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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50
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4answers
360k views

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? ...
11
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1answer
3k 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 ...
14
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3answers
3k views

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 ...
22
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2answers
50k views

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 ...
11
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3answers
4k views

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{Cu + 2NO3- + 4H+ &<=> Cu^2+ + 2NO2 + 2H2O}& E &...
6
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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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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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1answer
13k views

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 ...
7
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1answer
170 views

Is there any evidence, *any evidence at all*, that nascent hydrogen actually exists?

As far as I know, nascent hydrogen is nothing more than an especially magical unicorn entity that either makes reactions happen or at least greatly facilitates reactions happening. Many years ago, it ...
4
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1answer
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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 ...
22
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2answers
5k views

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 ...
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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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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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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 ...
7
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2answers
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Why is hypochlorite a stronger oxidizing agent than other oxychlorides?

The reduction potentials of perchlorate, chlorate, chlorous acid and chlorine dioxide in acidic and basic solutions are listed in the table below: $$ \begin{array}{lcc} \hline \text{Oxychloride} & ...
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4answers
427 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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2answers
170k views

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 ...
9
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1answer
14k views

Why does KMnO4 oxidize iodide to iodine in acidic medium, whereas iodide to iodate in alkaline medium?

$\ce{KMnO4}$ should be a better oxidizing agent in acidic medium, than in alkaline medium, as per my knowledge. However, it oxidizes iodide (oxidation state = -1) to iodine (0) in acidic medium, ...
14
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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 ...
27
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1answer
48k views

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 $\...
12
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1answer
6k views

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

I learnt from a certain textbook that aldehydes and formic acid respond positively to Tollens', Fehling's, Benedict's, Schiff's and HgCl2 tests. However, in another textbook I read that even alpha-...
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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{...
13
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1answer
3k views

Purpose of ammine in Tollens' reagent

In this previous question the mechanism for the reaction of Tollens' reagent was outlined. As I understand it the oxidising agent in Tollens' is the diamminesilver(I) complex $\ce{[Ag(NH3)2]+}$ but ...
13
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2answers
607 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). ...
15
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4answers
18k views

Why is HNO3 a stronger oxidising agent than H3PO4?

Why is $\ce{HNO3}$ a stronger oxidising agent than $\ce{H3PO4}$? $\ce{N}$ and $\ce{P}$ have the same oxidation number. Is it the electronegativity difference between $\ce{N}$ and $\ce{P}$?
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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 ...
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1answer
1k 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 ...
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1answer
5k 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 $\ce{H2}$. $\ce{Fe + 2HCl -> FeCl2 + H2}$ ...
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5answers
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Electrolysis of Water

What is the mechanism for the electrolysis of water? I understand that hydrogen and oxygen gas are made, but how exactly does this happen when electrons are passed through water? A diagram would be ...
9
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2answers
34k views

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 ...
6
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1answer
20k views

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 ...
5
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1answer
1k views

Balancing by oxidation numbers method multiple atoms

In my Chemistry textbook, the rules for balancing a chemical equation using the oxidation-Number method are as follows: Assign oxidation numbers to all the atoms in the equation. Identify the atoms ...
4
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2answers
27k views

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. ...
4
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2answers
9k views

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),...
2
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2answers
500 views

Balancing a reaction where dichromate ion reacts with ethanol to give Cr(III) and carbon dioxide

I have only started to learn balancing redox reactions, and a recent question has me confused. The question is : Balance in both acidic medium and basic medium: $$\ce{Cr2O7^2- + C2H5OH -> Cr^3+ + ...
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1answer
281 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 ...
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1answer
1k views

Can an iodine clock reaction work without using a strong acid?

I'm going to do an iodine clock reaction for a project and we had to submit the materials and safety sheets for the experiment a while ago. I thought I could do one by using hydrogen peroxide, sodium ...
20
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4answers
78k views

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 ...
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2answers
22k views

Does Br2/H2O oxidize all aldehydes including carbohydrates?

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 ...
14
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1answer
9k views

Oxidation of naphthalene with KMnO4

What is the product when naphthalene is oxidized by alkaline (or acidic) solutions of $\ce{KMnO4}$? Some possible reactions show up in a google search, but they have no references: Naphthalene to ...
27
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2answers
4k views

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 ...
16
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1answer
15k views

What is the mechanism of the Clemmensen reduction?

I have learned that we can reduce a ketone to an alkane using the Clemmensen reduction, where we treat the ketone with amalgamated zinc in the presence of $\ce{HCl}$. My book didn't mention the ...
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6answers
35k 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 ...
15
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2answers
31k views

Why is nitric acid such a strong oxidizing agent?

In my teaching-lab experiments I've seen that nitric acid solutions are able to facilitate the dissolution of metals such as silver, even though they are more active than hydrogen. Does anyone know ...
15
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5answers
28k views

Do non-redox reactions exist?

Redox reaction is a type of chemical reaction, and is the result of electron transfer between chemical species. But, all chemical reactions somehow involve electron transfer! So, are there chemical ...
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3answers
14k views

Does DIBAL-H reduce carboxylic acids?

Diisobutylaluminium hydride(DIBAL-H) reduces only carboxylic acid, ester or both? The answer given was that it only reduces ester. Is it correct that under any condition carboxylic acids are not ...
11
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1answer
14k 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} $ (D) $\ce{H2SO4}$ $\...
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2answers
10k views

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 ...
4
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1answer
3k views

How does an acid prevents or discourges oxidation of iron?

In the titration of $\ce{KMnO4}$ with Mohr's salt, I have learned that sulphuric acid prevents oxidation of $\ce{Fe^2+}$ to $\ce{Fe^3+}$ in the solution before the actual titration. How does the acid ...
4
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2answers
18k views

Explanation for the reactions in a saltwater battery with zinc and copper electrodes

I am a physicist, not a chemist. I'm trying to get a basic understanding of the reactions taking place in a battery using a saltwater electrolyte with copper and zinc terminals. I'm writing a general ...

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