How Does Ion Charge Affect Mass Deposition in Electrolysis?

[AdamCFC]

Just an extra thing to my last post. I would like to include a hypothesis, does this sound suitable and where would i put it?

If moles deposited is related to ion charge, then increasing the charge will increase the current and mass change, which in turn will increase the amount of metal deposited.

Do the bits in bold need to be re-arranged?

 

[Bystander]

You have written "I" as the product of four terms. If you hold three constant and change 1, "I" is linear in that one term. If you hold two constant, and change the product of two others, "I" is linear in the product of those two terms. If you hold one constant, change the product of two others, and have no control over the third, you're in trouble.

"Mass" or "moles?" Both start with "m," but they are NOT interchangeable.

You can discuss crumple zones --- you can count charge carriers, the product of charge carrier concentration and charge --- you can distinguish between mass and mole.

 

[AdamCFC]

Was what i said about crumple zones right, id feel terrible if i was giving someone false information.

Okay, i think that's fine now :) My intention was to control n A and v and just change e. That would have given me a linear trend. Due to errors and things i couldn't control precisely (temperature), i only controlled ...

wait, i havnt controlled/kept constant anything?

n - didnt 100% understand what you said about ion concentration per unit volume, but i understand that by using 100ml at each at 0.1mol, that was not enough to control ion concentration, and i did not control this well.

A - The surface area varied with each run

This is what is termed "throw," and is different for every metal and for every plating solution/recipe. Some metals cover the cathode more uniformly than others. You can get smooth plating films, rough blobs and gobs, metals that grow staghorns and trees. It's part of the "art" that is necessary to make a living running a plating shop.

v - Volts - Kept constant
-- Temperature - Did vary day by day, not much, but there was a change

This is not a total diaster ... as far as schoolwork goes, because.
I have a trend that supports my prediction and hypothesis
I have a lot of errors i can talk about, and most importantly, describe how to minimise/eradicate in future experiments. e.g, do all tests at a controlled temperature.

 

[Bystander]

Was what i said about crumple zones right, id feel terrible if i was giving someone false information.

Wasn't wrong. You gave a hint, pointed to a source --- abided by the "don't do their work for them, get them to do it themselves" spirit of the homework forum.

I was pointing out to you that you are NOT a babe in the woods --- that stuff's been covered for you and basic concepts relevant to this electrolysis problem haven't been. Punched the frustration button there for me.

Okay, i think that's fine now :) My intention was to control n A and v and just change e. That would have given me a linear trend. Due to errors and things i couldn't control precisely (temperature), i only controlled ...

wait, i havnt controlled/kept constant anything?

n - didnt 100% understand what you said about ion concentration per unit volume, but i understand that by using 100ml at each at 0.1mol, that was not enough to control ion concentration, and i did not control this well.

A - The surface area varied with each run

v - Volts - Kept constant
-- Temperature - Did vary day by day, not much, but there was a change

This is not a total diaster ... as far as schoolwork goes, because.
I have a trend that supports my prediction and hypothesis
I have a lot of errors i can talk about, and most importantly, describe how to minimise/eradicate in future experiments. e.g, do all tests at a controlled temperature.

So long as you learn, there are NO "total disasters." Good.

You predict a "linear trend." Let's work on that, because there is something in "I=nAve" that is still leading you off into the weeds.

Looking just at silver and iron, +1 and +3 charges, you expect to see the current triple; you are going to "measure" current by weighing the cathode of each cell before and after a timed electrolysis and calculating moles plated onto the cathode. What is your prediction for the number of moles of iron? Less than, greater than, or equal to the number of moles of silver?

 

[AdamCFC]

er, I am not sure. I don't think i expect iron+3 to have three times more moles deposited than silver +1. I do expect a proportional relationship though. I expect more moles deposited on the cathode after using the iron electrolyte than the silver electrolyte. This is because iron ions have a higher charge.

Am i right in thinking, because silver has almost double the atomic mass of iron, that 10 iron ions would need to be plated to equal 5 silver ions?
If this is the case, because iron deposited a higher mass change than silver, many many more ions were deposited on the cathode than the amount of silver ions deposited.

Going on holiday wednesday morning, so won't be able to reply after that until the 1st sept.

Adam

 

[Bystander]

er, I am not sure. I don't think i expect iron+3 to have three times more moles deposited than silver +1. I do expect a proportional relationship though. I expect more moles deposited on the cathode after using the iron electrolyte than the silver electrolyte. This is because iron ions have a higher charge.

Wrong. You have increased the current by increasing the charge on the ion. You have not increased the number of ions being deposited. Silver at +1 carries a current I; iron at +3 carries a current of 3I. A silver ion will be reduced by ONE electron to atomic (metallic) silver at the cathode; a ferric ion requires THREE electrons to be reduced to metallic iron. Recheck the definition of electric current.

Am i right in thinking, because silver has almost double the atomic mass of iron, that 10 iron ions would need to be plated to equal 5 silver ions?

You are determining mass only as a means to find the numbers of moles deposited; other than for that purpose, mass is meaningless in the context of this experiment.

If this is the case, because iron deposited a higher mass change than silver, many many more ions were deposited on the cathode than the amount of silver ions deposited.

Yes. But, please think in terms of moles rather than mass. You want to count charge, you want to count moles, you want to compare those numbers rather than masses.

Going on holiday wednesday morning, so won't be able to reply after that until the 1st sept.

Adam

 

[AdamCFC]

Ok, so to your previous question, I predict there will be more moles of iron deposited than moles of silver.

there is something in "I=nAve" that is still leading you off into the weeds.

Whats that?

 

[Bystander]

Silver ion at +1, current is I; ferric ion at +3, current is 3I. WHAT is the definition of current? Same time for both cells, total charge transferred is what for silver? And what for iron? Reducing how many moles of silver? And how many moles of iron?

You've got two guesses left.

 

[AdamCFC]

Current represents the flow of electrons through a conductive material.

Silver needs 1 electron to become an atom again, Iron needs 3.

 

[Bystander]

Current is defined as CHARGE per unit time, be that charge carried by electrons, or ionized atoms or molecules.

Now, more moles of iron than silver? Same? Fewer?

 

[AdamCFC]

More moles of iron than silver.
More mass deposited using iron than silver.
Higher current using iron than silver.

 

[Bystander]

Wrong.
Wrong.
Right.

Charge is defined as the sum of the products of the numbers of charge carrying species with the numerical values of the charges on the species.

Try again.

 

[AdamCFC]

sorry this is over my head, its just guesses now. looking at my results, iron deposited more moles than silver and copper.

 

[Bystander]

We're working on your prediction which you are then going to compare to the results.

If cations are the only charge carrying species in solution, silver at +1, or iron at +3, at the same concentration, you predict three times the current. If you weigh the cathodes, divide by atomic weight to get number of moles, and compare the number of moles, is the number of moles of iron less than, equal to, or greater than the number of moles of silver?

 

[AdamCFC]

Silver - 0.033g / 108 = 0.000306moles

Iron - 0.110g / 56 = 0.001964moles

The number of moles of iron(1964) is greater than the number of moles for silver(306).

 

[Bystander]

I'm not even going to ask where those numbers came from.

One silver ion is reduced in time t; one ferric ion is reduced in the same time t. For silver, the current is one unit charge over t; for iron the current is 3 unit charges in the same time t, or three times greater current. The number of moles of silver is one over Avogadro's number; the number of moles of iron is ONE over Avogadro's number.

 

[AdamCFC]

those were the exact numbers out of my coursework table, look at the moles deposited table.