Block 5: Chemical Speciation Flashcards
(20 cards)
What are complexes & how are they formed?
Complexes are central metal ions (+) surrounded by a ligand (- or neutral) in the electron donation process of ligand binding
What are the 3 primary chemical species?
Solutions are a homogenous mixture of solutes dissolved in a solvent
Colloids are substances consisting of microscopic particles substantially bigger than atoms or ordinary molecules
Particulates are complex mixtures of extremely small particles
How does ultra-centrifugation work?
High speed rotation separates heavier sediments out of solution
How do dialysis & ultra-filtration work?
Dialysis: a concentration gradient diffuses a solution through a semi-permeable membrane
Ultra-filtration: hydrostatic pressure pushes a solution through a semi-permeable membrane
What is the solubility product?
Ksp is the equilibrium constant for the dissolution of a solid substance in an aqueous solution, expressed as ion activities of products relative to reactants
What does solubility refer to?
The maximum amount of a substance dissolvable in a solvent
What does the law of mass action state?
That the rate of a reaction is proportional to the product of the concentrations of reactants over products
What is molal concentration & when does the chemical activity of an ion approach it?
Molal concentration is concentration per kg (as opposed to L for molar), which chemical activity approaches as the concentration of all solutes approaches zero, as attraction to lower solutes decreases electron availability
What variables does the activity coefficient relate? What do values signify? How is it calculated?
γ relates ionic activity to molal concentration (corrects for non-ideal behaviour)
γ = 0 means total chemical suppression, γ = 1 means total chemical uninhibition
γ is calculated using the Deibje-Huckel Theory
What does ionic activity represent?
I represents the effective concentration of species in solution, calculated by multiplying the actual concentration by the activity coefficient
What are the Pitzer equations?
The Pitzer equations calculate accurate activity coefficients in moderate to high ionic strength solutions, accounting for both short-range & long-range ion interactions
What is the ion activity product? When does IAP signify equilibrium
The ratio of ion activities of products to reactants in a current system
IAP = Ksp at equilibrium
How does the presence of ion pairs reduce the reactivity of individual ions in solution? What effect does this have?
Pairing lowers the reactivity of individual ions by lowering their activity coefficients & decreasing their free concentrations. This decrease in IAP can increase mineral solubility
What is the difference between dissolved & particulate solutions?
Dissolved constituents generally occur as ions electrostatically attracted to a pole of a water molecule
Particulate constituents are suspended within a liquid & can be physically separated out
What overall factors does chemical species define?
What is speciation?
Isotopic composition, electronic/oxidation state, complex/molecular structure
Speciation refers to the an element’s distribution among dissolved & particulate phases in a system
Why does heating a system decrease gas solubility?
Gas dissolution is exothermic, and increasing temperature will shift the system to reverse the change (Le Chatelier), favouring the endothermic degassing reaction
What is ionic potential & how does it affect solubility?
Ionic potential is the ratio of ionic charge: ionic radius
Higher ratios indicate lower solubilities
What is the adsorption edge?
The threshold of pH in which there is a large shift in adsorption of heavy metal ions
How does the adsorption of cations & anions change with increasing pH?
Cations: adsorption increases as high OH- availability means surfaces are negatively charged
Anions: adsorption decreases as low H+ availability means surfaces are negatively charged
What do the linear, Langmuir, & Freundlich adsorption isotherms account for/assume?
Linear: adsorption is directly proportional to concentration
Langmuir: adsorption occurs on finite sites
Freundlich: adsorption increases with concentration but rate decreases over time
