Example reactions for chemical weathering (4-Provenance)

simple solution, hydrolysis, oxidation/reduction, hydration/dehydration

what must simple solution have?

no mineral produced

what must hydrolysis have?

an OH attached to something

what must hydration have?

mineral produced

what must redox have?

ion that changes its charge

SiO2 + 2H2O → H4SiO4

simple solution

why is the simple solution one simple solution and not the others?

hydration would have OH added to something, hydrolysis would have a mineral be produced (not an acid)

2KAlSi3O8 (s) + 2H+ +9H2O → Al2Si2O5(OH)4 (s) + 2K + 4H4SiO4

hydrolysis

what are the minerals in the hydrolysis example?

potassium feldspar and kaolinite

what is the general formula for feldspar?

Si3O8

what is important about the hydrolysis example?

it involves clay, which is hydrated by definition, but the reaction is not hydration

where does that particular hydrolysis reaction happen often?

weathering process in humid environment

what is the general formula for clay mineral?

(Na,Ca)(Al,Mg)SiO(OH)

CaCO3 (s)+ H2O + CO2 (g) → Ca2+ + 2HCO3-

simple solution

what is CaCO3? more?

calcite, main constituent of limestone

what reaction do limestones undergo at the surface?

simple solution

Fe2O3 (s)+ H2O → 2FeO*OH

oxidation

what must you do to determine redox?

look at the charge of the cation (or anion)

what is a common surficial reaction?

oxidation of iron

what is FeS2?

pyrite

what is Fe2O3

hematite

CaSO4*2H2O → CaSO4 (s)+ 2H2O

dehydration

what is CaSO4×2H2O

gypsum

what does gypsum turn into? how?

anhydrite, dehydration

(Mg, Fe)2SiO4 + 4H+ → 2(Mg, Fe)2+ + H4SiO

simple solution

what is the general formula for olivine?

(Mg, Fe)2SiO4

what does it mean if silicic acid is the product?

simple solution, bc its not a new mineral

Mg2SiO4 + 4H2O → 2Mg(OH)2 + H4SiO4

hydrolysis

what is Mg2SiO4?

forsterite, pure magnesium form of olivine

what is 2Mg(OH)2?

brucite