# Electrolysis, charge of ions.

Hi, my names Adam, this is my first post I am in year 10 UK (10th grade i believe)

This is not a homework question, its advice towards the analysis of my chemistry coursework.
Im predicted an A* in chemistry so this is why my experiment is more complicated than others in my class.I based my experiment on electrolysis, I changed the charge of the ions, referring to the formula I=nAve, by increasing charge of ions (e), current (I) will increase, which is directly proportional to moles deposited. I weighed the cathode before and after using my 3 electrolytes, which had a charge of +1,+2 and +3. I noticed the trend i would expect, higher charge = higher mass deposited thus higher moles deposited. This may sound stupid, but why is the weight higher, do higher charge ions have a higher mass? are more attracted to the cathode? can you explain the weight difference.

"Not homework?" Schoolwork is "homework." This needs to be moved.

That said, you have omitted ALL the information pertaining to the actual conduct of the experiment. You've given us a statement of the object of the experiment, and of your conclusion, but nothing about experimental details. Fill in the blanks and we'll give you a few hints through the trickier conceptual parts (which you've completely misunderstood to this point).

ok, sorry, shall i run through my method?

Yes. You might want to read the homework guidelines --- it'll save a lot of time.

ok, i badly feel as if i have got off to the wrong start

Our objective was to see how changing the four major factors in the formula I=nAve affects the overall current (Amps). My group of three was made up of the smarter people in the class, so instead of changing A (surface area of electrodes) or v (velocity - temperature or voltage) we changed e (charge of ion).

Because I is directionally proportional to moles deposited we will weigh the cathode ( because we are changing the postive ions) before and after we electolyse the electrolyte. By finding the mass change we can then divide it by the atomic mass of the element and find the moles deposted.

We used three electrolytes :
Silver Nitrate AgNO3 +1 ion charge
Copper Chloride CuCl +2 ion charge
Iron Chloride FeCl + 3 ion charge

As i expected, we saw the trend we expected, the higher the charge of ion, the bigger mass change, more moles deposited.

Because the higher charge ions have a higher charge, are they attracted to the cathode more vigerosly, do they have a higher mass. Essentially, can you help explain why the higher charged electrolytes deposited more metal on the cathode. This may be a stupid question.

Much better, thank you.

Now, we still need to know some things: currents you observed for each cell; times you left the cells running between weighings of the cathodes; cathode materials; anode materials --- and, if just the list of missing information is hint enough for you, drop in again sometime.

ok, i first used copper electrodes, but after my preliminary tests, i found in the CuCl solution, copper was transfering off the anode into the electrolyte, then onto the cathode, this makes the test unfair, so i changed to graphite electrodes which are very unreactive.

I electrolysed the solutions for 2minutes at 12V each time.

Do you need the info on the currents? as i have already found out the moles deposited from the mass change. But i would like to know more about the characteristics of +1,+2, and +3 charged ions.

(snip) ... , by increasing charge of ions (e), current (I) will increase, which is directly proportional to moles deposited. I weighed the cathode before and after using my 3 electrolytes, which had a charge of +1,+2 and +3. (snip)

(snip)Our objective was to see how changing the four major factors in the formula I=nAve affects the overall current (Amps). (snip)Because I is directionally proportional to moles deposited we will weigh the cathode ( because we are changing the postive ions) before and after we electolyse the electrolyte. By finding the mass change we can then divide it by the atomic mass of the element and find the moles deposted.
We used three electrolytes :
Silver Nitrate AgNO3 +1 ion charge
Copper Chloride CuCl +2 ion charge
Iron Chloride FeCl + 3 ion charge

As i expected, we saw the trend we expected, the higher the charge of ion, the bigger mass change, more moles deposited.

Because the higher charge ions have a higher charge, are they attracted to the cathode more vigerosly, do they have a higher mass. Essentially, can you help explain why the higher charged electrolytes deposited more metal on the cathode. This may be a stupid question.

ok, i first used copper electrodes, but after my preliminary tests, i found in the CuCl solution, copper was transfering off the anode into the electrolyte, then onto the cathode, this makes the test unfair, so i changed to graphite electrodes which are very unreactive.

I electrolysed the solutions for 2minutes at 12V each time.

Do you need the info on the currents? as i have already found out the moles deposited from the mass change. But i would like to know more about the characteristics of +1,+2, and +3 charged ions.

Currents AND mass changes.

okay, this is going to get really complicated now.

I tested each electrolyte 3 times to find an average, i eliminated any outliers.

Element # Test No. # Mass Change # Atomic Mass # Moles Deposited

Ag+1-------I]1) 0.082 /108 = 0.000759 ***OUTLIER***[/I]
--------------2) 0.033 /108 = 0.000305
--------------3) 0.032 /108 = 0.000296
AVERAGE MOLES DEPOSITED FOR +1 = 0.0003008

Cu+2--------1) 0.070 /63.5 = 0.00110 ***OUTLIER***
--------------2) 0.040 /63.5 = 0.00063
--------------3) 0.030 /63.5 = 0.00047
AVERAGE MOLES DEPOSITED FOR +2 = 0.00055

Fe+3----------1) 0.110 /56 = 0.00196
---------------2) 0.110 /56 = 0.00196
---------------3) 0.106 /56 = 0.00189
AVERAGE MOLES DEPOSITED FOR +3 = 0.00194
Sorr its hard to read, this format won't let me set it out clearly

Now if i simplify my averages, i get 30, 55, and 190. This shows the trend i would have expected, although i believe this is wrong. The ion charge went up by 1 each time (+1,+2,+3) so i would expect the averahes to be more linear, say 50, 100 and 150. Agian, hers the complicated bit, on Cu+2, we see i have taken Test No.1 as the outlier, well suppose that is the correct value, and Test No 2 and 3 are actually outliers, then my averages would look like this. 30, 110, 190 ---- this is almost a perfectly linear incline, going up by 80 each time.
Does this make sense?

CURRENTS! Those numbers from that "thing" called an ammeter; they're what the experiment is all about.

The mass changes are what? Grams, tons, kilograms?

You used the same electrodes throughout the experiment?

I didnt put the currents in because they don't seem to be included in my results. That "thing" called an ammeter was connected to a variable resistor in my circuit.
The initial amp reading at the start of each test was 0.65 amps.
Silver+1 1)0.71 2)2.62 3)2.92
Copper+2 1)0.75 2)0.81 3)0.78
I don't have the results for Iron+3.

Sorry about the mass, yes they are grams. After preliminary findings, i changed to graphite electrodes, yes i used them for all tests to keep it fair.

Input volts i have already said ...

I electrolysed the solutions for 2minutes at 12V each time.

You seem to have ignored my moles results, do you agree? do you understand my theory about
the wrong outliers, and that it should be linear?

and i just need to know about the charged ions; my original question.

Last edited:
Enough with the "20 Questions" --- you're probably trying to get this finished up to turn in Monday. You've been cooperative, so we'll get to the bottom line --- your experiment is a disaster both in design and data, and none of that is your fault; you haven't picked up too well on hints steering you in more productive directions with your analysis, and that could be my fault, yours, your school's, or some combination.

Graphite anodes? Probably not a problem. Graphite cathodes? Kiss of death for weighing purposes, kiss of death for "constant area." Constant voltage? Pointless --- a perfect electrolysis setup is going to present a zero voltage drop. Compare your electrolytes at constant current to see the effect of ionic charge.

"Relationship between mass and charge?" No silver platter for you on this one: 1) recall the definition of an ion; 2) compare the mass of that ion to that of the neutral parent atom; 3) plate that ion out on your cathode and think about what is involved in the interactions of ions, electrons, and neutral atoms in the plating process.

Recall the definition of electric current; compare that to the mass required per unit time to carry an equivalent amount of charge for mono-, di-, and tri-valent cations.

I'll duck in every hour or so for questions --- you got handed something totally inappropriate to any reasonable expectations for your level in the educational process, and it has confused you far more than enlightened you.

First let me thank you for your time and help

My design is ok, and my data could be better let's say, but it does show a trend. In england were currently on summer holidays, so this isn't due for at least another 6 weeks.

I don't understand what your saying about the electrodes, i can assure you the weighing was fair and we kept everything constant. The depth the electrodes were in the solution was measured, and the distance apart was kept constant.

I wanted to know more about ions, i already understand a bit, and a bi about ionic bonding. (not trying to sound big headed) but I am top of my GCSE class, but a lot of what your saying is going over me. We havnt learned about mono, di or trivalent cations, could you explain easily? if not, then its not a problem. I wanted to know how to justify the different mass changes, is because +3 ions are attracted to the cathode more vigerously then the +1 ions. Or is it because +3 ions already have a bigger mass than +1 ions. Sorry if I am sounding stupid here, but I am trying.

I have attached a copy of my coursework so far, its not much and I am sure its not perfect, but maybe it can explain my experimant better. I have a lot of results, explanation, analysis and conclusion material in note form in my book which i have yet to write up. I will knuckle down over the next few days to get a better version for you to see, if you still care.

Once again, thanks for your help :) please take a look at the attachment.

#### Attachments

• 2010 GCSE Chemistry Coursework electrolysis.pdf
451.4 KB · Views: 1,096
Six weeks --- that's plenty of time to work this out for you. Haven't been able to open the attachment yet --- takes a little time for it to clear hurdles set up to reduce spam. Once it's clear, I'll look that over and get back to you.

I can view it, and there's 3 views? is it visible to you yet?

"There was an error opening this file." Eleven views. Can you give me a short summary with "spoilers," and we'll get on with this?

Opened fine for me. Here are the important parts:

Thankee, Gokul // Give me a couple hours with this, AdamCFC, and I'll get back to you with a couple more questions/hints.

EDIT: sorry for some reason Gokuls post didnt come up at first, cheers for that :) Like i say, that's all i have written up, i have a results table, a graph, although that's on paper but i could re-create on word, and some analysis, ill upload more during the weekend :)

Last edited:
"By increasing any of the above, overall, ... ;" and, you are controlling n, A, v constant to test your hypothesis.

The way PF is supposed to work is that you ask for help, and people give you hints rather than doing the work for you --- my preference is to ask you questions that lead you to the answer to your question. I ain't messing with you --- I want you to understand the principles behind the things you're trying to learn.

"A" we won't worry about for now, you've taken appropriate steps to keep that constant; there are refinements we can discuss later.

Now for the first couple questions: 1) do you understand the distinction between voltage and velocity for "v?" 2) how are you keeping "n" constant for your three solutions? State the concentrations you used for each, and remember the definition you've given for "n."

Here goes; Velocity is the speed and direction the ions have, does this relate to kinetic energy of the ions? By increasing the voltage or temperature you can give the ions more energy, through either thermal energy or kinetic energy and this can increase the velocity. So to keep the "v" constant, i must keep the voltage and temperature the same. I can keep the voltage the same through the power-pack, and eliminate errors by using the same power-pack throughout my experiment, as its very hard to keep the temperature the same in a classroom enviroment, i have/will state that I am doing all 3 tests during a 3 day period, at room temperature. This is as accurate as i can make it.

I am keeping "n" constant by using the same amount of electrolyte at the same molarity? I used 0.1mol concentrations for each electrolyte. "n" is number of ions.

Is this right though :(, i am assuming all three solutions have the same proportion of ions? <--- does that make sense?

Here goes; Velocity is the speed and direction the ions have, does this relate to kinetic energy of the ions? By increasing the voltage or temperature you can give the ions more energy, through either thermal energy or kinetic energy and this can increase the velocity. So to keep the "v" constant, i must keep the voltage and temperature the same.

"Yes --- and --- no." The expression you've been given to work with, "I=nAve," is missing a couple details: 1) n is the number of ions per unit volume (concentration); 2) it is necessary to sum over ALL ion species. The actual "drift" velocity of ions in aqueous solution at room temperature is so low as to be insignificant compared to the velocities due to random thermal motion (fingers crossed, you've been introduced to Brownian motion, or Boltzman, or some discussion of molecular/atomic vibration at temperatures above absolute zero. If not, holler.

I can keep the voltage the same through the power-pack, and eliminate errors by using the same power-pack throughout my experiment, as its very hard to keep the temperature the same in a classroom enviroment, i have/will state that I am doing all 3 tests during a 3 day period, at room temperature. This is as accurate as i can make it.

You're aware that you have to control these factors, and did what you could with the resources available. Cool.

I am keeping "n" constant by using the same amount of electrolyte at the same molarity? I used 0.1mol concentrations for each electrolyte. "n" is number of ions.

Is this right though :(, i am assuming all three solutions have the same proportion of ions? <--- does that make sense?

Okay, much as I suspected. I drop silver nitrate, AgNO3, into water and it dissolves to give me a silver cation, Ag+,and a nitrate anion, NO3- in solution, TWO charge (current) carrying species.

Given that information, what happens when I drop cupric chloride, CuCl2[/ (one copper atom combined with two chlorine atoms), into water?

And, it's your bedtime --- catch you in the morning.

No,we havnt been introduced to any of those laws :(, i think that's more A level stuff, do you have the same grade system in america, GCSE, A Level?

Would Copper Chloride issolve into Cu+ anion, and 2Cl- cations.
Would Iron Chloride dissolve into Fe+ anion and Cl- cation.

Finally, because the Anode is positive, because the metals become postively charged, don't they become an-ions, instead of cations?

No,we havnt been introduced to any of those laws :(, i think that's more A level stuff, do you have the same grade system in america, GCSE, A Level?

The energy a charged particle (anion or cation) would acquire "falling" freely through an electrical potential difference is just the potential difference in volts times the charge number times 100kJ/mol; this is forty times greater than the thermal energy of particles of equivalent mass at room T. However, when "freefall" is obstructed as in ions in aqueous solution, tens to hundreds of collisions with neutral particles occur for every nanometer of travel in the potential gradient, robbing the ion of the energy it would have picked up in freefall.

The educational fads in the U.S.? Gibberish, political correctness, sensitivity, and who knows what other nonsense translated into seat time equals diplomas for nincompoops, and actual learning and demonstrated skills are penalized --- guess that'd be "Lysenko's New Soviet Man."
Would Copper Chloride issolve into Cu+2 [STRIKE]anion[/STRIKE]cation, and 2Cl- [STRIKE]cations[/STRIKE]anions.
Would Iron Chloride dissolve into Fe+3 [STRIKE]anion[/STRIKE] cationand three Cl- [STRIKE]cation[/STRIKE]anions.

"Conservation of charge," one of seven conservation laws chiselled literally in stone; ions produced from a neutral substance HAVE TO OBEY.

One mole of silver salt equals two charge carrying species, one mole of copper? And iron?
Finally, because the Anode is positive, because the metals become postively charged, don't they become an-ions, instead of cations?

Cation, a positively charged species formed when a neutral species gives up an electron; Cathode, an electrode that gives electrons to other species, or vacuum (in a CRT), and "cat-" can be regarded as a prefix meaning "source of electrons."

Anode, an electrode that "sinks" electrons from an electrical circuit or from species in solution; Anion, formed when a neutral species accepts, takes, picks up, acquires an electron from some electron source.

"Cathode" and "anode" can be a little tricky to interpret on occasion --- stick with the definitions, and you'll usually be okay.

Ok, so:
-Anode is the positive electrode
-Cathode is the negative electrode
-An-ions are attracted to the An-ode because they are negatively charged
-Ca-tions are attracted to the Ca-thode because they are positively charged

Also, do i need to include information about the ion masses? if so, would Cu+2 be, the mass of a copper atom, minus the mass of 2 electrons?

I will upload a improved version soon, if you can't view it, shall i email it to you, because I am not sure to show it how gokul did.

Ok, so:
-Anode is the positive electrode
-Cathode is the negative electrode
-An-ions are attracted to the An-ode because they are negatively charged
-Ca-tions are attracted to the Ca-thode because they are positively charged

Works.
Also, do i need to include information about the ion masses? if so, would Cu+2 be, the mass of a copper atom, minus the mass of 2 electrons?

No. When the cation reaches the cathode, it picks up electrons (is reduced).
I will upload a improved version soon, if you can't view it, shall i email it to you, because I am not sure to show it how gokul did.

Don't worry too much about revision just yet --- fair amount of ground still to cover. You do see that "n," the number of charge carrying species is not conserved among your three different salts? You do understand that both cations and anions contribute to current flow?

Last question for the day: what happens to the concentration of cations you started with in solution when cations are reduced at the cathode?

The concentration reduces, because the cations are reduced; they give up their excess electrons to the cathode, and turn into atoms which get plated/stuck to the cathode. The anions gain electrons from the anode and are released into Chlorine gas, or Nitrous Oxide?(in my cases).

Yes i know that both ions contribute to current flow, but I've never fully understood why, let's say the flow of electrons is anticlockwise,(conventional current and the real way confuse me). So the electrons flow from + on the battery to the anode, then "stop", electrons are then given to the cathode by cations, and those electrons continue to the - on the battery and carry on basicly completing the circuit even know there is no "loop" as such... i don't see the relevence to current flow with the anions, because their electrons are traveling the "wrong" way, because they gain the electrons they need from the anode, and basically do nothing after? As far as i can tell, they don't actually help the flow of electrons in the circuit.

The concentration reduces, because the cations are reduced; they [STRIKE]give up their excess electrons to the cathode[/STRIKE] pick up electrons from the cathode (the cathode is an electron source; they gave up electrons to become cations --- picking up electrons turns them back to neutral atoms), and turn into atoms which get plated/stuck to the cathode. The anions [STRIKE]gain[/STRIKE] donate electrons [STRIKE]from[/STRIKE] to the anode and are released into Chlorine gas, or Nitrous Oxide?(in my cases).

Depends on solvent, electrode material, voltage, current density, and a whole lot of other variables; a not uncommon result is that the solvent is reduced, forming oxygen and hydrogen ions (acidifying the solution with hydrochloric or nitric acid for your two anion choices).
Yes i know that both ions contribute to current flow, but I've never fully understood why, let's say the flow of electrons is anticlockwise,(conventional current and the real way confuse me). So the electrons flow from + on the battery to the anode, then "stop", electrons are then given to the cathode by cations, and those electrons continue to the - on the battery and carry on basicly completing the circuit even know there is no "loop" as such... i don't see the relevence to current flow with the anions, because their electrons are traveling the "wrong" way, because they gain the electrons they need from the anode, and basically do nothing after? As far as i can tell, they don't actually help the flow of electrons in the circuit.

"Anode-cathode confusion." Let's try a different approach.

The battery (single cell) has a positive and negative terminal. When used as a source of electrical current in a circuit, the positive terminal functions as the anode within the circuit; the negative terminal as the cathode. When you are looking at the chemistry within the cell itself, the electron flow from the circuit is TO to positive terminal of the battery, and from there INTO the electrolyte within the cell, electron source = cathode.

If you are outside the cell, the positive battery terminal is the anode; if you are inside the cell, the positive battery terminal is the cathode.

I got really confused on my last post, which is annoying as I am starting to look like an idiot. Heres what i meant to say:

I now know electrons travel from the - terminal to the + terminal, electricty travels from negative to positive.

The concentration of cations reduces, because the cations are reduced. They are attracted to the cathode where they "take "electrons to become neutrally charged atoms which get plated/stuck to the cathode. The anions are attracted to the anode because they have more electrons than protons so have a overall negative net charge, the anions "deposit" electrons onto the anode, then becoming neutrally charged atoms and are released into Chlorine gas, or Nitrous Oxide.(in the silver nitrate case, are the gasses released Nitrogen + Oxygen, or Nitrous Oxide?).

Is it right to say, the concentration of ions decrease as time goes on? Is that why the current reading should decrease, even know i didnt measure that?

This brings me on to how both ions affect current flow. I don't understand why. I am imagining a loop, the electrons travel from - to +, anticlockwise. I imagine the loop is broken, i don't really see how relevant the cations are, they are not helping electrons get to the + on the battery, on the other hand, the anions are "giving" electrons to the anode, which allows a flow to continue to the + on the battery, is my idea making sense?

I think I am getting off track here, i have updated my coursework now, it has my graph I've scanned onto, which i think you will find interesting, my mass change results, my moles results, and some analysis. Shall i attach it to my next post?

If there's some trouble opening your PDFs, you could try attaching image files instead. Also, the way I displayed images in-thread was by uploading them to an image hosting site (like tinypic.com) then copying the URL for the image file from there and putting it in between [noparse] [Broken][/noparse] tags.

Last edited by a moderator:
I got really confused on my last post, which is annoying as I am starting to look like an idiot.

You're starting to look like someone trying to learn something.

Heres what i meant to say:

I now know electrons travel from the - terminal to the + terminal, electricty travels from negative to positive.

The concentration of cations reduces, because the cations are reduced. They are attracted to the cathode where they "take "electrons to become neutrally charged atoms which get plated/stuck to the cathode. The anions are attracted to the anode because they have more electrons than protons so have a overall negative net charge, the anions "deposit" electrons onto the anode, then becoming neutrally charged atoms and are released into Chlorine gas, or Nitrous Oxide.(in the silver nitrate case, are the gasses released Nitrogen + Oxygen, or Nitrous Oxide?).

Is it right to say, the concentration of ions decrease as time goes on? Is that why the current reading should decrease, even know i didnt measure that?

Close enough for starters.
This brings me on to how both ions affect current flow. I don't understand why. I am imagining a loop, the electrons travel from - to +, anticlockwise. I imagine the loop is broken, i don't really see how relevant the cations are, they are not helping electrons get to the + on the battery, on the other hand, the anions are "giving" electrons to the anode, which allows a flow to continue to the + on the battery, is my idea making sense?

See? You're learning --- you're asking questions that I have to stop and think through very carefully.

Current flow through wiring, ordinary alectrical circuits --- charge carriers are electrons; get to doped junctions in semiconductors, we've got electrons and holes --- and, no, I've not got my own mind wrapped around the hole concept well enough to even try explaining it to someone else.

Electrolytic cells come in quite a few flavors to accomplish quite a few different purposes: 1) electrolytic refining (of Cu, for instance) is accomplished by dropping a copper anode and a copper cathode into a sulfuric acid or copper sulfate solution, the Cu in the anode giving up electrons to the circuit driving the cell, that circuit carrying electrons to the cathode while copper ions from the anode move through solution to the cathode where they combine/recombine yielding electrolytically refined copper (current through the cell is exclusively cationic); 2) electrolysis cells (of water for instance) break down compounds by reduction of an oxidized species at the cathode and oxidation at the anode, and current through the electrolyte is carried (hopefully in a well designed cell) by a stoichiometric ratio of the cations and anions being reduced and oxidized; 3) batteries (disposable) by a variety of chemistries both public domain and proprietary that I'm not comfortable enough with to go into a whole lot of detail; 4) rechargeable batteries and I can't remember how lead-acid batteries operate right now, let alone nicads, lithium ion, and whatever else has come out.

Now, I'm looking like the idiot --- I'm trying to coach you, and have just admitted how little I know

Electrode selection, electrolyte selection, solvent, voltage, and current determine the chemistries taking place at electrodes as far as oxidations and reductions go; these also determine how current is partitioned between charge carriers (cations and anions). Good place to give you an example of the anion charge carrier mechanism --- we'll say you're doing electrolysis of water with KOH (potassium hydroxide) as your electrolyte. Hydroxide ions, OH- are attracted to the anode, give up an electron to the anode forming hydroxide radicals, OH., and two radicals combine to form hydrogen peroxide which decomposes to water and oxygen. Where's the hydroxide come from to replace what I just destroyed at the anode? K+ is attracted to the cathode, and since it's hydrated (surrounded by water molecules attracted by charge-dipole interaction), the electron it picks up from the cathode reduces water rather than the potassium ion, forming a hydrogen radical, H. and a hydroxide ion.

That's probably enough to chew on and digest for the moment.
I think I am getting off track here, i have updated my coursework now, it has my graph I've scanned onto, which i think you will find interesting, my mass change results, my moles results, and some analysis. Shall i attach it to my next post?

Yeah, let's see what are you got.

Heres the Improved coursework, its still missing a detailed analysis, evaluation and conclusion.
You should be able to view straight away, if not i can email it to you, or upload the pictures like gokul did :)

#### Attachments

• 2010 GCSE Chemistry Coursework electrolysis.pdf
1.3 MB · Views: 531
"This file cannot be found."

Have you got any more information on currents? At thirty seconds, minute, end of run?