45

There's another question related to salt bridges on this site. The purpose of a salt bridge is not to move electrons from the electrolyte, rather it's to maintain charge balance because the electrons are moving from one-half cell to the other. The electrons flow from the anode to the cathode. The oxidation reaction that occurs at the anode generates ...


39

The anode is the electrode where the oxidation reaction \begin{align} \ce{Red -> Ox + e-} \end{align} takes place while the cathode is the electrode where the reduction reaction \begin{align} \ce{Ox + e- -> Red} \end{align} takes place. That's how cathode and anode are defined. Galvanic cell Now, in a galvanic cell the reaction proceeds without ...


38

First of all, in chemistry two types of formulas exist: structural and empirical. A structural formula shows the way atoms are connected. An empirical formula only summarizes atoms and their ratios. While often an empirical formula references a molecule, there are cases when the compound in question is not molecular, or it is unknown if it is molecular. In ...


32

Yes, cations always have a positive charge and anions always have a negative one. The difficulty is that the term cathode and anode do not always correspond to the same pole. The cathode is that pole of an electrolytic/electrochemical cell where reduction takes place (cathodic reduction) while the anode is where oxidation takes place (anodic oxidation). ...


26

Technically, even simple water can cause rust, so nothing surprising here. However, spoilage of milk most probably produced a lot of organic acids (lactic acid and similar) which can speed up any corrosion process. Lactic fermentation is a natural fermentation process in milk, when bacteria start converting the sugar content of milk to lactic acid. It is not ...


24

Water, as you may know, has a dualist nature between covalent and ionic bonding; oxygen is the second most electronegative element in the periodic table, while hydrogen's simplistic construction makes it very zen about how it forms bonds (it defines the center point of most electronegativity scales). While the bond between the hydrogens and oxygen of a water ...


22

Nitric acid corrodes copper. Drop a penny into some nitric acid (under a hood!) and you'll see that your power supplies really don't stand much of a chance in that environment. This happens with dilute nitric acid: $$\ce{3 Cu + 8 HNO3 -> 3 Cu^{2+} + 2 NO + 4 H2O + 6 NO3^{−}}$$ When you open up one of the failed power supplies, do you see bluish crusty ...


21

Long story short, no, they don't. Charging a vessel to 1 MV is not a big deal, if you look at it from the inside. To put things into perspective, imagine a vessel of about 10 cm across, which is kinda OK for a flask. Imagine it spherical to make the calculations easier. Now, the capacitance of a sphere is $C=4\pi\varepsilon_0R$, which evaluates to 5.56 pF (...


16

Well, I went and searched for the solubility of oxygen in water and oil, and found this summary paper on the NIST web site: "The Solubility of Oxygen and Ozone in Liquids" by Battino, Rettich and Tominaga, J. Phys. Chem.Ref. Data., vol 12, no. 2, 1983. Conveniently, the paper gives solubility data for oxygen in both water and olive oil. The solubility is ...


16

From what I was taught in Middle-school, cations are those ions that move towards the cathode, likewise anions are those ions which move towards the anode. Nope, the definitions are as follows (from the IUPAC Goldbook): cation A monoatomic or polyatomic species having one or more elementary charges of the proton. anion A monoatomic or ...


16

The electronic configuration has nothing to do with it. The reduction potentials of $\ce{Ni^3+}/\ce{Ni^2+}$, $\ce{Cu^3+}/\ce{Cu^2+}$ and $\ce{Zn^3+}/\ce{Zn^2+}$, if they have been/could be measured, would be even greater. The reduction potential for $\ce{M^3+}/\ce{M^2+}$ is most dependent upon the third ionisation energy. If $I_3$ is large then it will be ...


16

TL;DR The cathode in an electrolytic process is considered to be negative, so there is actually no contradiction. The cathode is a positive electrode in a galvanic cell. There are different notations for the sign ($\pm$) of the cathode used in the literature, which are determined, in particular, by the nature of the process. A very broad definition of a ...


15

The most common way to apply metals by electrodeposition to nonconductive materials is to apply a "strike" of underlying metal, usually nickel or copper, via a method like electroless plating. In electroless, the electrons for the reduction of the metal ions to the zero-valent state are supplied by a reducing agent in solution: $$ \begin{align} \ce{Red &...


14

That is because you cannot simply add the electrode potentials algebraically. In both cases, the electrode potentials have to be multiplied by $n$. What you can do instead is use Gibbs free energy change for each reaction which then can be added algebraically. $$\Delta G^\circ = -nFE^\circ$$ Using this you can get the $\Delta G^\circ$ for each reaction ...


14

The electrode at which oxidation takes place is known as the anode, while the electrode at which reduction take place is called the cathode. Reduction -> cathode Oxidation -> anode If you see galvanic cell reduction take place at the left electrode, so the left one is the cathode. Oxidation takes place at the right electrode, so the right one is ...


14

If we examine the Nernst equation: $E = E^\circ-\frac{RT}{zF}\ln Q$, the logarithmic term is what changes with concentration. The reaction quotient $Q$, gets smaller as the ratio of reactants to products increases, meaning that the log term will decrease (and become negative below $Q = 1$), so both equations will become more favourable as the ratio of ...


13

This can arise due to ion-ion interactions brought on by Coulombic fields. A proper explanation is rooted in transport phenomena. Unfortunately chemists are largely not taught this, but chemical engineers do get the opportunity. Under standard conditions, ions in a solution will take a random walk during diffusion. This results in no net movement of our ...


13

No, $\ce{CCl4}$ is not an electrolye. An electrolye is a material that causes ions (charged entities) to form in the solvent. Carbon tetrachloride neither dissociates into ions nor induces ion formation in the solvent. The reason is that the $\ce{C-Cl}$ bond is rather strong and won't break under normal solution conditions. Nor does the molecule have any ...


13

Without the salt bridge, the solution in the anode compartment would become positively charged and the solution in the cathode compartment would become negatively charged, because of the charge imbalance, the electrode reaction would quickly come to a halt. It helps to maintain the flow of electrons from the oxidation half-cell to a reduction half cell, ...


13

The purpose of the salt bridge is to prevent the two half-cell solutions from mixing. It is possible to make a really bad galvanic cell by putting both half-cells in a single solution, but they rapidly self discharge as the oxidizing agent ($\ce{Cu^+}$ in your example) can diffuse through the solution and react directly with the other electrode (Zn in the ...


13

In general, salt (particularly NaCl) will increase the rate of corrosion (rusting). To understand why, consider metallic iron $\ce{Fe}$ which rusts (oxidises) to iron(II) oxide $\ce{Fe2O3}$ in the presence of oxygen $\ce{O2}$ and water $\ce{H2O}$. $$\ce{4Fe +3O2 +6H2O->4Fe(OH)3}$$ Corrosion (rust) is a 'redox' reaction, which means it involves ...


12

Not in water. Free electron in water is really unfavorable, so no significant concentration of them can be generated chemically, and it almost immediately reduces water itself to hydrogen (but I heard rumors about generation of solvated electrons in water in very special experiment with short half-life) In liquid $\ce{NH_3}$, however, solvated electrons can ...


12

There are electrophoretic methods where the molecules stop automatically like Isoelectric Focusing, but in the common agarose gel electrophoresis of DNA you mention this is not the case. The DNA is negatively charged, it will move along the electric field you set up until you stop applying any current. It will happily move out of your gel if you let it run ...


12

Look at the unit volt. 1 volt = 1 joule per coulomb. If the number of moles is doubled, the coulombs are doubled, as is the number of joules. Think of the volt as the driving force behind an individual electron in an electrochemical system.


12

The colour of the filtrate after filtering out the solid is still lightly blue in colour. This indicates that Copper (II) sulfate still is present in the solution, meaning that there was not enough iron to completely react with all the copper (II) sulfate, visually confirming it to be the limiting reagent. A solution containing only Iron (II) sulfate is ...


11

There are two ways in which the band gap of a material: using optical spectroscopy and using electrochemistry. The way you go about analyzing the data to determine the band gap is independent of material, but the process of collecting the data is very specific to your material, and you should consult papers where others have made similar measurements on ...


11

You cannot apply the $\Delta{G}$ equation to a single electrode potential. It can be applied to a cell though so if the hydrogen electrode is connected to another electrode (say copper dipped in copper sulfate solution) then you can find the free energy. It's better to remember the formula as: $\Delta{G} = -nFE_{cell}^o$ Where $E_{cell}^o = E_{cathode}^...


10

Far from 'only now' becoming viable, the production of disinfectant from electrolysis of salt water (brine) is not only 'real' it is how bleach sold on supermarket shelves is produced! Industrially, this is called the 'chor-alkali process' and is well established for over 100 years. Both chlorine and sodium hypochlorite are manufactured industrially by ...


10

Even if the UV light idea doesn't work out very well I still want a way to do this With some photochemical background, I suggest to forget about running such a UV lamp Remember that your plasma will be formed in air. For every molecule of ozone formed, there are much more harm- and odourless $\ce{O2}$ molecules around. If you cleave $\ce{O3}$ \[\ce{O3 + ...


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