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Questions tagged [electrochemistry]

The branch of chemistry that deals with the study of redox reactions and how they can be applied to generate electricity (in electrochemical cells) and to carry out non-spontaneous reactions using electricity (electrolysis).

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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? ...
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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 &...
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Positive or Negative Anode/Cathode in Electrolytic/Galvanic Cell

In a galvanic (voltaic) cell, the anode is considered negative and the cathode is considered positive. This seems reasonable as the anode is the source of electrons and cathode is where the electrons ...
3
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1answer
2k views

Why Co3+/Co2+ couple have high reduction potential?

Cobalt is changing from 3d6 to 3d7 electronic configuration. What's so stabilizing about that? Just by reduction potentials this couple is more oxidising than hydrogen peroxide and that just sounds ...
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5answers
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Why don't the electrons move through the electrolyte (instead of the circuit) in a galvanic cell?

I was learning about galvanic cells and I had a problem understanding why electrons do not travel through the electrolyte solutions themselves, instead preferring to travel through metals. Can ...
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1answer
1k views

Deriving a reduction potential from two other reduction potentials

Given: \begin{align} \ce{Co^{3+}(aq) + e- &-> Co^{2+}(aq)} & E° &= \pu{+1.82 V} \\ \ce{Co^{2+}(aq) + 2e- &-> Co(s)} & E° &= \pu{-0.28 V} \end{align} ...
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1answer
4k views

How can there be decimal subscripts in a molecular formula?

While learning about how batteries work I have encountered the following notation for a Li-ion cathode: $\ce{Li_{0.5}FePO4}$.[1] According to Wikipedia, the subscript number in a reaction equation ...
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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 ...
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3answers
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Difficulties understanding how salt bridge works

A picture for reference: Difficulty 1: I don't get why a salt bridge is needed. People say it's to maintain the overall neutrality. But in both cases where salt bridge is a tube of solution and a ...
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3answers
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Why the salts in a salt bridge?

Take the example of a copper and zinc galvanic cell, connected by a salt bridge of $\ce{KNO3}$. I understand how the reactions will result in positive and negative charges, and that the ions of the ...
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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 ...
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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{...
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2answers
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Is there always a need for a salt bridge to let a galvanic cell work continuously?

I read in a book that "Sometimes, both the electrodes dip in the same electrolyte solution & in such cases we do not require a salt bridge". How is this possible?
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2answers
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Conducting current in electrolytes

I keep trying to figure out how current is conducted through an electrolyte but all I can find are BS half answers. They say the ions conduct, but the specifics are poorly explained or absent. I ...
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1answer
114 views

What is the composition of the oil-like fluid that seeps out of dry-cells over time?

An experience a lot of us might've had; a dry cell (not completely depleted) when left in an electrical device for long periods of time, has this viscous fluid coming out that usually corrodes the ...
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1answer
895 views

Why does the anode solution contain Sn2+ in a Sn-Cu voltaic cell?

Suppose you have the following voltaic cell: $\ce{Sn_{(s)}|Sn^{2+}_{(aq, 1.0 M)}||Cu^{2+}_{(aq, 1.0 M)}|Cu_{(s)}}$ and the salt bridge is $\ce{KNO_3}$. What I don't understand is why you need to have $...
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2answers
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What causes electrons to move from zinc to copper?

Here is something that no video in youtube about electrochemistry can explain me about galvanic cells. Suppose we have $\ce{Zn}$ metal immerse in $\ce{Zn^{2+}}$ in one side, then $\ce{Cu}$ metal ...
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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 ...
2
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1answer
1k views

Does the relationship equation between standard cell potential and equilibrium constant violate potential's intensive properties?

The equation: $$E^{。}_{cell}= \frac{RT}{nF}\ln K_{eq}$$ We all know cell potential is intensive, not affected by the amount, Because: $volt=\frac{joule}{coulomb}$. Both joule and coulomb will be ...
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4answers
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Determining the order of molar conductivity

This was a question which came in a objective type examination. Which of the following have a $\lambda^\infty$ (molar conductivity at infinite dilution) larger than $\ce{KCl}$? A. $\ce{CH3COOH}...
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0answers
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What can explain the more weight gain of aluminum coated steel than non-coated steel after NaCl immersion?

I have a 2 week experiment. I put aluminum coated and non-coated steel of the same size and shape in separate beakers with NaCl solution. Both are sealed. But, I am surprised that Al coated steel ...
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2answers
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Why do acids favor the oxidizer? And bases the reducer?

Simply put, why does adding acid to the cathode up the cell voltage? From what I understand, acids are proton donors. Do these positive protons attract electrons toward the cathode compartment of the ...
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1answer
8k views

Standard Hydrogen Electrode

Could someone, please, explain to me how the standard Hydrogen Electrode works and how it is used to measure electrode potentials? Also, why does it have a potential value of zero?
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1answer
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Does the chemical in an alkaline battery make battery leaks unavoidable?

Battery leaks was an issue in the 80s and 90s, and since quality and innovation is constantly improving, I thought battery leak might be slowly going away. But I found that even nowadays, name brand ...
15
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1answer
382 views

How does conductivity work for non-redoxed ions?

Related (very similar, but here I want a mechanism) https://physics.stackexchange.com/q/21827/7433 By the Kohlrausch law, all ions contribute to the conductivity of an electrolyte. Now, as I ...
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1answer
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If electrolysis splits water, why does only either hydrogen or oxygen (but not both) bubble up on one pole?

If electrolysis splits water, then that means that $\ce{H2O}$ is split into $\ce{H}$ and $\ce{OH}$ or $\ce{O}$. How come that if a water molecule is split at e.g. the negative pole (anode), only the ...
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2answers
225 views

Decreasing magnitude of peaks in cyclic voltammogram?

I'm in an instrumentation course and we covered cyclic voltammetry earlier in the semester and will be doing an experiment in CV next week. My question is this: If you have a reaction and sweep the ...
3
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2answers
739 views

Why is current non-zero when applied potential is still below E$^0$ in cyclic voltammetry?

In this diagram (Evans et al., J. Chem. Edu.) the current is non-zero, but the potential is still below the normal potential. How can the compound become oxidized at the working electrode, when the ...
3
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2answers
10k views

Derivation of relationship between Gibbs free energy and electrochemical cell potential

Why is $\Delta G=-nFE?$ I don't understand what the motivation is behind this definition. Was it derived or just given? The textbook provides no justification for this equation. In fact, much of the ...
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1answer
252 views

Glass electrode pH measurement

How is the potential difference between the outer and inner surface of the glass bubble in a glass electrode measured if an Ag/AgCl wire is used as the indicator electrode and Ag/AgCl/KCl is used as ...
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1answer
584 views

Does it matter what electrolyte we use for a Galvanic Cell?

A typical Galvanic Cell, say a Daniell cell, consitsts of two separate beaker, one containing Zn rod dipped inside aq $\ce{ZnSO4}$ and the other beaker containing Cu rod dipped inside $\ce{CuSO4}$. ...
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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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How do I determine whether it is the *ferrous* or *ferric* ion that is implied in this displacement reaction?

I'm supposed to write a balanced equation for: $$\ce{Iron(s) + copper(II) sulfate(aq) -> ?}$$ If I use Iron(II)/ferrous I get $$\ce{Fe + CuSO4 -> FeSO4 + Cu}$$ and if I use Iron(III)/ferric, ...
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1answer
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Does concentration of salt increase or decrease rate of rusting?

I want to know whether increasing the concentration of salt, specifically $\ce{NaCl}$, increases or decreases the rate of rusting. There are conflicting theories that explain opposite outcomes: ...
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3answers
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Electronegativity of zinc vs copper in galvanic cell

I am reading up on how galvanic cell works and I realised that the flow of electrons is from Zn to Cu. But Zn is more electronegative compared to Cu according to periodic table trends I read it ...
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2answers
7k views

Correct equation for Ionic Conductivity (λ) in Solutions?

We haven't started on Electrochemistry at school yet, but I did manage to find some time to read up on the topic. One thing I've noticed from when I started, is that different books and sites use ...
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2answers
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Why do electrons follow from Zn to Cu but not Cu to Zn in the lemon battery experiment?

In the lemon battery experiment, as I understand, both $\ce{Zn}$ and $\ce{Cu}$ meet acid in the lemon, cause $\ce{Zn}$ and $\ce{Cu}$ release electrons to form $\ce{Zn^{2+}}$ and $\ce{Cu^{2+}}$. So ...
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1answer
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How can I produce hydrogen gas efficiently and cheaply?

I have been intrigued by one of the principles of chemistry lately- electrolysis. In my knowledge, electrolysis is a quite dangerous operation as the decomposition of water produces hydrogen and ...
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2answers
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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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2answers
333 views

Is it possible to have electric field in water without having electrolysis?

Is it possible to have electric field in water (using electrodes with voltage difference) without having electrolysis in the water (or any other reaction)?
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1answer
692 views

Electronegativity

Why is the Electronegativity difference for atoms in bonding uncertain while determining what the compound will be? According to the IB(International Baccalaureate) they say that the ...
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2answers
501 views

Why does copper form bubbles in vinegar in this situation?

I watched this video in which the host tries to show the principles behind the voltaic pile. The host first immersed zinc in vinegar and bubbles are observed forming around zinc. I've learned that ...
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3answers
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Is it dangerous to inhale the steam coming from electrolysis of salt-water solution

Is chlorine in there that accumulates (at the anode) and emerge out as chlorine gas? I was worried since I added a pinch of salt to the steamer in order to hasten the heating of tap water when I ...
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1answer
4k views

Reaction of sulfate ion in copper sulfate electrolysis

I am planning to try copper plating a piece of metal by performing electrolysis on an aqueous solution of copper sulfate. I plan run an electrical current with the metal I want to plate as the cathode ...
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3answers
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Hydrogen fuel cell - why do the H+ ions move through the electrolyte

Consider the following hydrogen fuel cell http://butane.chem.uiuc.edu/pshapley/Enlist/Labs/FuelCellLab/FuelCell.html At the anode, hydrogen is oxidised (losing electrons). My first question is this: ...
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Effect of concentration on molar conductance

It has been stated that the molar conductance($\Lambda_m$) of strong electrolytes is not affected to a greater extent on dilution and so to find the limiting value of molar concentration($\Lambda_m^0$)...
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542 views

Single electrode potential measurement

My textbook says that in a galvanic cell, it's not possible to measure single electrode potential independently. Instead, a Standard Hydrogen Electrode is used as the system is under equilibrium. Can ...
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1answer
4k views

What is the Purpose of an Electrolyte in a Galvanic Cell?

I understand how a galvanic cell works and the purpose of erverything such as the ssalt bridge and the electrodes, however I don't understand why an electrolyte is required. For example, consider this ...
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2answers
489 views

How is the standard electrode potential measured without allowing the electrolyte concentrations to change?

Let's say we need to measure the standard electrode potential of a zinc electrode dipped in an aqueous solution of $\ce{ZnSO4}$. To do this, we use the standard hydrogen electrode(SHE)-the reference ...
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1answer
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While electrolyzing concentrated aqueous sodium chloride, why is it that chlorine is discharged but not sodium?

Hydrogen and hydroxide both exceed sodium and chlorine in terms of reduction and oxidation potential respectively. While electrolyzing a concentrated solution of aqueous NaCl, it is known that ...