[Mrx2000]

So I'm doing an experiment on electroplating for the rust prevention of iron. I plated iron nails with copper, zinc and nickel and left them in water, salt water and water with sodium sulfite to also see the effect of salt and sodium sulfite. After a week it appears that the zinc has prevented rust (as expected) but the copper and nickel have not. I am now trying to measure the amount of rust that formed. I tried doing a titration of the salt water solutions left over by adding sulfuric acid and titrating with potassium permanganate but when I added the sulfuric acid, the teacher said the solution was supposed to turn clear but it remained the brown orange colour of the rust silt in the bottom (I poured off most of the water on top to get a concentrated solution). Then when I tried the titration, it was hard to see a change in colour because of the brown/orange colour already present. As such, I could not accurately find the concentration using the titration. So I tried using a conductivity meter but it was giving really weird results. Like the conductivity of a salt water solution we made up to compare to the solutions with rust showed a higher conductivity even though they had the samesalt concentration (and so the rust solution should have been higher because of the Fe(ii) in it right?). We used tap water so maybe some of the chemicals in it affected that but I don't know how. Maybe the conductivity meter was just broken. Either way, is there anything else I can do to measure how much rust was formed? Or is there something I did wrong in the titration or conductivity testing? Visually, it seemed I got the expected results but I'm having trouble getting any quantitative data... I will probably have to redo the tests now too which sucks. Anyways any help is appreciated!

[Borek]

It is not clear to me what you are trying to measure. Amount of iron that corroded? If so, you have to dissolve all the rust (HCl) and reduce it to Fe²⁺ before titration with permanganate.

Using conductivity when you are working with poorly defined mixtures is asking for troubles.

In every analytical procedure DI water is a must.

[Mrx2000]

It is not clear to me what you are trying to measure. Amount of iron that corroded? If so, you have to dissolve all the rust (HCl) and reduce it to Fe²⁺ before titration with permanganate.

Using conductivity when you are working with poorly defined mixtures is asking for troubles.

In every analytical procedure DI water is a must.

Yep so amount of iron corroded is what I am trying to measure. I tried to dissolve the rust with sulfuric acid (however the brown precipitate at the bottom did not dissolve). Do you know of a good way to reduce it to Fe(II) because it seems that is the only step I might have been missing. And also, yes I think for this retest I will definitely use DI water. I am just worried that somehow the salt in the water (NaCl) is disrupting the titration or more likely the ability for the iron to be dissolved in the water. From what I understand the silt at the bottom is Iron Hydroxide and maybe some of this is being oxidised by the water. Is this what needs to be reduced back to Iron (II)? If so what is the reaction for the reduction of the Fe(III) with water and how can I reduce that product back to Fe(II)?

[Borek]

I tried to dissolve the rust with sulfuric acid (however the brown precipitate at the bottom did not dissolve).

Hydrochloric is much better. If it doesn't dissolve, chances are it is not just rust. At least in the sample with copper it can be the layer of copper that fell off.

Do you know of a good way to reduce it to Fe(II) because it seems that is the only step I might have been missing.

As you have a lot of Fe³⁺, column with granulated zinc (so called https://en.wikipedia.org/wiki/Jones_reductor ) would be probably best.

More on the permanganate titration: http://www.titrations.info/permanganate-titration-iron

Alternatively you can try to dissolve the rust, make sure it is oxidized to Fe³⁺ and look for a way of determining amount of Fe³⁺. Depends on what kinds of glass/reactants you have available.

I am just worried that somehow the salt in the water (NaCl) is disrupting the titration or more likely the ability for the iron to be dissolved in the water.

Hope, shouldn't. Actually presence of chlorides is a bit beneficial, they will complex the iron, which is why hydrochloric acid is better than sulfuric.

From what I understand the silt at the bottom is Iron Hydroxide and maybe some of this is being oxidised by the water.

Which Iron hydroxide? Fe(II) or Fe(III)? Can Fe(II) survive in the presence of air oxygen?

Is this what needs to be reduced back to Iron (II)?

See above.

If so what is the reaction for the reduction of the Fe(III) with water and how can I reduce that product back to Fe(II)?

No such thing as reduction of Fe(III) with water, TBH I have no idea what you mean.

[Arkcon]

I tried to dissolve the rust with sulfuric acid (however the brown precipitate at the bottom did not dissolve).

Hydrochloric is much better. If it doesn't dissolve, chances are it is not just rust. At least in the sample with copper it can be the layer of copper that fell off.

Mrx2000:, you have to review your procedures more carefully.  Your text blocks are kinda all over the place.  As an example, write an outline: each metal zinc, iron, copper, etc, and each possible acid: sulfuric, hydrochloric and other.  What acid dissolves what metals and what oxides, what ends up in solution and what do you measure?

If you dissolve the iron and the rust in sulfuric, what are you measuring?