Trick question? Shipwrecks and salvage (1 Viewer)

[thegink]

Personally, I said that the Mg would displace the Fe+ ions from solution (ie, the there is a buildup of iron ions (hehe) on the Magnesium.)

Then I thought that wasn't really worth 4 marks, so I said if one of them fell, and they touched, then there would be a path for the electrons, and so it would become a electrolytic cell. Which is pretty much the same, except the iron ions come out of solution onto the iron, and not the magnesium. I dunno if it's correct, and frankly, I don't care any more...

I guess we'll never know for sure??

 

[Abtari]

electrolytic cell = has a power source...

 

[missjelly_baby]

If you didn't know how to answer THIS question, you didn't study properly.

um was that aimed @ my "i don't know" comment cos i did study heaps for this exam. The only reason i wrote this was because it was my opinion and i didn't want to sound like someone who thinks they know everything and that they are absolutely correct. i've seen this too mauch in these exam forums - ppl who think they are sooo much smarter than everyone else. No offense to u personally touchstone but that is the reason.

 

[Oso]

I just made some stuff up. I said the water would react in favour to the solutes to produce H2 and O2. Now that I think about it though I'm pretty sure that only happens in an electrolytic cell. meh, nothing I can do about it now...

 

[Kyroth***]

I'm confused as to why this was so hard for everyone. I stopped working at the start of this year in protest to my horrid chem teacher (stupid, I know), but I didn't think anything of it. And from what's been written here, I'm pretty sure I got it right.

Oh, and for those who say it was 4 marks, so you had to write really good stuff, usually no. It'd be 1 mark for each of the equations, and 2 marks for the correct description. 4 marks, easy. Most questions, for most papers, are structured something like that.

 

[thestevonator]

You guys, it's a displacement reaction that occurs due to the presence of a more active metal(Mg) in the solution of a less active metal ion(Fe2+). Because magnesium is higher on the activity series than iron, it will preferentially oxidise and transfer its electrons to the Fe2+ ions- which is reduced. Therefore the Iron(II)sulfate fades in colour and a deposit of metallic iron forms on the magnesium. The concentration of Mg2+ ions hence increases in the solution. The iron nail in the solutions is unaffected as it has a lower reduction potential than Mg2+ ions. Does anyone happen to agree with me here?

 

[Captain Karl]

I think I agree, but its not the answer I put in the test.

 

[Touchstone]

um was that aimed @ my "i don't know" comment cos i did study heaps for this exam. The only reason i wrote this was because it was my opinion and i didn't want to sound like someone who thinks they know everything and that they are absolutely correct. i've seen this too mauch in these exam forums - ppl who think they are sooo much smarter than everyone else. No offense to u personally touchstone but that is the reason.

Nope, not directed at you. I personally thought that this was a free 4 marks, but then again people are good at different things. I think I stuffed the calculations for the calcium carbonate thing and some people may have found that a very basic question. No offence intended.

 

[Captain Karl]

Oh and Yumi Cheeseman, I think I know you! Do you go to Gosford High?

Who do you know from Gosford High? I go there

 

[taxman]

i don't know - i talked bout how it was like cathodic protection in that a more reactive metal (magnesium) will protect the less reactive (iron) against corrosion. therefore, magnesium was like sacrificial anode and it corroded where as iron did not. Like i said - i'm not sure but @ the tiem it seemed like the most correct thing to me.

I also went with this. Gave the oxidation, reduction and overall equations, explained that Magnesium would oxidise in preference forming Mg ions and that Iron ions would be reduced to form solid Fe.

I also agree with Kyroth that 4 marks for a question like this is practically a gift.

 

[thunderdax]

These kind of questions aren't free marks. Where did the iron form? Does the nail rust or not? They're both difficult questions to answer in this question and i bet most of you people who consider this as "free marks" got at least one of these wrong.

 

[brood22r]

What i think

In that trick question where there was the strip of mg and iron in the beaker with MgSo4 solution,

MgSo4 acts as the electrolyte just like NaCl as it is a salt.
Hence even though the solid Mg and iron is not drictly connected,
because of the electrolyte, they are indirectly connnected.

Hence the two metals will start corroding, but becuase Mg strip is
more reactive than the iron, Mg becomes the sacrificial anode and
iron becomes the cathode.

Hence Mg strip oxides and iron nail is protected from corrosion