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47 Cards in this Set
- Front
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Gravimetric methods
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methods that depend upon measuringmass
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Precipitation methods
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The species to be determined isprecipitated by a reagent that yields a sparingly soluble product (a product of known composition, or a product that can beconverted to one of known composition).ȗ;�OAg�
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Volatilization methods
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theanalyte is separated from other sample constituents by converting it to a gasof known composition. The analyte (or its decomposition products) arevolatilized at a suitable temperature. The volatilized species are collectedand weighed directly or weighed by difference.
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Electrogravimetry |
The analyte is separated by deposition on an electrode by an electrical current |
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gravimetric Titrimetry |
the mass of a reagent of known concentration required to completely react with the analyte provides the information needed to determine the analyte concentration |
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Atomic mass spectrometry |
uses a mass spectrometer to separate the gaseous ions formed from the elements making up a sample of matter |
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The idealprecipitating agents is one that reacts with one and only oneanalyte to produce as solid that is ...
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Low in solubility easily filterable Unreactive to the atmosphere of known composition large particle sizes work best |
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Colloidal Suspensions |
Suspension whose particles are invisible to the naked eye 10-7 to 10-4 |
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Colloid |
Consist of solid particles with diameters that are less than 10-4 in size Low solubilities best precipitated from hot stirred solutions |
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Crystalline suspension |
particles bigger in size and are easier to settle and are readily filterable |
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Tyndall Effect |
movie example. When particles scatter visible radiation |
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Particle size of a precipitate is influenced by |
precipitate solubility temperature reactant concentrations rate at which the reactants are mixed |
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Relative supersaturation |
The net effect of all the variables that can be qualitatively accounted for Q (concentration of solute)- S (equilibrium solubility) / S (equilibrium solubility) |
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Large/ High Relative Supersaturation corresponds to |
Colloidal precipitate Nucleation Mechanism Large number of small products formed |
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Small Relative Supersaturation |
Crystalline Sold precipitate Particle Growth Mechanism Small number of larger particles |
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supersaturated solution |
an unstable solution that contains a higher solute concentration than a saturated solution |
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Nucleation |
Process in which a minimum number of atoms, ions, or molecules join together to give a stable solid. If dominates a large number of small particles results Formation in a supersaturated solution of the smallest precipitate particles capable of spontaneous growth |
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Particle Growth |
Deposition of ions/ molecules on the surface of the solid nucleated particles If dominates, a small number of larger molecules results |
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Adsorption |
The process in which a substance is held on a surface of a solid |
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Absorption |
retention of a substance within the pores of a solid |
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Coagulation/ Agglomerarion |
the process by which colloidal particles coalesce to form larger aggregates Can be hastened by heating, stirring, and adding an electrolyte to the medium Increasing particle size |
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Colloidal suspensions are stable because |
all of the particles are positively or negatively charged |
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Primary adsorption |
Charged layer of ions on the surface of a solid |
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Counter Ion Layer |
Layer that surrounds the charged particle layer that consists of an excess of negative ions to balance the charge on the surface of the particle |
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Electric Double Layer |
layer formed of the primary layer and the counter ion layer that provides stability to the colloidal suspension |
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Increasingthe electrolyte concentration hasthe effect of decreasing the volume of the counter ion layer, thereby
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increasing the chances for coagulation
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Peptization |
the process by which a coagulated precipitate is returned to is colloidal state |
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Peptization can be caused by |
Washing away electrolytes responsible for coagulation, increase the volume of the counter ion layer Washing away colloidal pieces of the precipitate |
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Peptization can be minimized by |
Washing a precipitate with a solution of an electrolyte that is volatilized during an ensuing drying step |
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Digestion |
the process in which a precipitate is heated in the solution from which it was formed and allowed to stand in contact with the solution expels water from the crystal producing a denser better filtering precipitate |
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Mother Liquid |
the solution from which a precipitate is formed |
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Co-precipitation |
process in which normally soluble compounds are carried out of a solution by a precipitate |
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4 types of Co-precipitation |
Surface Adsorption Mixed crystal formation occlusion Mechanical Entrapment |
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Surface adsorption (equilibrium process) |
Causes contamination of precipitates with large surface areas like coagulated colloids |
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Specific surface area |
The surface are per unit mass |
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Mechanical entrapment (kinetic) |
when two crystals grow together and trap a species in the space between them |
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Occulsion (kinetic) |
A compound is trapped within a pocket formed during rapid crystal growth |
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Mixed Crystal Formation (equilibrium) |
co precipitation formed when one of the ions in the crystal lattice are replaced by an ion of another element |
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Reprecipitation |
used to minimize adsorption process by which the the filtered solid is redissolved and re precipitated Lower contaminant concentration |
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Co-precipitation is reduced by |
Using dilute solutions Rapid filtration Removing undesired ions before precipitaion |
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Post precipitation |
Theprecipitate causes a localized high concentration of unwanted species.
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Drying
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removesthe solvent(s) of the mother liquid from which the precipitate was formed.
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Ignition
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converts the precipitate to a known composition called the weighing form.
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Homogenous precipitation |
Technique in which a precipitating agent is generated in a solution of the analyte by a slow chemical reaction |
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Thermogravimetric analysis
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substance is heated and its mass is measured as a function of temperature.
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Coordination compounds |
species formed when between metal ions and electron pair donating groups. |
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Chelating agents |
Substances with multiple sites available for coordinate bonding with metal ions. products called chelates |