LEC Lesson 12

Question 1

are quantitative methods
that are based on determining the mass

Answer 1

Gravimetric methods

Question 2

Gravimetric method are based on mass measurements with an

Answer 2

Analytical balance

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 from other constituents of a sample
by converting it to a gas of known chemical
composition

Answer 4

volatilization gravimetry

Question 5

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

Answer 5

electrogravimetry

Question 6

react only with a single chemical
species

Answer 6

Specific reagents

Question 7

which are more common, react with
a limited number of specie

Answer 7

Selective reagents

Question 8

A gravimetric precipitating agent should react specifically or at
least selectively with the analyte and give a product that is:

Answer 8

1. Easily filtered
2. Has low solubility
3. Unreactive with constituents of the atmosphere
4. of known chemical composition after it is dried or, if necessary, ignited

Question 9

are generally
desirable for gravimetric work because these particles
are usually purer than fine particles, easy to filter, and
easy to wash free of impurities

Answer 9

Precipitates consisting of large particles

Question 10

A colloid consists of solid particles that ranges from?

Answer 10

10-7 to 10-4 cm

Question 11

show no tendency to settle
from solution and are difficult to filter

Answer 11

Colloidal particles

Question 12

Because particles of colloidal dimensions
scatter visible radiation, the path of the beam through the solution can be seen by the eye. This phenomenon is called the?

Answer 12

Tyndall effect

Question 13

The temporary dispersion of particles with
dimensions on the order of tenths of a millimeter or greater in the liquid phase is called a

Answer 13

crystalline suspension

Question 14

The particles of a crystalline suspension tend to?

Answer 14

settle spontaneously and are easily filtered

Question 15

The particle size of a precipitate is influenced by

Answer 15

1. Solubility
2. Temperature
3. Concentration
4. rate at which reactants are mixe

Question 16

The net effect of these variables can be accounted for
by assuming that the particle size is related to a single
property of the system called

Answer 16

relative supersaturation

Question 17

is an unstable solution that
contains a higher solute concentration than a saturated
solution

Answer 17

supersaturated solution

Question 18

is a process in which a minimum number of
atoms, ions, or molecules join together to give a stable
solid

Answer 18

Nucleation

Question 19

nucleation is the major
precipitation mechanism.

Answer 19

high relative
supersaturation

Question 20

the rate of particle growth tends to predominate, and deposition of solid on existing particles occurs

Answer 20

low relative supersaturations

Question 21

prevents colloid particles to settle
out of solution

Answer 21

Brownian motion

Question 22

Colloidal Precipitates have to be? In order to give a filterable, amorphous
mass that will settle out of solution.

Answer 22

Coagulated

Question 23

Coagulation can be hastened by

Answer 23

1. Heating
2. Stirring
3. adding an electrolyte to the medium

Question 24

a process in which a substance (gas,
liquid, or solid) is held on the surface of a solid

Answer 24

Adsorption

Question 25

the process by which a coagulated colloid reverts to its original dispersed state

Answer 25

Peptization

Question 26

is a process in which a precipitate is heated in the solution from which it was formed (the mother liquor) and allowed to stand in contact with the solution

Answer 26

Digestion

Question 27

is the solution from which a precipitate was formed

Answer 27

Mother liquor

Question 28

are generally more easily filtered and purified than are coagulated colloids

Answer 28

Crystalline precipitates

Question 29

improves the purity and filterability of both colloidal and crystalline precipitates

Answer 29

Digestion

Question 30

A gravimetric precipitate is heated until its mass becomes constant. This new compound is called the

Answer 30

weighing form

Question 31

Graphs show mass loss as a function of temperature for three analytical precipitates

Answer 31

silver chloride, barium sulfate, and aluminum oxide

Question 32

Recording thermal decomposition curves is called

Answer 32

thermogravimetric analysis

Question 33

Gravimetric methods do not require a calibration or standardization step because?

Answer 33

results are calculated directly from the experimental data and atomic masses

Question 34

forms slightly soluble nonionic products

Answer 34

coordination compounds

Question 35

forms products in which the bonding between the inorganic species and the reagent is largely

Answer 35

ionic

Question 36

is capable of bonding with a cation by donating a pair of electrons, yield sparingly soluble coordination compounds typically contain at least two functional groups. Reagents that form compounds of this type are called

Answer 36

chelating agents

Question 37

are relatively nonpolar and have solubilities that are low in water but high in organic liquids

Answer 37

Metal chelates

Question 38

The two most common gravimetric methods based on volatilization are those for determining

Answer 38

water and carbon dioxide

Question 39

water vapor is collected on any of several solid desiccants, and its mass is determined from the mass gain of the desiccant

Answer 39

direct determination

Question 40

the amount of water is determined by the loss of mass of the sample during heating.

Answer 40

indirect method