shipwrecks (1 Viewer)

[xeriphic]

could anyone tell me at what depths does aerobic organisms begin to occur, also how can carbon dioxides concentration in seawater greater than atmosphere if the presence of phytoplankton photosynthsise and use up carbon dioxide, thanks

 

[Xayma]

They also must respirate.

Which also produces CO₂. Although I also suspect it has something to do with the basic nature of sea water which pushes the:

CO_2(g)+3H₂O_(l) <---> CO_2(aq)+3H₂O_(l) <----> H₂CO_3(aq)+2H₂O_(l) <---->CO₃^-2_(aq)+2H₃O⁺_(aq)

equilibrium to the right, which when tested will show a higher CO₂ conc.

 

[~*HSC 4 life*~]

depths greater than 100m im guessing?

havent started chemistry study yet :/

 

[xeriphic]

hmm I understand about the CO2 concentration now thanks

I checked the testbook and it said 500m - 1000m, not sure though since our teachers note were 50-100m lol

also could someone help me with this dot point

Explain that ship wrecks at great depths are corroded by electrochemical reactions and by anaerobic bacteria (anaerobic bacteria being the same as sulfate reducting bacteria ??)

 

[tennille]

Explain that ship wrecks at great depths are corroded by electrochemical reactions and by anaerobic bacteria (anaerobic bacteria being the same as sulfate reducting bacteria ??)

Yeah. The sulfate reducing bacteria are the anaerobic bacteria that cause the electrochemical reaction.

Reduction

SO42- + 5H2O + 8e- ---> HS- + 9OH-

Oxidation

Iron undergoes oxidation by bacteria:

4Fe ---> 4Fe2+ 8e-

Overall reaction =

4Fe2+ + SO4 + 5H2O ---> 4Fe2+ + HS- + 9OH- (1)

FE2+ reacts with HS- and OH- to form FeS and Fe(OH)2

4FE2+ + HS- + 7OH- ---> FeS + 3fE(OH)2 + H2O (2)

Therefore, the overall reaction is (1) + (2):

4FE2+ + SO42- + 5H2O ---> FeS + 3Fe(OH) + H2O + 2OH-

The rust is black iron (ll) sulfide along with iron (ll) hyroxide (which is not converted to iron (lll) since there is no oxygen)

 

[tina_goes_doo]

Wow. Your equations are completely different to mine. Here's what i got:


This corrosion is mainly caused by anaerobic bacteria which can reduce sulfate ions to sulfide. This reaction is usually done best in an acidic solution:
SO42-(aq) + 10H+ + 8e- --------> H2S(aq) + 4H2O(l)

Iron will undergo the oxidation reaction:
4Fe(s) --------> 4Fe2+ + 8e‾

Hence the overall equation:
4Fe(s) + SO42 + 10H+ ----------> H2S(aq) + 4Fe2+ + 4H2O(l)

After this step, the hydrogen sulphide forms an insoluble sulfide with metals.
Black iron(II) sulfide forms on the steel surface of submerged wrecks. Hydrogen ions are also released in this reaction:
H2S(aq) + 4Fe2+ ------------> FeS(s) + 2H+

Iron(II) ions can also react with water to form iron(II)hydroxide:
Fe2+ + 2H2O(l) --------> Fe(OH)2(s) + 2H+

As there is a low concentration of dissolved oxygen this far down in the ocean, normal rusting reactions do not occur and the Fe(OH)2 is not regularly converted into Fe2O3.H2O.


There are doubts as to how right that is. I looked in three different books and they all have different equations and processes. Me confused.

 

[xeriphic]

yer thanks both, I brought up the question because I was wondering about the equations too, for the reduction of sulfate, could anyone explain hmm

one I learnt from my teacher and the other came from the textbook

also though SO42-(aq) + 10H+ + 8e- --------> H2S(aq) + 4H2O(l) is the reduction process, where did the H+ originate from

 

[tennille]

The equations I have are from conquering chemistry. Maybe they're more complex or something...It doesnt really matter because even if it is wrong, you would have proof of where it's from and the HSC markers will mark it correct anyway.

 

[tina_goes_doo]

also though SO42-(aq) + 10H+ + 8e- --------> H2S(aq) + 4H2O(l) is the reduction process, where did the H+ originate from

Ok i'm still pretty confused as to which equations im using. Three people have now told me they use the one Tennille had down. Are they both right or what? And is hers the more common one?

But in reference to the equation above, i'm guessing the H+ is coming from the slightly acidic environment made by the anaerobic bacteria. Honestly don't quote me on that. I'm just guessing here. (now i feel stupid. I put down an equation and i forgot what it meant )

 

[xeriphic]

the H+ equation was the one offered by chemistry context, indeed now I'm confused, I'll ask my teacher or something

 

[tennille]

The final equation I had written down is incorrect. The equation was:

4FE2+ + SO42- + 5H2O ---> FeS + 3Fe(OH) + H2O + 2OH-

You wouldn't believe how many errors there are in Conquering Chemistry. I went on their website and they corrected it to:

4Fe + SO42- + 4H20 ---> FeS + 3Fe(OH)2 + 2OH- <---this is the correct equation

It is 4H20 not 5H20 and there is no H20 on the right.

The rest of the equations I previously typed are correct.

 

[tennille]

I think everyone is better off using tina_goes_doo's equations. They appear to make more sense than the one's I used from Conquering Chemistry. The equations don't even add up properly. It also explains how the acidic environment is produced whereas mine don't.

 

[xeriphic]

lol I'll ask the teacher about this when the tutorials is on

 

[Steven12]

SO42-(aq) + 10H+ + 8e- --------> H2S(aq) + 4H2O(l)

yea, i saw that equation many times, what i dont understand is. where did the 10H+ hydrogen originate in the first place?

 

[tennille]

SO42-(aq) + 10H+ + 8e- --------> H2S(aq) + 4H2O(l)

This reaction is favoured by acidic conditions, maybe that's where the H+ came from. I'm not completely sure though. The greater solubility of CO2 at greater depths perhaps is responsible for the H+.

 

[Xayma]

But a pH of 2 couldnt be accounted for if that much acid is being removed while only 6H⁺ are being released.

I suspect that the iron forms Iron II Hydroxide first creating a localised area of low pH around the wreck.

 

[Steven12]

suspect.... doesnt any text book confirm the origin of these H+ ions? I feel a bit stupid writing h+ ions, without explaining where they are from..

 

[Steven12]

suspect.... doesnt any text book confirm the origin of these H+ ions? I feel a bit stupid writing h+ ions, without explaining where they are from..

i mean, if what you said is true. then scientists WOULD expect ships to corrode at great depths since H+ions accelerate corrosion, and h ions can displace metals. most of them anyway