High II Chemistry Electrolytic cell with galvanic cell

Remember a mantra that works!

Rise and loss of redox agent (valency increases, is electron, is oxidized, as a reducing agent), down to reduce oxidant (valency decreases, electrons are obtained, is reduced, is made as an oxidant).

Let's talk about the electrolytic cell first, the electrolytic cell, as the name suggests, must have a power supply. That is the conversion of electrical energy into chemical energy.

The electrolytic cell is divided into anode and cathode. The positive electrode connected to the power supply is the anode; The cathode is connected to the negative pole of the power supply. This one is fixed and has nothing to do with the polar material.

The anode of the cell loses electrons, and the cathode gains electrons. The direction in which the electrons move is from the negative to the positive of the power supply. Attention! There are no electrons in the electrolyte solution, and there are ions in the solution!

Let's talk about galvanic batteries, galvanic batteries, which are batteries, and batteries are power generation. That is, chemical energy is converted into electrical energy.

The galvanic battery has no cathode and anode, only positive and negative electrodes!

The positive and negative electrodes are determined by the materials of the two poles. The negative electrode loses electrons, and the positive electrode gains electrons. The electron flow direction is also the negative electrode to the positive electrode.

Now that you know these basics, according to the mantra I mentioned earlier, some of the things that should be memorized in the tutorial book still need to be memorized, and this part mainly depends on understanding.

This should be very clear, so let's ask any questions

Hope it helps

Electrolytic cell: positive yang oxygen, negative negative also.

The direction of electron current can be summarized at one point, that is, the positive electrode is equivalent to the cathode, and the negative electrode is equivalent to the anode.

If you still have any questions, please feel free to ask.

1.First of all, judge the positive and negative electrodes, and then look at the products after judging them, and write the gain and loss of electrons first.

For example: alkaline zinc-manganese battery Total reaction formula: Zn 2mNO2 2H2O=2mNOh+2OH- The electrolyte is KOH

Negative electrode: You can write zn-2e= first, and because the product zn(oh)2 in the total reaction formula is insoluble in water, so there is zn-2e zn(oh)2 At this time, it is found that two oh- - need to be added to the reaction formula to balance, so write the negative reaction formula: zn-2e+2oh-=zn(oh).

In the same way, the positive electrode reaction: first write 2mno2 +2e- 2mnooh because the electrolyte is koh solution alkaline, so there are only two possibilities: h20 and oh- because oh- is not conserved when added, so choose h2o to get 2mno2 +2e- +2h2o =2mnooh+2oh-

I'm also studying and hope to help you-. -

1.For such a dilute HCl solution, the H+ ionized by the water itself is not negligible. In fact, at this time, the H+ in the solution is basically ionized by water.

The specific calculation method is: total C(H+) in solution = C(H+) ionized by HCL + C(H+) ionized by water

The former = 10 -13 and the latter = c(oh-) in solution, because the amount of H+ and Oh- ionized by water is always the same.

Therefore, the equation c(h+)=10 -13+c(oh-) is obtained, and combined with the ionic product formula of water, the equation can be solved to obtain c(h+), which is very close to 10 -7 numerically. That is, at this point the solution pH = 7

2.The characteristic of galvanic cells is that the oxidation reaction and the reduction reaction occur in different places. In copper-zinc galvanic cells, Zn is oxidized into Zn2+ into solution. Cu2+ is reduced to Cu and precipitated from solution.

Essentially, the galvanic cell reaction can occur when Zn is inserted in any solution, and it can also be inserted in CuSO4. However, direct contact between Zn and CuSO4 solution will cause a direct displacement reaction, which interferes with the galvanic cell reaction and consumes energy, so it is generally not done.

3.Theoretically, the concentration of the electrolyte is constant, and the cathode is precipitated as much as the anode is dissolved. However, in practice, there are always some impurities in the Cu of the anode, such as Fe, etc., which are more active than Cu, and they will not precipitate at the anode after they are dissolved into the solution, but will be replaced by the precipitation of Cu2+ in the solution.

The unit mass of these impurities is smaller than that of Cu, so the amount of anode dissolution (including Cu and these impurities) will always be less than the amount of cathodic precipitation during actual electrolysis, and the concentration of CuSO4 in the electrolyte will also decrease slightly.

The two poles of the galvanic battery are called the positive and negative electrodes, and the negative electrodes lose electrons; The electrolytic cell is called the cathode, with an external power supply, and the power supply is facing the anode (loss of electrons).

The principle of galvanic cells is redox reaction, where the anode undergoes an oxidation reaction and the cathode undergoes a reduction reaction. Therefore, you should first know what the reaction principle is.

The main points are as follows: 1) The oxidation reaction occurs at the anode, and the reduction reaction occurs at the cathode, and the positive electrode connected to the anode is the negative electrode.

2) When writing the electrode reaction formula, first write the pole that you think is correct and simple, and then subtract it from the total reaction formula.

3) Pay attention to the acidity and alkalinity of the reaction environment. For example, in an acidic environment, no hydroxide can appear, and no hydrogen ions can appear in an alkaline environment.

Typical examples are: 2H2O+4E-+O2=4OH- (alkaline environment) 4H++4E-+O2=2H2O (acidic environment).

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.

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.

1.If there is a power supply, the electrolytic cell is the battery, and if there is no power supply, the galvanic battery. Of course, that can only be judged if the conditions are met. Figure A belongs to fuel cells (galvanic batteries).

2.There is KOH in the total reaction formula, but the actual redox reaction is still methanol and oxygen, so you use 2CH3OH+3O2=2CO2+4H2O minus 3O2+6H2O+12E-=12OH- to get CH3OH+6OH--6E-=CO2+5H2O.The judgment can be thought of like this:

The pH before and after the reaction of the total reaction (methanol and oxygen) is unchanged, that is, it must remain neutral, but the positive electrode water and oxygen get electrons to form OH-, and the pH increases, in order to maintain pH = 7, then OH- must be consumed at the negative electrode. As for KOH, it's just an electrolyte, and if it's an acid, it doesn't react, but it happens to be a base, a base that reacts with the CO2 generated, but it doesn't participate in the actual "redox reaction".

3.Your question is why the cathode doesn't turn H+ into H2 and run away. That's because if H+ all becomes H2 and runs away, OH- will also combine with Mg2+ to form a precipitate, then chloride ions will be left in the solution and become a negatively charged solution, but the solution always has to remain electrically neutral, so only when water gets the OH- combined with Mg2+ generated by electrons to form a precipitate, the electrical property of the solution can remain neutral.

Pool A belongs to the galvanic battery, which is equivalent to the power supply of other pools, and the alkaline environment is OH-discharged, if it is generated by water, it will also react with OH-, because the existence of Mg2 2 H20=Mg(OH)2 2H Only the generation of hydroxide is in line with the actual situation

Because the medium of the first pool is KOH, if it is water, the hydrogen ions generated will react with hydroxides.

The electrolytic cell is equivalent to the electrical appliance, and the galvanic battery is equivalent to the power supply

Part of the rechargeable battery is the principle of the electrolytic cell when charging, and the galvanic battery when discharging

Quite simply, the cathode withdraws electrons and the anode discharges. According to the strength of the electronic ability of the metal, the key is to see what metal the cathode is and what metal the anode is

Galvanic cells are put in a solution of soluble acids.

The metal in front of h is used as the negative electrode.

The metal behind h is used as the positive electrode.

Electrons flow from the negative electrode to the positive electrode in the solution to form an electric current.

Your concept is confusing.

First of all, in the galvanic cell, the electrons lost at the negative electrode are oxidized, and the electrons obtained at the positive electrode are reduced.

1 The negative electrode is zinc losing electrons.

2 Metals do not gain electrons with negative valence, so aluminum only loses electrons, so the positive electrode hydrogen ions gain electrons.

3 Positive electrode 2H + 2E = H2 Here hydrogen ions are consumed, so sulfuric acid is consumed.

Negative zn-2e = zn2+

4 Hydrogen ions come from water, and mg does not react with sodium hydroxide. 2al+2naoh+2h2o=2naalo2+3h2↑

1.In the Zn Cu galvanic cell, because the activity of Zn is greater than that of Cu, Zn is used as the negative electrode, and the reaction formula is Zn-2E-=Zn2+

2. Because Al will be passivated with sulfuric acid, magnesium is used as the negative electrode to lose electrons, because the positive electrode is electrons combined with hydrogen ions to generate hydrogen.

3.Positive electrode: 2H++2E-=H2 Negative electrode: Zn-2E-=Zn2+ The H+ in the positive electrode comes from the ionization of sulfuric acid, so it will consume sulfuric acid.

4.Ionization from water.

What is the use of the salt bridge in the galvanic cell device: the main function is to transport anions or cations (the directional movement of ions in solution, i.e., conduction).

How is the method of transporting ions inside: first determine the positive and negative electrodes in the galvanic cell device (the metal with strong reducibility is the negative electrode), and then draw the direction of movement of the electrons (the negative electrode flows out of the electrons, and the positive electrode flows into the electrons), and the direction of movement of the electrons (negatively charged) is also drawn in the solution (there are no electrons in the solution, so the anion is equal to the direction of movement of the electrons, that is, the anion flows to the negative electrode; The cation is equal to the opposite direction of the direction of motion of the electron, i.e. the cation flows to the positive electrode).

The salt bridge connects two separate electrolyte solutions into a single unit, forming a closed loop, and the redox reaction can occur.