chapter 4 a & b Flashcards
small particles of matter
tremendously high specific areas
seat of chemical activities in the soil
soil colloids
stable, minute, and complex organic particles resulting from biological decomposition of organic residues
organic colloids
very fine clay components
inorganic colloids
kaolinite, montmorillonite, illite, and vermiculite
silicate clay
why are they called silicate clays
chemical structure is made up of silicon and aluminum
silicon at the center, surrounded by oxygen and hydroxyl atoms
tetrahedron
silica and alumina layers or sheets are bound by shared oxygen atoms
octahedron
1:1 non expanding
kaolinite (antipolo)
2(tetra):1(octa) expanding
montmorillonite (binangonan)
characteristics of kaolinite
low
- specific surface area
- sorption capacity
- plasticity
- shrink-well capacity
characteristics of montmorillonite
high
- specific surface area
- sorption capacity
- plasticity
- shrink-well capacity
sources of negative charge for silicate clays
exposed hydroxyl groups at the broken edges of crystals; exposed oxygen contributes to the negative charge
H of the hydroxyl dissociates, esp. at high pH. (amt of (-) charge depends on pH: “pH dependent charge)
isomorphous (same size) substitution in the silica or octahedral sheets)
explain ion replacement
replace of an ion the crystal lattice by another ion of about the same size.
- Si, Al, and Mg have almost the same size (0.41, 0.5, 0.65)
charges from the isomorphous sub are permanent charges and don’t depend on pH
- typical of vermiculite and montmorillonite
how organic colloids contribute to chemical property of soils
humus is not crystalline, unlike clays, but also has the same specific surface area.
- dissociation of H+ from the carboxylic (-COOH) and phenolic (<- -> OH) functional groups at high pH
humus , like mont clay, enable the soil to have greater ability to absorb and exchange ions.
which clay does have a hydrogen bonding and does not
have: kaolinite
doesn’t: montmorillonite
groups of clay colloids
crystalline silicate
crystalline non-silicate (Fe/Al oxide or sesquioxides)
amorphous silicate
amorphous non-silicate (Fe/Al oxide or sesquioxides)
crystalline silicate
sheet-structures alluminosilicates depending on ratio of silica sheets to alumina sheets
- 1:1non-expanding: kaolinite
- 2:1 expanding: montmorillonite
- 2:1 limited expansion: vermiculite
- 2:1 non-expanding: illite
- 2:1:1 chlorite
amorphous silicate
allophane and imogolite
in PH, relatively young soils derived from volcanic ash and high OM
amorphous non-silicate
amorphous hydrous oxides of Fe/Al
ability of soil to absorb and exchange cations with the soil solution and plant roots
cation exchange capacity
sum of negative charges of the soil
cec
what attract cations
net negative charges or those not neutralized by + charges
CE reactions in soils are
instantaneous, reversible, and stoichometric
units of cec
cmolc / kg (centimol + charge per kg soil)
meq / 100g (milli-equivalentper 100 g of soil)
