The sudden chemistry of Electrolysis

The sudden chemistry of Electrolysis 

We all know that a piece of metal conducts electricity well. And we also know we should not touch the metal if it conducts high amount of electricity. So how does this really happen? The basic types of bonds in chemistry are as two types as primary and secondary. The primary bonds are then categorized into 3 parts called Covalent, Ionic and Metallic bindings. Here, a metallic binding between the metal atoms in the piece have free river of electrons floating in. Now, the extra flow of electrons by the electric current can use these atoms as their medium to move (We’ve sent a separate article for the bindings, see it first). What’s really happening is this flow of electrons.

Actually how do they make these rivers of electrons? This is how it happens; an atom should always be in a neutral charge to equally share their number of electrons which are negatively charged and the number of protons which are positive. For a metallic atom like for an example aluminum removes its electrons in the ground state and makes a full river of it. While a removed electron is negative, the charge of the atom or now it is an ion is positive. So they tend to conduct electricity.

But it doesn't say that only metallic bonds can conduct electricity. It is fair to say that covalent bonds are not that good conductors because of their loosen properties such as their weak binding. But ionic bonds in case are very good conductors in aqueous or molted media. This is because an ionic bond is a very strong bond in a lattice structure in solid medium. So in their solid medium, they can't conduct electrons because they are not free of their lattice structures. 

They become extremely complex in a liquid or soluted occasions. For an example NaCl which is salt, conduct electrons well when it's dissolved in water. An ionic bond is made up from a metal and a non-metal binding each other. You've learned that a bond is made removing an electron by a metal and by the absorption of it by a non-metal. 

As shown in the picture, they both have 2 electrons in the first electron circle (we call it a cell). And 8 electrons in the second cell. But in the third cell, they have 2 different numbers of electrons. But in general, for it to be stable like other 2 cells, there has to be 8 electrons. For Sodium (Na), there is only one electron, nut there has to be 8 electrons and which means, it needs 7 more. But finding 7 electrons is definitely not easy. So instead of taking an electron, it removes one and cancel the third cell. But chlorine in fact is the inverse. It has 7 electrons and which means it needs one more. So as sodium removes one, Cl takes it and make a full stable cell. 

But there happens a strange case. The nucleus (Red region) of the sodium atom is +11 charged. And the electrons are -11 charged. So +11+(-11)=0. But when it removes one electron, the negative charge become -10. Then, 11-10=+1. So when it removes the electron, it charges to +1, so we call it a positive ion or a cation.

The direct opposite happens to poor Chlorine. It generally has +17 in the nucleus and -17 charge in the electrons. So its 0. But as it takes one electron, it becomes -18. So 17-18=-1. So we call it a negative ion or an anion.

So the Sodium cation is +1 charged and Chlorine anion is -1 charged. but when the compound forms, they get together and 1-1=0 and become chargeless. And notice that sodium which is a metal has taken the positive charge while chlorine, the non- metal has taken the negative one. So in theory, metals are mostly cations and non-metals are anions. 

These salts stay in very hard crystalline forms as above, but they easily dissolve in water. The best example is salt. When they dissolve, their normal NaCl type breaks and separate into ions. So when they are aqueous, their normal form is Na+ and Cl-. We know that water is made from hydrogen and oxygen, H2O. Which means there are 2 hydrogens and one oxygen. When the salt is dissolved in water, water too divide into pieces, H+ and OH-. OH- in case is made from 2 elements. But it is negatively charged as the H+ cation is positive. 

Now think there is a salt solution as below. 2 terminals, + and - are connected from a battery pack (almost 12V). We have used carbon rods as the terminals because in the mean process, some reactions could occur and if we use metals such as a piece of iron, it will react and add neighbour substances.

As shown in the above diagram, the flow of electron always happens from negative to positive. So the negative terminal give off electrons while positive terminal takes electrons.
The Sodium and the Hydrogen ions are + charged, so they should take an electron to be normal so they go and take one from the negative terminal. And the Hydroxide (OH) ions and chlorine ions which are negatively charged move to positive terminal to get rid of the electron. As 2 of the chlorine ions remove a electrons, it transmit to Cl2 gas (Shown in yellow). And so on oppositely, 2 of the hydrogens get used buy some electrons and free up being H2 gas. 

2(H+) + 2(e-) = H2
2(Cl-) = Cl2 + 2(e-)

So each product of chlorine and hydrogen come out of each + and - electrode respectively. But there is something remaining. The remaining OH ion can not turn into a gas of H2O2 (Hydrogen peroxide) as well as the Na. Sodium is generally a metal, and not a gas and because of its extremely high reactivity, the emerging Na reacts directly with OH and make NaOH Sodium hydroxide. We can once test the product of it as because NaOH is a strong base, it can turn an indicator to a base colour. Sure we can make this wonderful compound at home with a battery and some salt, but the problem is in case, the Cl2 gas emitted will not be 100% and some of the Cl2 gas can re dissolve in the water and make it acidic a little. So when chlorine reacts with water, it forms HCl (Hydrochloric acid) and HClO (Hypochlorous acid) and it will react with NaOH to remake NaCl and a bit of bleach (NaClO). We can test it using an indicator. 

The acid base indicator Blue pea ('Katarolu') doesn't indicate any colour with a NaCl solution because it is neutral.

But when the current is passing through the solution, the negative side of it turns green indicating it is basic and the positive terminal side turns colourless and pink a little. This is happening because Cl2 dissolves in water making it acidic. But with this indicator, an acid should be brightly pink, but in case HClO Hypochlorous acid is strong enough to crunch the colour of it. The slight pink is due to HCl.

But the yield of acid is not as 100% as NaOH. Because some Cl2 escape, the solution is considerably basic. Now what happens is that at the - terminal, H2 releases keeping OH alone so it binds with Na to form Sodium hydroxide. Even though there are some Cl- ions in the green basic region, it turns into the new colour because of the presence of the OH. That means, it's not the sodium that is showing the basic feature but the OH- group. But for many specialities of sodium, the compound turns out to be exaggeratedly basic. Both of the parts are separated from a regiform sheet which allows the two liquids to not pass each other reacting. But if we mix them each other, they will still show a light green colour because of the more NaOH yield.

 What do you think if we electrolyse the NaOH solution more on? The NaOH re ionize to Na+ and OH-. As well as water to H+ and OH-. Then we are going to have 2 OH- groups. 2H+ just go off the negative terminal remaining the others. 2OH- becomes H2O2- as Hydrogen peroxide. One of its Oxygen, O- removes off to positive side leaving H2O. Now we have O2 gas in the positive side instead chlorine. H2O and Na reacts to form NaOH and H again. We then get another H atom at the - terminal. So 2 H2 goes of from negative and one O2 goes from positive terminal retaining NaOH. So it means that breaks water into H2O. But the basic property doesn't change.

Sometimes if we electrolyze a salt like CuSO4 Copper sulfate, we get pure Cu copper metal out from one electrode. 

The copper metal in this case removes 2 electrons to make copper sulfate. SO4 sulfate is an anion formed by sulfur and oxygen and they act as a single compound like OH hydroxide. So when ionizing, they become Cu 2+ and (SO4) 2-. Copper in this case goes to negative side leading its powder coming out of the electrode. Sulfate SO4 cannot divide into sulfur and oxygen as OH did into oxygen and hydrogen. So it keeps trapped. OH then turns to Oxide and Hydrogen ions, O 2- and H+, notice that oxygen is 2- charged. O2 gas then come out from + electrode while H2 comes from - electrode. Notice that both copper and hydrogen come from - side. What remains is H+ and (SO4) 2-. They both come out and make H2SO4. H has to be doubled because +1-2=-1 as the positive terms doubles, +2-2=0. Now H2SO4 is Sulfuric acid. So in this method, we have created an excellent acid. And you can also try this at home. Why that copper is removed is that copper does not react with acids, so it makes pure copper metal. This is because as copper is the cation in CuSO4 and hydrogen in H2SO4. Hydrogen is more reactive than copper so hydrogen takes its place. And the remained H+ ion also made it acidic ame as OH- in the previous example made it basic.

Hydrogen takes copper's place.

H2 + CuSO4 = Cu + H2SO4

Blue colour of the copper sulfate solution will decrease as it is electrolysed. The gas bubbles are oxygen and hydrogen.

Copper metal in a powdered form will be discovered. the gas trapped in it is Hydrogen.

You electrolysed NaOH once. What would happen if you do with Na2SO4 sodium sulfate? It would not make anysense. It would be just piece water into hydrogen and oxygen. But we can have some fun with it. As a change of colour was happened in NaCl solution, the colour change of Na2SO4 will be more prominent. the colour of blue pea doesn't change with sodium sulfate because it is neutral. But when it is seperated in a regiform board, one side of it will be acidic and the other will be basic. As the - terminal ejects H2, there will be OH- left over where it is basic and + terminal will release O2 which keeps H+ in the solution to be acidic. OH- meets with Na+ and make a high basic concentration. While in the other side, H+ will meet (SO4) 2- to make sulfuric acid. but if we remove the regiform, both NaOH and H2SO4 will react each other to re make Na2SO4.

The solution is blue before the electrolysis happened.

The + side will be acidic and - side will be basic.

The main use of electrolysis is electroplating which is painting a metal on another metal type. This is done by connecting the metal which is to be plated in the negative terminal and the plated ingridient on the positive side. For this these should be a salt of the ingridient metal and also the metal should be less reactive than Hydrogen to stop reacting with acid and water. For an example, if you are plating iron with copper, you have to connect iron on the - terminal and a copper plate in the + terminal in a CuSO4 or CuCl copper chloride solution. If you are using Gold for the ingredient, you have to use a plate of gold in + side and a gold containing salt such as, AuSO4 gold sulfate. (Au is represented as Gold)

The thing happening is when the electrolysis happens, the copper gets out in the - terminal and attach to iron or the required metal. But the copper finishes after a time. But because of the copper plate in the + side, when the oxygen gas is released, copper react with it to form copper oxide. Then copper oxide react with made sulfuric acid to retain into copper sulfate and it cycles again. So that is why we have used carbon rods instead of a metal, or if we did, it might have reacted with O2 or Cl2 to make their corresponding oxides and chlorides.
 

CuO + H2SO4 = CuSO4 + H2O

Other uses of electrolysis are making of bases like NaOH, making of Cl2 gas, making of H2 and O2 gas, making of acids and sometimes making of metals such as Sodium.

 

Making of Sodium is done in the fused or molten media of salt which requires very high temperatures. Salts also get into ionizing in their molten media too. So once it is collected, it is extracted from the media. But don't try it at home.