Gravimetric Methods of Analysis (PART 1) [Sir Jameso PPT] Flashcards
Gravimetric methods of analysis are based on determining the ______ of a pure compound to which the analyte is chemically related.
mass
There are two major types of gravimetric methods:
precipitation methods and volatilization methods.
In _________, the analyte is converted to a sparingly soluble precipitate.
precipitation gravimetry
This precipitate is then filtered, washed free of impurities, and converted to a product of known composition by suitable heat treatment, and the product is weighed.
precipitation gravimetry
In ___________, the analyte or its decomposition products are volatilized at a suitable temperature.
volatilization gravimetry
The volatile product is then collected and weighed, or, alternatively, the mass of the product is determined indirectly from the loss in mass of the sample
volatilization gravimetry
The ideal precipitating reagent would react with the analyte to give a product that is
- Readily filtered and washed free of ______
- Of sufficiently _________ so that no significant loss of the solid
occurs during filtration and washing - Unreactive with constituents of the __________
- Of known composition after it is dried or, if necessary, ________
contaminants
low solubility
atmosphere
ignited
Precipitates made up of ____ are generally desirable in gravimetric work because large particles are easy to filter
and wash free of impurities.
large particleslarge particles
a solid made up of particles having diameters that are less than 10-4 cm.
colloid
It show no tendency to settle from solution, nor are they easily filtered.
Colloidal particles
The particles, with dimensions on the order of tenths of a millimeter or greater, temporarily dispersed in the liquid phase is called a _________
crystalline suspension
The particles of a ________suspension tend to settle spontaneously and are readily filtered.
crystalline
the concentration of the solute at any instant and S is its equilibrium solubility.
Q
What Factors Determine Particle Size?
When (Q - S)/S is large, the precipitate tends to be _____
colloidal
What Factors Determine Particle Size?
When (Q - S)/S is small, a ______ is more likely.
crystalline solid
How Do Precipitates Form?
Assume that precipitates form in two ways, namely by ______and by ________
nucleation
particle growth
How Do Precipitates Form?
The particle size of a freshly formed _____________is determined by which way is faster.
precipitate
a process in which a minimum number of atoms, ions, or molecules join together to produce a stable solid.
Nucleation
the individual particles of most colloids to give a filterable, amorphous mass that will settle out of solution.
Coagulate, or agglomerate
It can be hastened by heating, stirring, and adding an electrolyte to the medium.
Coagulation
a process in which a substance (gas, liquid, or solid) is held on the surface of a solid.
Adsorption
In contrast, ______involves retention of a substance within the pores of a solid.
absorption
a process by which a coagulated colloid returns to its dispersed state.
Peptization
a process in which normally soluble
compounds are carried out of solution by a precipitate.
Coprecipitation
a common source of coprecipitation that is likely to cause significant contamination of precipitates with large specific
surface areas, coagulated colloids.
Surface Adsorption
A drastic but effective way to minimize the effects of adsorption is reprecipitation, or double precipitation.
Reprecipitation
a type of coprecipitation in which a compound is trapped within a pocket formed during rapid crystal growth.
Occlusion
_______ entrapment occurs when crystals lie close together during growth.
Mechanical
is often remarkably helpful in reducing these types of coprecipitation.
digestion
a process in which a precipitate
is formed by slow generation of a precipitating reagent homogeneously throughout a solution.
Homogeneous precipitation
After filtration, a _______ is heated until its mass becomes constant.
gravimetric precipitate
Some precipitates are also ________to decompose the solid and form a compound of known composition.
IGNITED
This new compound is often called the
weighing form
Recording thermal decomposition curves is often called _____ or thermogravimetric analysis, and the mass vs. temperature curves are called ______________.
thermogravimetry
thermograms
Numerous ______ reagents have been developed for the gravimetric determination of inorganic species.
organic
One forms slightly soluble nonionic products called ________
coordination compounds.
The other forms products in which the bonding between the inorganic species and the reagent is __________ ionic
largely
cyclical metal-organic compounds in which the metal is a part of one or more five- or six-membered rings.
Chelates
_______ and _________are two widely used chelating reagents.
8-Hydroxyquinoline
dimethylglyoxime
__________ tetraphenyl borate is a near-specific precipitation agent for potassium and ammonium
Sodium
is spectacular in appearance since it has a beautiful vivid red color
Nickel dimethylglyoxime
is an important example of an organic precipitating reagent that forms salt-like precipitates
Sodium tetraphenylborate, (C6H5) 4BNa+
The two most common gravimetric methods based on volatilization are
those for ____and carbon dioxide.
water
carbon dioxide.
are ordinarily decomposed by acids to give carbon dioxide, which is readily evolved from solution by heat.
Carbonates
