di) Remember – we cleaned, dried & weighed all the identical samples. Then submerged them in pH buffers acidic (pH <7), neutral (pH =7) and basic (pH > 7). We observe the rate of corrosion via bubbling and colour of solution and by cleaning, drying and weighing at the end (basic = no corrosion (passivating), neutral = normal rust, acidic = no rust but iron dissolved = large mass loss.
dii) Remember that there are two reasons why metals corrode more in acidic environments i) MASH – hydrogen ions oxidize reactive metals (any metal with a –ve reduction potential). ii) Oxygen is a stronger oxidant in acidic conditions (give two oxygen reduction potential equations from the data sheet to prove) thus the rate of corrosion is higher.
2004
dii) Remember
the experiment was as described in 2002di) above but we changed the oxygen
concentration via having i) partially submerged, fully submerged, fully
submerged with oil layer on top, fully submerged in pre-boiled water with oil
layer on top. We observed qualitatively for the time until first sign of
corrosion and fr the extent corrosion at the end of the experiment.diii) To explain differences in rusting you must include the rusting equations. Even though the sunk ship is submerged the ship on the shore would be constantly wet and salty (perhaps even higher salt conc due to evaporation) so they both have an electrolyte. The temperature and oxygen concentration of the shore ship would be higher. Thus the shore ship rusted faster (as shown in the pic) NOTE – 30m is NOT deep enough for SRB and acidic microenvironments to have an impact. But you should explain why its temp and oxygen is lower (ie water high heat capacity keeps the ocean cooler and oxygen has low solubility in water as it is non-polar).
2006
bi) Yes
CO2 is more soluble that oxygen in the water but it is OXYGEN that
is the oxidant in rusting.bii) Be careful how you express yourself. Low temperatures and high pressures make gases MORE SOLUBLE. But (just like the deep ocean) low tem and high pressure does not mean that there will be ‘more dissolved’ gas.
2007
ci) See
2002 di above
2010
di) As
described in 2004 dii) above except we also changed oxygen concentration, salt
concentration (and pH) in three different experiments. Temp was changed via use
of incubator, room temp, fridge and freezer (but problems…). Oxygen conc and pH
as described in 2004 dii) & 2001di). If weighing – make sure you clean dry
and weight then after the experiment, wipe off the corrosion product, clean,
dry and weigh AND say the larger the mass loss the greater the rate of
corrosion.dii) keep it simple – to keep the electrolyte or oxygen away from the steel – paint! (or use some other barrier protection) – 1 mark = keep it simple
2012
ci) The
conditions would be anaerobic conditions where there are sulphate ions where
SRB live = eg deep ocean
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