Gravimetric analysis

Question 1

quantative methods that are based on determining the mass of a pure compound to which the analyte is chemical related

Answer 1

gravimetric methods

Question 2

the analyte is separated from other constituents of a sample by converting it to a gas of known chemical composition. The mass of the gas then serves as a measure of the analyte concentration

Answer 2

volatilisation gravimetry

Question 3

the analyte is separated from a solution of the sample as a precipitate and is converted to a compound of known composition that can be weighed

Answer 3

precipitation gravimetry

Question 4

the analyte is separated by deposition on an electrode by an electrical current

Answer 4

electrogravimetry

Question 5

consists of solid particles with diameters that are less than 10^-4 cm

Answer 5

colloid

Question 6

in diffuse light, colloidal suspensions may be perfectly clear and appear to contain no solid. The presence of the second phase can be detected, however, by shining the beam of a flashlight into the solution. Because particles of colloidal dimensions** scatter visible radiation,** the path of the beam through the solution can be seen by the eye.

Answer 6

Tyndall effect

Question 7

process of particles clumping together when their oppositely charged particles aggregate together

Answer 7

coagulation

Question 8

process of converting precipitate into colloid by shaking it with a suitable electrolyte called peptizing agent

Answer 8

peptization

Opposite of coagulation

Question 9

solution that has less solute dissolved than its saturated concentration

Answer 9

unsaturated solution

Question 10

solute dissolves until it is unable to dissolve anymore

Answer 10

saturated solution

Question 11

unstable solution that contains a higher solute concentration than a saturated solution. An excess solute precipitates with time

Answer 11

supersaturated solution

Question 12

steps in precipitation gravimetry

Answer 12

1) preparation of the solution
2) precipitation
3) digestion
4) filtration
5) washing
6) drying or igniting
7) weighing
8) calculations

Question 13

the ideal precipitating reagent would react with the analyte to give a product that is

Answer 13

• easily filtered and washed free of contaminants
• of suffciently low solubility that no significant loss of the analyte occurs during filtration and washing
• unreact with constituents of the atmosphere
• of known chemical composition after it is dried or if necessary ignited

gravimetric precipitating agent

Question 14

should react specifically or at least selectively with the analyte

Answer 14

gravimetric precipitating agent

Question 15

react only with a single chemical species

Answer 15

specific reagents

Question 16

react with a limited number of species

Answer 16

selective reagents

Question 17

tiny particles are invisible to the naked eye and show no tendancy to settle from solution and are difficult to filter. The particles are suspended

Answer 17

colloidal suspension

Question 18

the temporary dispersion of particles larger than tenths of a millimeter. The particles tend to settle spontaneously and are easily filtered

Answer 18

crystalline suspension

Question 19

a few ions, atoms or molecules come together to form a stable solid

Answer 19

nucleation

If nucleation predominated a large number of small particles result

Question 20

ions/atoms/molecules are added to the nucleus to form larger particles

Answer 20

particle growth

If particle growth predominated, a smaller number of large particles result

Question 21

what particle size of a precipitate is influenced by:

Answer 21

• precipitate solubility
• temperature
• reactant concentrations
• rate at which precipitating agent is added

Question 22

particle size relative to a single property of the system

Answer 22

relative supersaturation

Question 23

relative superaturation

Answer 23

concentration of the solute at any instant- equilibrium solubility/ equilibrium solubility

relative supersaturation = Q - S/S

Question 24

The ____ the relative supersaturation value, the larger the particles

Answer 24

lower

Question 25

The lower the relative supersaturation value, the larger the particles