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15
CH3041
SILICON &
ALUMINIUM
• Si
27.7% and Al 8.1% are abundant in the
crust yet neither are abundant in river water.
crust yet neither are abundant in river water.
• Si is present as silicic acid H4SiO4 , conc.
is low as silicate minerals weather slowly.
They are 3-D network covalent solids.
is low as silicate minerals weather slowly.
They are 3-D network covalent solids.
• Al only moves into the water column when
the pH is either high or low.
Al(OH)3(s) D Al3+ + 3OH- low pH
the pH is either high or low.
Al(OH)3(s) D Al3+ + 3OH- low pH
(Gibbsite) Al(OH)3(s) + OH- D Al(OH)4- high pH
• Aluminium is insoluble at normal pH 5.5 -
9
• Al3+ is a
strong Lewis acid &
releases H+
from coord water. [Al(H2O)5(OH)]2+ + H+
from coord water. [Al(H2O)5(OH)]2+ + H+
• Al3+ is quite toxic to fish.
