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(11)Gravimetry

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allelipraise's version from 2018-06-06 19:45

Section

Question Answer
Gravimetrybased upon the measurement of mass with the use of an analytical balance
Precipitation Methodsthe analyte is converted to a sparingly soluble precipitate. The precipitate is filtered, washed free of impurities, converted to a product o
Volatilization Methods the analyte or its decomposition products are volatilized in a suitable temperature
Colloidal Particleinvisible to the naked eye (10-7 to 10-4 m in diameter); low tendency to settle; not easily filtered
Crystalline Suspension particle size of 10-1 of a mm or greater; tends to settle spontaneously; readily filtered
Particle Growth- growth of precipitate on existing nuclei - formed at low relative supersaturation - promote formation of smaller number of large particles
Colloidal Precipitates- often stable for indefinite periods - stability can be destroyed by heating, stirring, or adding an electrolytecoagulation (more filterable form)
Nucleationfew particles come together to form a stable solid - these nuclei form on the surface of suspended solid contaminants
Peptization- process in which the colloidal particle reverts back to its dispersed state - particles “uncoagulate”
Digestion- process in which the precipitate is heated for a period of time - applicable for both crystalline and colloidal precipitates - weakly bound water is lost from the precipitate - gives denser mass which is easily filtered - “Ostwald ripening”
Coprecipitationprocess in which normally solule compounds are carried out of solution by a precipitate
Loss on Ignitionpercentage of the test material that is volatilized and driven off under the conditions specified
Ignite to Constant Weight the ignition shall be continued at 800 0C ± 25 0C unless otherwise indicated until consecutive weighings do not differ by more than 0.5 mg per gram of the substance taken (the second weighing following an additional 15-min ignition)
Loss on Drying determines the amount of volatile matter of any kind that us driven off under the conditions specified
Dry to Constant Weight the ignition shall be continued at 8000 ± 25 0C unless otherwise indicated until consecutive weighings do not differ by more than 0.5 mg per gram of the substance taken (the second weighing following an additional hour of drying)
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