(F) Gravimetric method of analysis Flashcards
Based on measuring the mass of a pure compound though which the analyte is chemically related.
Gravimetric Analysis
analyte is separated from solution of sample as a precipitate converted to a compound of known composition that can be weighed.
Precipitation Gravimetry
analyte is separated from other constituents by conversion to gas, and the weight of the gas is used as a measure of analyte concentration
for substances thar evaporate or are volatile
volatilization gravimetry
analyte is separated by deposition on an electrode via electrical current
Electrogravimetry
changes in physical and chemical properties of materials are measured as a function of increasing temperature or as a function of time
Thermogravimetry
T of F : You’re supposed to wash colloidal precipitates like crystalline precipitates
F you do NOT wash them because peptization occurs
The conversion of precipitate into colloidal solution by adding a suitable electrolyte
peptization
T or F : it is not ideal to have low solubility in a precipitate
false it is ideal so that your precipitate won’t dissolve as you are filtering it
T or F : it is ideal that your precipitate is free of contaminants and be bigger in size
T
T or F : The more reactive your precipitate is the better
False it is better if it is stable and unreactive with the constituents of the atmosphere
The net effect of these variables that determine the particle size can be accounted for relating the particle size to a single property
relative supersaturation by von weimarn, 1925
unstable solution that contains a higher solute concentration than a
saturated solution. As excess solute precipitates with
time, supersaturation decreases to zero.
supersaturated solution
T or F : if Ksp > Qsp = precipitation will not happen
F it will
T or F : If supersaturation decreases to zero, precipitation
will also stop.
T
measure of the solute’s
supersaturation.
Q - S
Q= concentration of the solute
Idk what the S is i cant find it sorry
T or F: The relationship between the value of RSS and the
particle size is DIRECTLY PROPORTIONAL. As the
value of RSS increases, the particle size decreases, and
vice versa.
F (inversely)
process of forming smaller particles or colloidal
particles.
NUCLEATION.
T or F: The RSS value is BIG . A solution must have a low
supersaturation which would mean that the precipitate will be larger in terms of the particles.
F (its smol like my brein)
The initial formation process in which
a minimum number of atoms, ions, or molecules join
together to give a stable solid.
NUCLEATION
2 types of nucleation
sponataneous and induced
The subsequent growth after
nucleation. It means building of nuclei over each other
which will eventually form a crystalline solid.
PARTICLE GROWTH:
are precipitants that creates complex
ions.
(Complexing
agents
happen when you add
an organic precipitant in the solution and
creates complexes with the metallic ion.
Complex ions
metallic ion will be
part of the central atom/structure of the
precipitate and around the central atom/metallic ion, there will negative charges
contributed by the organic complexing agent.
It increases solubility of precipitate as well.)
Complexes
T or F : We use a concentrated solution in a precipitating process
False we dont
Tor F; To decrease Q , we use the homogeneous precipitation technique
T
This is when particles collide but do
not interact. It is not affected by gravity.
Brownian movement
does not settle out of solution due to its size and Brownian movement
Colloids
Accumulation and building up
coagulation
same as coagulation but involves a combination of a larger froup of different ions/ atoms with each other
Agglomerate
T or F: coagulation may be hastened by cooling, digestion and adding an electrolyte
F (it will be hastened by heating in a water bath, stirring, and adding an electrolyte)
T or F :Colloids are stable due to being either a negative and positively charged particles
T
components of electric double layer
primary adsorption layer and counter ion layer
a layer in the electric double layer that consists mainly of adsorbed silver ions
primary
A process in which a substance (gas,
liquid, or solid) is held on the surface
of a solid.
ADSORPTION
A process in which a substance
within the pores of a solid.
ABSORPTION
a layer in the electric double layer that contains sufficient
excess of negative ions (principally nitrate) to just
balance the charge on the surface of the particle.
counter - ion layer
T or F : as colloid particles approach each other, the electric double layer produces an electrostatic force, preventing panicles from adhering or colliding
T
measure of repulsive force that particle exerts on like particles in the solution
Effective charge (q)
T or F : More diluted means that there is more distance for forces of agglomeration
F less distance
T or F : Increased heat decreases absorbed ions
F increases
these are bigger particles, easily filtered and are purer
Crystalline
T or F : Crystalline formation can be improved significantly by minimizing Q and maximizing S in the RSS value or von weirman equation
T
T or F: effective charge should be reduced to zero to increase repulsive forces, making it easier to coagulate
F (decreases repulsive force)
main cause of impurities -
process where normally soluble compounds are carried out of solution by a precipitate and may result in impurities and / or contamination
coprecipitation
process where a foreign compound precipitates on top of the desired precipitate
post precipitation
major source of contamination in coagulated colloids du to impurity being chemically or physically adsorbed on the surface of precipitates
surface adsorption
T or F: by using volatile electrolytes, this increases surface adsorption
false decrease
occurs when exchange of two ions that have the same charge, roughly about the same size (>5%), belongs to the same crystal class
mixed crystal formation
T or F: changing to a more selective precipitating agent reprecipitation minimizes mixed crystal formation
T
Greatest type of co-precipitation ni which a compound (freign ions in the counter-ion layer) is physically trapped within a precipitate during rapid precipitate formation
Occlusion
A type of co-precipitation in which coprecipitates physically trap a pocket of solution within a precipitate during rapid precipitate formation.
Mechanical Entrapment
process which a precipitate is formed by slow generation of a precipitating reagent homogeneously throughout a solution (therefore excesses do not occur)
Homogeneous Precipitation
T or F : Solids formed by homogeneous precipitation are purer but smaller in size
F (larger)
complexing agent, increasing purity and decreases the unwanted compounds / contaminants
urea
reagents that form coordination compounds
and prevents formation of unwanted side products
chelating agents
special type of ligand that can form multiple bonds to the metal ion resulting to a highly stable compound, highly colored coordination
chelates
bonds to the central metal ion, donates electrons to the metal ion (chelating agents)
ligands
creates complexes / chelates with nickel ion
normally forms red complex solution (cherry red) light green to dark red precipitate
can be enhanced by turning it slightly basic (add basic solns 8-10)
Dimethylglyoxime
