2006 paper microenvironments? (1 Viewer)

[Sassed]

Hey just wondering if anyone would be able to assist me with question 30
b) (iii) Microenvironments are localised areas where conditions are different from those in surrounding areas.
Explain the effect of each microenvironment on the rate of corrosion of the iron ship. Include at least one balanced chemical equation in your answer.
(there is an image of ship, fully submerged with labelled acidic microenvironment and sulfate-reducing bacteria microenvironment).
It's a 3 mark question and I get the general gist of what I need to write but wondering if there are any specifics I need to include?
Thank you for any help

 

[liamh16]

Here's some info off the top of my head;



Acidic conditions are caused by certain bacteria which produce H+ ions in their normal metabolism. These bacteria can feed off materials found in and around the shipwreck such as fabrics and timber, which accelerates the rate of the production of the bacteria, and then you end up with slightly acidic conditions because you have alot of bacteria producing the H+ causing an acidic microenvironment. This accelerates the rusting because due to the presence of H+ ions the reduction half equation shifts from 1/2 O2 + H20 + 2e- --> 2OH- 0.40V to 1/2 O2 + H+ + 2e- --> H2O. This reaction readily occurs in acidic conditions, and the electrode potential increases as the acidity increases thus the half equation has more tendancy to occur in the acidic conditions. THUS the corrosion is accelerated.

Sulfate Reducing Bacteria also increase corrosionm by the bacteria reducing from sulfate to sulfur

SO4(aq) -> S2-(aq) + 2O2(g)
Fe2+(aq) + S2-(aq) -> FeS(s)

This gives off O2 gas to the microenvironment which accelerates rusting.
SRB also form fingers of reddish brown growth called rusticles that hang from steel structures like small stalactites e.g. FeO and FeSO4
As a result of this microenvironment, the corrosion is accelerated due to the O2 produced, as well as rusticles forming greatly detriorating the state of the ship.



Hope that helped