For the questions, see Shipwreck: science to the rescue!
Two pathways are common: to hydrated iron(II) sulphate:
FeS2(s) + 7/2O2 + (n+1)H2O → FeSO4·n(H2O)(s) + H2SO4(aq)
or to goethite, alpha-FeOOH (as in rust):
FeS2(s) + 15/4O2 + 5/2H2O → FeOOH(s) + 2H2SO4(aq)
Answer: 1000 kg S corresponds to 15.6 kmol FeS2. If hydrated iron(II) sulphate is the end product, 1.5 tonnes sulphuric acid would form. If goethite, alpha-FeOOH, forms, the amount would be double: 3.1 tonnes sulphuric acid.
Answer: To neutralise 1.5 tonnes sulphuric acid, 2.6 tonnes sodium bicarbonate would be required; 3.1 tonnes of sulphuric acid would require 5.2 tonnes of sodium bicarbonate.
Estimate how many times the volume will increase when a pyrite crystal oxidises and a) FeSO4·7(H2O)(s), b) FeSO4·4(H2O)(s) or c) NaFe3(SO4)2(OH)6 salts crystallise as products. What effects could these processes have if they took place inside the wood structure?
Answer: When solid FeSO4·7(H2O)(s) precipitates, the volume increases with a factor of 12.2 for FeSO4·7(H2O)(s); 8.1 times for FeSO4·4(H2O)(s); and 6.7 times for NaFe3(SO4)2(OH)6. This can cause outbursts of salts through the wood surface, or crack the wood structure from within.
Answer: The O2 molecule is paramagnetic with the two outermost electrons unpaired, one in each of two degenerate (with same energy) anti-bonding molecular π-orbitals formed by combining the p-orbitals of the O atoms. With an energy uptake of ~92 kJ mol-1 from photons of light, the two outermost electrons can be paired (a 400-nm photon has energy of 300 kJ mol-1). The energy uptake process usually needs a sensitiser (e.g. light-absorbing dissolved organic matter). This excited singlet 1O2 (one single arrangement in space for a pair of electrons) oxygen molecule is a diamagnetic but reactive short-lived species, even though its energy is only sufficient for mild oxidation (Stumm W, Morgan J (1996) Aquatic Chemistry (3rd ed). New York, NY, USA: Wiley-Interscience).