl + SnCl₂ + KMnO₄?

In the redox reaction, where $\ce{HCl}$ is the excess reactant do these reactions produce following half reactions? \begin{aligned} (1)&&\ce{SnCl2 &-> Sn^{4+} + 2e-}\\ (2)&&\ce{...
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3answers
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Aqua regia and nascent chlorine

Aqua regia has the famous property of being able to dissolve noble metals, like gold and silver. I read that this has to do with the generation of nascent chlorine. How does this happen and how does ...
4
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2answers
816 views

What role does H2O2 have in copper (II) acetate formation?

Mixing solid copper, 5% vinegar, and hydrogen peroxide ($\ce{H2O2}$) causes copper acetate to form. The process will occur very slowly without hydrogen peroxide. Adding $\ce{H2O2}$ speeds the ...
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3answers
322 views

Can oxygen burn in hydrogen?

Most combustion happens involves the fuels burning in an oxidant. But there seems to be no reason that it cannot happen in the opposite way. Are there any experiments on oxygen burning in hydrogen? Or ...
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2answers
2k views

How to write the balanced equation of the reaction of potassium nitrate, carbon, and sulfur?

Given the following reaction equation: $$\ce{KNO3 + C + S -> SO2 + CO2 + N2 + K2O}$$ Here is my solution: \begin{align} & 2\times & \ce{2 N^{+V} + 2 * 5e- &-> N2^0}\\ & 5\times &...
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1answer
1k views

Flammability (NFPA) - how is it defined?

I was reading up on a wonderful little chemical compound known as chlorine trifluoride ($\ce{ClF3}$). For a primer, check out Dr. Derek Lowe's blog post here: Sand Won't Save You This Time. The title ...
18
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6answers
26k views

Why can't rust form without water?

Shouldn't iron oxide be able to form without water? It is just iron and oxygen. I don't really understand what the dot followed by the $\ce{H2O}$ means either. I was reading on wikipedia, but I have a ...
12
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2answers
4k views

What is the strongest oxidising agent?

I searched for the strongest oxidising agent and I found different results: $\ce{ClF3}$, $\ce{HArF}$, $\ce{F2}$ were among them. Many said $\ce{ClF3}$ is the most powerful as it oxidises everything, ...
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3answers
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Why can't Pd/C and H2 reduce both the alkene and carbonyl portions of α,β-unsaturated carbonyls?

Why is it that the major product of the reduction of chalcones the ketone and not the monoalcohol? In other words, Why isn't the major product a benzyl alcohol? From what I understand, catalytic ...