shipwrecks, corrosion n conservation (1 Viewer)

[The_Crow]

The difference is in this the magnesium is ATTACHED to the iron hull. Read my above two posts for explanation.

Sacrificial anodes are attached to the hull because they don't have a propulsion method of their own. Clearly a ship can't just sail and have magnesium or zinc follow behind. Also, ships don't actually use magnesium as a sacrificial anode, it is only used in dry conditions because it is too reactive in water.

 

[Dumsum]

Sacrificial anodes are attached to the hull because they don't have a propulsion method of their own. Clearly a ship can't just sail and have magnesium or zinc follow behind. Also, ships don't actually use magnesium as a sacrificial anode, it is only used in dry conditions because it is too reactive in water.

Yes this I realise, it is zinc correct? It's not the point anyway. Electrons can't just zip through the water, instead they go straight to the iron ions. Thus no effect on the iron nail.

 

[The_Crow]

Of course electrons can't just zip through water, but the reaction isn't taking place in water, it's in an electrolyte. Directly from the dictionary, an electrolyte "is able to conduct electricity".

 

[Dumsum]

Of course electrons can't just zip through water, but the reaction isn't taking place in water, it's in an electrolyte. Directly from the dictionary, an electrolyte "is able to conduct electricity".

Difference being it's a movement of ions rather than a movement of electrons as in a conductor. In a galvanic cell, there needs to be both a movement of electrons from one electrode to the other and a movement of ions through the electrolyte.

 

[Abtari]

everybody,

I, personally, am not too happy with the way they asked this question. Clearly this is a sort of question that even someone not doing the option could answer - it is not something particular to Shipwrecks. In my opinion, it is directly related to the fourth focus idea in Production of Materials. It would have been better if they had asked something specific to what we have learned in this module.

Many people have showed different approaches to this question. This is a 4 mark question. I'm not sure what BOS will be looking for when marking, but whatever it is, I'm sure almost all of us (who wrote an answer for this, and thought they had done a satisfactory job of it) will fulfil some or most, if not all, of the criteria. If not 4, you are sure to get 3 or 2 at least. A mark or two is no big deal so don't take things to heart. And as long as you don't contradict yourself, then, you might even score the full 4 marks.

With regards to that 7 mark question, I thought that it was a bit essayish. However, if you had just focussed on the main concepts in chemistry, then you are sure (I think) to score near full marks. The way the question worded meant you just had to address their question. It's silly but had to be done I guess.

 

[~ ReNcH ~]

everybody,

I, personally, am not too happy with the way they asked this question. Clearly this is a sort of question that even someone not doing the option could answer - it is not something particular to Shipwrecks. In my opinion, it is directly related to the fourth focus idea in Production of Materials. It would have been better if they had asked something specific to what we have learned in this module.

Many people have showed different approaches to this question. This is a 4 mark question. I'm not sure what BOS will be looking for when marking, but whatever it is, I'm sure almost all of us (who wrote an answer for this, and thought they had done a satisfactory job of it) will fulfil some or most, if not all, of the criteria. If not 4, you are sure to get 3 or 2 at least. A mark or two is no big deal so don't take things to heart. And as long as you don't contradict yourself, then, you might even score the full 4 marks.

With regards to that 7 mark question, I thought that it was a bit essayish. However, if you had just focussed on the main concepts in chemistry, then you are sure (I think) to score near full marks. The way the question worded meant you just had to address their question. It's silly but had to be done I guess.

True. Actually Abtari, if you make an incorrect statement but you fulfil all of the criteria for the question do you know if you can still get full mark? (provided you don't contradict yourself by making that incorrect statement)

Btw. would there be any change of colour in the solution as more Mg ions are formed? I wasn't sure what the colour of each solution was, so I just stated that the colour of the solution may change

 

[Abtari]

True. Actually Abtari, if you make an incorrect statement but you fulfil all of the criteria for the question do you know if you can still get full mark? (provided you don't contradict yourself by making that incorrect statement)

Btw. would there be any change of colour in the solution as more Mg ions are formed? I wasn't sure what the colour of each solution was, so I just stated that the colour of the solution may change

well, i don't think there would be much of a colour change just by more Mg ions going into solution...so i didn't mention it. Maybe...well i'm sure unless they're BOS nazis, they won't cut any marks for writing that.

If you contradict yourself, you are likely to lose 1 mark. I think anyway.

 

[~ ReNcH ~]

well, i don't think there would be much of a colour change just by more Mg ions going into solution...so i didn't mention it. Maybe...well i'm sure unless they're BOS nazis, they won't cut any marks for writing that.

If you contradict yourself, you are likely to lose 1 mark. I think anyway.

Well, I don't think I contradicted myself....so hopefully I won't be penalised.

Btw. with the colour change...if the Mg strip and the Fe nail are large enough, then you'll get quite a significant transfer of ions out of solution...that was my reasoning, but then I wasn't sure if the solution had any colour in the first place

 

[Just James]

No! Unless i'm mistake the Iron nail would not rust... as if you put and iron nail in a solution of Iron does it rust.....? If you put an iron nail in a solution of magnesium it does not displace it either as magnesium is a stronger reductant.

Am i right?


Also... there is no deposit on the iron nail as it does not form a galvanic cell, there is no external wire connecting the two metals so how would electrons flow between?

The iron does not rust because it is within a solution containing a more active metal. Hence, the magnesium will corrode in preference to iron. As for the transfer of electrons, the presence of the electrolyte allows the electrons to travel from mg to fe.

We end up with a galvanic cell.

 

[jonemo]

The iron does not rust because it is within a solution containing a more active metal. Hence, the magnesium will corrode in preference to iron. As for the transfer of electrons, the presence of the electrolyte allows the electrons to travel from mg to fe.

We end up with a galvanic cell.

How in the world can that be a galvanic cell?
This is just simple displacement reactions going on in the cell- ie. magnesium displaces the iron ions in solution (iron forms on magnesium strip).

 

[Casmira]

i put acidic environment for hte first one, because more CO2 is dissolved in deep water

 

[Haku]

How in the world can that be a galvanic cell?
This is just simple displacement reactions going on in the cell- ie. magnesium displaces the iron ions in solution (iron forms on magnesium strip).

i agree. but it thought magnesium form non porous oxide layer.

 

[Captain Karl]

Just James is right, the iron doesnt rust because the magnesium is more reactive than it. The magnesium works like a sacrificial anode, making the nail a cathode. The electrons move through the electrolyte, as do the ions. The iron deposits on the nail and the magnesium corrodes until either all the magnesium or all the Fe 2+ ions are used up.

It works just like a galvanic cell, and if you connected a wire and a voltmeter to it you would get a reading (but not a maximum reading, since the electrons move through the electrolyte directly to the iron cathode). That is also why most galvanic cells are not created in the one beaker, to maximise current flowing through the wire.

 

[Abtari]

My answer agrees with Just James and Captain Karl.

 

[AreYouAlright?]

I agree with thunderdax i think he has hit the damn spot.

They gave us a solution Magnesium sulgate/iron(ii) sulfate solution allowing ions to be flowing or swapping or wateva

The same rules apply, magnesium will corrode, cuz its more reactive. The diagram is just the same thing Galvani set up, with two metals and a frog. Cuz the forg acted as the alectrolyte. and here the electrolyte is Magnesium Sulfate/iron (ii) sulafate solution

WRONG! Galvani's set up had the ends of two different metals tied together, the other ends were placed in freshly extracted frog leg muscle hence electrons could flow between them!

 

[Captain Karl]

My answer agrees with Just James and Captain Karl.

Good work.
Our teacher went through with us during the year stuff about how a galvanic cell can work work in one beaker, and an electrolytic cell can work in two beakers as long as the set-up is right.
So I'm 100% confident on this answer

 

[AreYouAlright?]

In regards to the chemistry course if you shoot yourself in the foot by making a contradiction you will not be awarded a mark because that shows you have not achieved the desired outcome as you are not sure.

In regards to this, if by the obscure chance it could be termed a galvanic cell which i strongly disagree to as there is no electron movement and an electrolyte refers to ion movement.

The Magnesium oxidises preferentially, the Iron(II) ions from the solution reduce to form Iron solid on the bottom of the beaker... after this process has completed there is Iron nail and Iron/magnesium solution. Iron in either Iron or magnesium solution will NOT undergo a displacement reaction as a) magnesium solution would be a stronger reductant b) Iron solution would be of the same activity.

I believe that you could say any of the following for marks:
-Magnesium oxidises
-Iron(II) ions from solution reduce to form Iron
-Magnesium is a stronger reductant and corrodes preferentially.
-Iron ions on solution reduce in concentration
-Magnesium Ions unaffected
-Metal displacement reactions occur!
-Iron does not corrode until Mg finishes at which point in time all other species are more active or of equal ability to oxidise therefore NO metallic displacement reaction occurs with Iron nail.

I would say that the word "galvanic" would be dangerous to use and you may lose marks.

Note: Electrolytes may allow flow of electrons but they would reduce the iron(II) solution NOT the nail!

 

[thunderdax]

In regards to the chemistry course if you shoot yourself in the foot by making a contradiction you will not be awarded a mark because that shows you have not achieved the desired outcome as you are not sure.

In regards to this, if by the obscure chance it could be termed a galvanic cell which i strongly disagree to as there is no electron movement and an electrolyte refers to ion movement.

The Magnesium oxidises preferentially, the Iron(II) ions from the solution reduce to form Iron solid on the bottom of the beaker... after this process has completed there is Iron nail and Iron/magnesium solution. Iron in either Iron or magnesium solution will NOT undergo a displacement reaction as a) magnesium solution would be a stronger reductant b) Iron solution would be of the same activity.

I believe that you could say any of the following for marks:
-Magnesium oxidises
-Iron(II) ions from solution reduce to form Iron
-Magnesium is a stronger reductant and corrodes preferentially.
-Iron ions on solution reduce in concentration
-Magnesium Ions unaffected
-Metal displacement reactions occur!
-Iron does not corrode until Mg finishes at which point in time all other species are more active or of equal ability to oxidise therefore NO metallic displacement reaction occurs with Iron nail.

I would say that the word "galvanic" would be dangerous to use and you may lose marks.

Note: Electrolytes may allow flow of electrons but they would reduce the iron(II) solution NOT the nail!

Er, You're wrong. Have you ever heard of the term cathode? Because according to what you're saying, the cathode is the bottom of the beaker. The fact is, the nail acts as the cathode and iron forms on it. I do agree with you about it definately not being a galvanic cell.

 

[Dumsum]

Er, You're wrong. Have you ever heard of the term cathode? Because according to what you're saying, the cathode is the bottom of the beaker. The fact is, the nail acts as the cathode and iron forms on it. I do agree with you about it definately not being a galvanic cell.

If it isn't a galvanic cell then there isn't a "cathode" or "anode" because there are no electrodes

 

[AreYouAlright?]

Er, You're wrong. Have you ever heard of the term cathode? Because according to what you're saying, the cathode is the bottom of the beaker. The fact is, the nail acts as the cathode and iron forms on it. I do agree with you about it definately not being a galvanic cell.

Agreed with Dumsum!..... As Iron(II) ions from solution are being reduced, it is impossible for it to form on the Iron nail as there is no way electrons can get to the other metal! No external circuit and they are not touching!!!

Besides, Magnesium strip is being eaten away, where does the Iron go then?.... the bottom of the beaker!