High School Chemical Electrolysis and Galvanic Cell Problems! Seek superiority

The electrode reaction formula in the first cell is:

Anode: 2H2O-4E-==O2+4H+

Cathode: 2cu2+ +4e-==2cu

The correspondence between the transfer of electrons and the formation of gas is 4e- o2, and when 1mol of electrons pass through the circuit, the oxygen produced is .

The electrode reaction formula in cell B is:

Negative electrode: mg-2e-==mg2+

Positive electrode: 2h+ +2e-==h2

The correspondence between the transfer electrons and the gas gas is 2e- h2, and when 1mol of electrons passes through the circuit, the hydrogen gas produced is.

So the volume of gases produced is not equal.

A-pool cathode: 2cu2+ +4e- ==2cu anode: 4oh- -4e- ==2h2o + o2 b-pool anode: al-3e- ==al3+

Cathode: 4cl- -4e- ==2cl2

So the volume of the gas produced is not equal.

First of all, let's talk about galvanic cells, galvanic cells are magnesium that loses electrons to become magnesium ions, and electrons react with aluminum rods and hydrogen ions in the solution to generate hydrogen, and 1mol electrons can generate hydrogen.

Then there is the electrolytic cell, the electrolytic cell is the electrolysis of copper sulfate solution, copper ions gain electrons to generate copper, and water loses electrons to generate oxygen and hydrogen ions, 1mol electrons can generate oxygen.

So the volume of gas produced in the end is not equal.

If you have any questions, you can ask, hope.

The galvanic battery is corroded by oxygen absorption, zinc loses electrons as the negative electrode, and carbon does not react with the positive electrode, so it can only be oxygen and water to obtain electrons to generate hydroxide.

The cations in the electrolytic cell only have hydrogen ions and sodium ions, and hydrogen ions are more active than sodium ions, so hydrogen ions get electrons to generate hydrogen, while anions have hydroxide and chloride ions, chloride ions are more active than hydroxides, and electrons are generated into chlorine.

As for oxygen in sodium chloride solution, it is oxygen in the air that is dissolved in the solution.

This galvanic cell is an oxygen-absorbing corrosion reaction, and the ions in the electrolytic cell are only chloride and hydrogen, so the electrons are hydrogen, and the electrons are chlorine.

Galvanic cells:

The principle of galvanic cells is a redox reaction that can be carried out spontaneously.

Generally, the active ones do the negative electrode, and the poor ones do the positive electrode, and there are some reactions that you have not seen, such as the reactant ni, Ni(OH)2, and the product niooh This battery reaction, which is a rechargeable battery, analyzes the valence, nickel 0 valence, nickel in nickel hydroxide +4 valence, nickel in nickel hydroxide is +3 valence, so it is nickel electron loss, do negative electrode, nickel hydroxide electron, do positive electrode.

Electrolytic cell: The most important point is to remember that the electrode of the cathode will not react, even if it is more active than the electrode of the anode, the anode is connected to the positive electrode of the galvanic battery, and the oxidation reaction occurs, first of all, look at the activity of the electrode, the metal before AG does the anode, and the anode metal loses electrons, including silver, taking Cu as an example, Cu does the anode, and water does the electrolyte, the essence of electrolysis is Cu discharge to generate Cu ions, hydrogen ions in water are discharged to generate hydrogen, and the remaining hydroxide is combined with Cu ions to form copper hydroxide.

Cu + 2H20 = (energized) Cu (OH) 2 + H2 (gas symbol) except when mg is used as an electrode.

For example, although Al is not as active as MG NaOH, MG itself does not react with sodium hydroxide, so Al discharge is the equation for the reaction between Al and NaOH.

If you don't understand, ask me again (we're both juniors in high school).

Looking at the electrode, it is also necessary to see how easy it is for ions to gain and lose electrons.

Now that you know the direction in which electrons are gained and lost, the next step should be to determine the positive and negative electrodes (or cathodes) and write the electrode reaction equation.

According to the direction of the electrons gained and lost. You can determine what kind of substance is happening when the oxidation reaction occurs over there and the reduction reaction occurs there, and you can judge what reaction occurs by looking at the valency of the substance.

Look at what substances are contained in each of the two electrodes, and compare the activity of the substances contained in each electrode, that is, the ability to gain and lose electrons, that is, to determine which is the reactive substance!

You know what you gain and lose, you don't know who gains and who loses, look at the valence rise.

That is, first you have to know which two substances will undergo redox reactions. It's those two substances.

Theoretically, an electrode potential can be formed between the different valence states of any element, so any two pairs of pairs combined together are a battery. However, if you use it as a battery, you must also consider whether the potential difference is appropriate, whether the electrode reaction speed is fast enough, and so on.

Then Cu can form an electrode as long as it is placed in his solution, and the same is true for silver, so as long as there are elements in the solution with their different valences, it is not necessary to be a nitrate solution.

Why does cu lose electrons, this is related to the essence of electrochemical reactions, it has been said in the second paragraph, different valence states can form electrodes, this is because the free electron (relative to the distance of the nucleus in the molecule can be considered infinite) electric potential energy is 0, which is high school physics knowledge. Then the electron is bound by the nucleus, and the energy must not be 0 if it becomes a valence electron, because it is in the electric field of the nucleus at this time, and at the same time causes the energy of the system to decrease (because when the electron is not far away, the energy is negative), then the number of charges carried by different nuclei is different, and the orbital (distance from the nucleus) is also different, so the degree of reduction of the energy of the system is different.

So, if you think about it, if you connect an electrical appliance or a wire to an external circuit (both of which have the effect of connecting two electrode systems), the electrons will run from the low-energy system to the higher direction, because the electrons are negative energy units. It can be seen that if you do not use silver, change to a system with lower energy than cu, such as zn, then zn will lose electrons.

If you're already in college, look at the theory of molecular orbitals, and in addition, it involves solvation, electrode equilibrium, Nernst equations, etc.

Copper metal is lively, so it loses electrons, and it is not possible to exchange the solution, because silver ions can only be reduced on the silver rod, not on the salt bridge.

Copper is more active than silver, and the active metal loses electrons as a negative electrode.

The choice of salt bridge: 1The ions do not participate in the electrode reaction, and the inert ions of the electrochemical reaction are the best.

2.The ion mobility is high (good for electron conduction), so it is best to choose monovalent alkali metals and halogens;

3.The solution should be saturated so that the conductivity efficiency can be maximized.

Selection of solutions on both sides of the salt bridge in galvanic cells: The electrolyte solution corresponding to the electrode should be selected, which can not only react, but also reduce potential loss.

The battery consists of two half-cells, which undergo oxidation and reduction reactions respectively, and are connected by a salt bridge (equivalent to a separator) on the inside, and electrons are transferred by a conductor on the outside, converting chemical energy into electrical energy. The Cu i Cu++ half-cell produces a stable electrode potential, and the Ag+ i ag produces another stable electrode potential, which is stable because the ion concentration is stable. If Cu is immersed in AgNO3 solution, it is equivalent to the formation of many microbatteries, which cannot produce macroscopic unified electron transfer, which is equivalent to a short circuit inside the battery, and there is no external current generation, only the displacement reaction is exothermic at the same time, and the chemical energy cannot be converted into electrical energy.

Cu is more active than Ag, Cu loses electrons and is oxidized, and Ag+ electrons are reduced.

(1) When charging, you can understand that the galvanic battery becomes an electrolytic cell, so the negative electrode of the galvanic battery (which becomes the cathode of the electrolytic cell) is connected to the negative electrode of the power supply. Anodizing, loss of electrons, note that the alkaline environment 4(OH)-4E- = O2 + 2H2O

2) As a galvanic cell, the negative electrode undergoes an oxidation reaction and loses electrons, note that it is an alkaline environment CH3OH-6E- +8 (OH)- = (CO3)2- +6H2O

3) Kneel and beg for the total reaction of the nail pool.

4）2ch3oh （l）+ 3 o2(g) = 2co2(g) +4 h2o（l）△h（298k）=—

The cathode material of zinc-manganese battery is manganese dioxide powder, and the electrode reaction is carried out on its surface, and the tetravalent manganese is electronically reduced to trivalent manganese.

It is said: "The reaction process is that the protons of the liquid phase pass through the interface of the two phases, enter the manganese dioxide lattice and combine with the negative divalent oxygen to form hydroxide ions, and the oxygen in the original manganese dioxide lattice is replaced by hydroxide ions." This water manganese stone is formed directly in the manganese dioxide lattice. ”

The primary response is:

mno2 +h^+ e^- ==mnooh

In alkaline solution:

mno2 +h2o +e^- ==mnooh +oh^-

In the presence of ammonium chloride solution:

mno2 +nh4cl +e^- ==mnooh +nh3 +cl^-

Due to the limited level of knowledge, I can only understand that the electrons of Mno2 must form OH - and H+ is required, so in the absence of H+, "hydrogen ions ionized from a weak electrolyte (such as H2O) are used to make do".

If it goes deeper, it's probably the issue of scientists......

ps: Ignorant and unheard, although I really want to help you, but I may not be able to help you.

PS again: I also have the habit of struggling with some non-test point knowledge and getting to the bottom of it, and today I can be regarded as seeing the same kind! It's a pity that I didn't understand this problem much when I learned it before......So I can't help, these are to help you ask and check.

I hope you will get through the relevant knowledge of primary batteries as soon as possible!

In a battery, the positive electrode gains electrons, and the negative electrode loses electrons. Water as an electrolyte. The specific reason for generating the latter thing, the knowledge in high school is not easy to explain, just remember it (it is alkaline near the positive electrode, so it is represented by oh-).

You are wrong, in galvanic cells, the negative electrode is the pole where electrons are lost by the relatively active metal, and the positive electrode is the pole where electrons flow in.

The negative electrode is Fe, the positive electrode is Cu, and the electrolyte solution is NaCl solution. The two electrodes (two electrodes with different activity) and one liquid (electrolyte solution) close the loop, and there is a redox reaction that proceeds spontaneously.

The example you gave is not a spontaneous redox reaction, which means that one of the iron and copper cannot react directly with the sodium chloride solution.

To give you an example, replace sodium chloride with sulfuric acid.

Negative electrode: Fe-2E-=Fe2+

Positive electrode: 2h+ +2e-==h2

How are the reactants selected for the cathode reaction? In what order?

Generally, cathode materials do not directly obtain electrons, there are ions in the solution, and the electrons with strong oxidation ability are obtained first. In addition, the addition of the positive and negative electrode reactions gives a redox reaction that can be carried out spontaneously, which is Fe+2H+=H2+Fe2+

The negative electrode loses electrons; The positive electrode gets electrons.

The one with strong reduction loses electrons first; The one with strong oxidation gets electrons first.

Your example is not a galvanic battery.

The negative electrode is Fe, the positive electrode is Cu, and the electrolyte solution is NaCl solution, which cannot be formed into a galvanic cell because the redox reaction cannot occur.

First of all, the negative electrode is electron-loss, the positive electrode gains electrons, the negative electrode is generally a reactive metal, such as Fe loses electrons, forming Fe2+, and the positive electrode is the cation in the solution where electrons are obtained, which are reduced to metal elementals, if the negative electrode is Fe, the positive electrode is Cu, and the electrolyte solution is CuCl2 solution, then the Cu2+ in the solution gets electrons at the positive electrode, generating Cu elemental, and the negative electrode reaction: Fe-2E- =Fe2+

Positive reaction: Cu2+ +2E- =Cu

The total reaction equation is: Fe + Cu2+ = Fe2+ + Cu

To determine whether it is a galvanic battery, first look at whether the redox reaction can occur between the positive and negative electrodes and the electrolyte solution