Ch 12 Gravimetric Method of Analysis

Question 1

are quantitative methods that are based on determining the mass of a pure compound to which
the analyte is chemically related.

Answer 1

Gravimetric methods

Question 2

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 2

precipitation gravimetry

Question 3

the analyte is separated from other constituents of a sample by converting it to a gas of known chemical composition.

Answer 3

volatilization gravimetry

Question 4

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

Answer 4

electrogravimetry

Question 5

the mass of a reagent of known concentration required to
react completely with the analyte provides the information needed to determine the analyte
concentration.

Answer 5

gravimetric titrimetry,

Question 6

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

Answer 6

A colloid

Question 7

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

Answer 7

colloidal suspensions

Question 8

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

Answer 8

Tyndall effect

Question 9

is an unstable solution that contains a
higher solute concentration than a
saturated solution. As excess solute
precipitates with time, supersaturation
decreases to zero

Answer 9

A supersaturated solution

Question 10

The effect of relative supersaturation on particle size can be explained if we assume
that precipitates form in two ways:

Answer 10

nucleation and particle growth

Question 11

To increase the particle size
of a precipitate, _______ the
relative supersaturation during
precipitate formation

Answer 11

decreased

Question 12

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

Answer 12

Nucleation

Question 13

Individual colloidal particles are so small that they are not retained by ordinary filters. Moreover, the ____________ prevents their settling out of solution under the
influence of gravity. F

Answer 13

Brownian motion

Question 14

A type of precipitation process wherein , a large
number of very fine particles
is produced

Answer 14

Nucleation

Question 15

when a precipitate is formed at high
relative supersaturation, __________ is the major precipitation mechanism, and a large
number of small particles is formed

Answer 15

nucleation

Question 16

Low relative supersaturation
produces _______________

Answer 16

crystalline suspensions.

Question 17

What law describe colloids?

Answer 17

Brownian motions

Question 18

This prevents colloids from settling out of the solution under the
influence of gravity. Fortunately, however, we can coagulate, or agglomerate, this individual particles to give a filterable, amorphous mass that will settle
out of solution.

Answer 18

Brownian motion

Question 19

Coagulation can be hastened by

Answer 19

heating, by stirring, and by adding an electrolyte to the medium.

Question 20

Colloidal suspensions are stable because of

Answer 20

the repulsion force from the particles of the colloid that are either
positively or negatively charged

Question 21

the double layer that exerts an electrostatic repulsive force that prevents particles from colliding
and adhering

Answer 21

electric double layer

Question 22

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

Answer 22

Peptization

Question 23

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 23

Digestion

Question 24

is the solution from
which a precipitate was formed.

Answer 24

Mother liquor

Question 25

is a process in which normally soluble compounds are carried out of solution by a precipitate.

Answer 25

Coprecipitation

Question 26

four types of coprecipitation:

Answer 26

surface adsorption, mixed-crystal formation, occlusion, and mechanical entrapment

Question 27

From the four coprecipitation, which are product of equilibrium processes, and kinetics of crystal growth.

Answer 27

Surface adsorption and mixed-crystal formation are equilibrium processes, and occlusion and mechanical entrapment arise from the kinetics of crystal growth.

Question 28

is often the major source of contamination in coagulated colloids but of no significance in crystalline precipitates.

Answer 28

Surface adsorption

Question 29

The purity of many coagulated colloids is improved by .

Answer 29

digestion

Question 30

is defined as the surface area per unit mass of solid and usually has the units of square centimeters per gram.

Answer 30

Specific surface area

Question 31

For a given mass of solid, the specific surface area increases dramatically as particle size _______, and it becomes enormous for colloids

Answer 31

decreases

Question 32

A drastic but effective way to minimize the effects of adsorption

Answer 32

Reprecipitation

Question 33

is a type of coprecipitation in which a contaminant ion replaces an ion in the lattice of a crystal.

Answer 33

Mixed-crystal formation

Question 34

is a type of coprecipitation in which a compound is trapped within a pocket formed during rapid crystal growth.

Answer 34

Occlusion

Question 35

Mixed-crystal formation may occur in both

Answer 35

colloidal and crystalline precipitates

Question 36

occurs when crystals lie close together during growth. Several crystals grow together and in so doing trap a portion of the solution in a tiny pocket.

Answer 36

Mechanical entrapment

Question 37

occlusion and mechanical entrapment are confined to

Answer 37

crystalline precipitates.

Question 38

is a process in which a precipitate is formed by slow generation of a precipitating reagent homogeneously throughout a solution.

Answer 38

Homogeneous precipitation

Question 39

After precipitation, the precipitate is usually _____ to remove excess solvent

Answer 39

oven dry

Question 40

Some precipitates are also ignited to decompose the solid and form a compound of known composition. This new compound is often called the .

Answer 40

weighing form

Question 41

Organic reagents that yield sparingly soluble coordination compounds typically contain at least two functional groups. Each of these groups is capable of bonding with a cation by donating a pair of electrons. The functional groups are located in the molecule such that a five- or six-membered ring results from the reaction.

Answer 41

chelating agents

Question 42

Some organic reagent can precipitate slightly soluble nonionic products called

Answer 42

coordination compounds

Question 43

are cyclical metal-organic compounds in which the metal is a part of one or more five- or six-membered rings.

Answer 43

Chelates

Question 44

are relatively nonpolar and, as a consequence, have solubility that are low in water but high in organic liquids.

Answer 44

chelates

Question 45

Name some chelating or precipitating agent

Answer 45

8-Hydroxyquinoline (oxine) Dimethylglyoxime Sodium Tetraphenylborate

Question 46

is an organic precipitating agent that produce precipitate that are so bulky

Answer 46

Dimethylglyoxime

Question 47

is an important example of an organic precipitating reagent that forms salt-like precipitates.

Answer 47

Sodium tetraphenylborate

Question 48

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

Answer 48

water and carbon dioxide