Gravimetric Methods

Question 1

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

Answer 1

Gravimetry

Question 2

One gravimetric method wherein the signal is mass of a precipitate

Answer 2

Gravimetric precipitation

Question 3

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

Answer 3

Supersaturation

Question 4

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

Answer 4

von Weimarn ratio

Question 5

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

Answer 5

False, low

Question 6

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

Answer 6

Colloidal suspension

Question 7

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

Answer 7

Crystalline suspension

Question 8

Occurs when smaller particles clump together to form larger particles

Answer 8

Coagulation

Question 9

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

Answer 9

Ostwald Ripening

Question 10

One form of contamination of gravimetric precipitates

Answer 10

Coprecipitation

Question 11

Which of the ff is not an example of coprecipitated impurities

Inclusion
Occlusion
Exclusion
Surface adsorption
Mixed crystal formation
Mechanical entrapment

Answer 11

Exclusion

Question 12

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

Answer 12

Surface adsorption, washing

Question 13

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

Answer 13

Occlusion, digestion

Question 14

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

Answer 14

Inclusion, reprecipitate

Question 15

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

Answer 15

Mixed crystal formation

Question 16

Occurs when crystal lie close together during growth

Answer 16

Mechanical entrapment

Question 17

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

Answer 17

Volatilization gravimetry

Question 18

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

Answer 18

Electrogravimetry

Question 19

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

Answer 19

Thermogravimetry

Question 20

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

Answer 20

Thermogravimetry

Question 21

Characteristics of a gravimetric precipitating agent

Answer 21

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

Question 22

Process of precipitation gravimetry

Answer 22

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

Question 23

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

Answer 23

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

Question 24

Mechanism of precipitate formation

Answer 24

1. Nucleation (particles diameter of 10^-7 to 10^-4 cm)
2. Particle growth (particles diameter of greater than 10^-4 cm)

Question 25

Recall the optimum conditions for precipitation that will keep the ratio low to promote particle growth instead of further nucleation

Answer 25

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

Question 26

Recall the optimum conditions for precipitation that will keep the ratio low to promote particle growth instead of further nucleation

Answer 26

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

Question 27

Colloids are best precipitated from hot, stirred solutions containing sufficient electrolytes to ensure coagulation

Answer 27

True

Question 28

Colloid layers

Primary adsorptive layer
Secondary layer (counter layer)

Answer 28

High concentration, +
Low concentration, -

Question 29

Precipitation occurs in solution rich in dissolved solids so the initial precipitate is often impure

Answer 29

True

Question 30

One of the most accurate and precise methods of macro quantitative analysis

Answer 30

Gravimetric analysis

Question 31

Gravimetry DOES NOT require a series of standards for calculation of an unknown since calculations are based only on atomic or molecular weights

Answer 31

TRUE