Gravimetric Methods Flashcards

1
Q

Any method in which the signal is mass or change in mass

A

Gravimetry

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2
Q

One gravimetric method wherein the signal is mass of a precipitate

A

Gravimetric precipitation

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3
Q

_____ occurs upon the addition of the first drops of the precipitating agent, then nucleation starts to occur where molecules of precipitating aggregate.

A

Supersaturation

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4
Q

According to this relation, the osrticle size is inversely proportional to a quantity called relstive supersaturation

A

von Weimarn ratio

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5
Q

To prevent particle growth instead of further nucleation, the ratio must be kept high. True or false.

A

False, low

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6
Q

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

A

Colloidal suspension

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7
Q

Suspensions composed of particles with diameter larger than 10^-4 cm. They tend to settle spontaneously and are easily filtered

A

Crystalline suspension

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8
Q

Occurs when smaller particles clump together to form larger particles

A

Coagulation

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9
Q

Process that involves dissolution of small particles and reprecitation on larger ones resulting in particle growth and better particle characteristics

A

Ostwald Ripening

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10
Q

One form of contamination of gravimetric precipitates

A

Coprecipitation

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11
Q

Which of the ff is not an example of coprecipitated impurities

Inclusion
Occlusion
Exclusion
Surface adsorption
Mixed crystal formation
Mechanical entrapment

A

Exclusion

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12
Q

____ is the impurity adsorbs to the surface of a precipitate. Corrected by ,____

A

Surface adsorption, washing

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13
Q

____ is when impurities trapped within the precipitate as it forms. Corrected by ____

A

Occlusion, digestion

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14
Q

____ refers to when the interfering ion occupies a lattice site in the precipitate
Corrected by ___

A

Inclusion, reprecipitate

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15
Q

____ is when one of the ions in crystal lattice of solid is replaced by an anion

A

Mixed crystal formation

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16
Q

Occurs when crystal lie close together during growth

A

Mechanical entrapment

17
Q

Gravimetric method wherein the signal is the loss of a volatile specie

A

Volatilization gravimetry

18
Q

Gravimetric method wherein the signal is the mass of wn electrideposit on the electrode in a electrochemical cell

A

Electrogravimetry

19
Q

Gravimetric method wherein the mass of sample is measured over time as the temperature changes

A

Thermogravimetry

20
Q

Gravimetric method wherein the mass of sample is measured over time as the temperature changes

A

Thermogravimetry

21
Q

Characteristics of a gravimetric precipitating agent

A

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

22
Q

Process of precipitation gravimetry

A

Taring crucibles
Weighing of sample
Dissolution of sample
Precipitation of analyte
Digestion
Filtration
Ignition
Weighing of residue

23
Q

During ___ precipitate is heated in the mother liquor and allowed to stand in contact with solution

A

Digestion
Mother liquor is a soition from whuch a precipitate was formed

24
Q

Mechanism of precipitate formation

A
  1. Nucleation (particles diameter of 10^-7 to 10^-4 cm)
  2. Particle growth (particles diameter of greater than 10^-4 cm)
25
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
26
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
27
Colloids are best precipitated from hot, stirred solutions containing sufficient electrolytes to ensure coagulation
True
28
Colloid layers Primary adsorptive layer Secondary layer (counter layer)
High concentration, + Low concentration, -
29
Precipitation occurs in solution rich in dissolved solids so the initial precipitate is often impure
True
30
One of the most accurate and precise methods of macro quantitative analysis
Gravimetric analysis
31
Gravimetry DOES NOT require a series of standards for calculation of an unknown since calculations are based only on atomic or molecular weights
TRUE