Gravimetric Methods Flashcards
Any method in which the signal is mass or change in mass
Gravimetry
One gravimetric method wherein the signal is mass of a precipitate
Gravimetric precipitation
_____ occurs upon the addition of the first drops of the precipitating agent, then nucleation starts to occur where molecules of precipitating aggregate.
Supersaturation
According to this relation, the osrticle size is inversely proportional to a quantity called relstive supersaturation
von Weimarn ratio
To prevent particle growth instead of further nucleation, the ratio must be kept high. True or false.
False, low
Suspensions consist of tiny particles with diameters of 10^-7 to 10^-4 cm. Theys how no tendency to settle fron solution abd are difficult to filter
Colloidal suspension
Suspensions composed of particles with diameter larger than 10^-4 cm. They tend to settle spontaneously and are easily filtered
Crystalline suspension
Occurs when smaller particles clump together to form larger particles
Coagulation
Process that involves dissolution of small particles and reprecitation on larger ones resulting in particle growth and better particle characteristics
Ostwald Ripening
One form of contamination of gravimetric precipitates
Coprecipitation
Which of the ff is not an example of coprecipitated impurities
Inclusion
Occlusion
Exclusion
Surface adsorption
Mixed crystal formation
Mechanical entrapment
Exclusion
____ is the impurity adsorbs to the surface of a precipitate. Corrected by ,____
Surface adsorption, washing
____ is when impurities trapped within the precipitate as it forms. Corrected by ____
Occlusion, digestion
____ refers to when the interfering ion occupies a lattice site in the precipitate
Corrected by ___
Inclusion, reprecipitate
____ is when one of the ions in crystal lattice of solid is replaced by an anion
Mixed crystal formation
Occurs when crystal lie close together during growth
Mechanical entrapment
Gravimetric method wherein the signal is the loss of a volatile specie
Volatilization gravimetry
Gravimetric method wherein the signal is the mass of wn electrideposit on the electrode in a electrochemical cell
Electrogravimetry
Gravimetric method wherein the mass of sample is measured over time as the temperature changes
Thermogravimetry
Gravimetric method wherein the mass of sample is measured over time as the temperature changes
Thermogravimetry
Characteristics of a gravimetric precipitating agent
1 react specific/selective with analyte
2 Easily filtered
3 Washed free of contaminants
4 Unreactive with constituents of atmosphere
5 insoluble
6 larger particle size
Process of precipitation gravimetry
Taring crucibles
Weighing of sample
Dissolution of sample
Precipitation of analyte
Digestion
Filtration
Ignition
Weighing of residue
During ___ precipitate is heated in the mother liquor and allowed to stand in contact with solution
Digestion
Mother liquor is a soition from whuch a precipitate was formed
Mechanism of precipitate formation
- Nucleation (particles diameter of 10^-7 to 10^-4 cm)
- Particle growth (particles diameter of greater than 10^-4 cm)
Recall the optimum conditions for precipitation that will keep the ratio low to promote particle growth instead of further nucleation
S-equilibrium solubility
Q-concentration of solute
Increase S by precipitation from hot solution
Adjust pH of precipitating medium to imcrease S
Precipitation using dilute solution to decrease Q
Slow addition of precipitating agent decrease Q
Stirring the solution during addition of precipitating agent to keep Q as low as possible
Generally keep S high, Q low
Recall the optimum conditions for precipitation that will keep the ratio low to promote particle growth instead of further nucleation
S-equilibrium solubility
Q-concentration of solute
Increase S by precipitation from hot solution
Adjust pH of precipitating medium to imcrease S
Precipitation using dilute solution to decrease Q
Slow addition of precipitating agent decrease Q
Stirring the solution during addition of precipitating agent to keep Q as low as possible
Generally keep S high, Q low
Colloids are best precipitated from hot, stirred solutions containing sufficient electrolytes to ensure coagulation
True
Colloid layers
Primary adsorptive layer
Secondary layer (counter layer)
High concentration, +
Low concentration, -
Precipitation occurs in solution rich in dissolved solids so the initial precipitate is often impure
True
One of the most accurate and precise methods of macro quantitative analysis
Gravimetric analysis
Gravimetry DOES NOT require a series of standards for calculation of an unknown since calculations are based only on atomic or molecular weights
TRUE
