Chapter 15: Complexation and Precipitation Reactions and Titrations

Question 1

The number of covalent bonds that a cation tends to form with electron donors
is its

Answer 1

coordination number

Question 2

Titrations based on complex formation, sometimes called

Answer 2

complexometric titrations

Question 3

is produced when a metal ion
coordinates with two or more donor groups of a single ligand to form a five- or
six-membered heterocyclic ring.

Answer 3

chelate

Question 4

Another important type of complex is formed between metal ions and cyclic
organic compounds, known as macrocycles. These molecules contain nine or more
atoms in the cycle and include at least three heteroatoms, usually oxygen, nitrogen,
or sulfur.

Answer 4

macrocycles (e.g. crown ethers)

Question 5

form three dimensional cavities that can just accommodate appropriately sized metal ions

Answer 5

macrocyclic compounds

Question 6

are based on reactions that yield ionic compounds of limited solubility

Answer 6

precipitation titrations

Question 7

Titrations with silver nitrate are sometimes called

Answer 7

argentometric titrations

Question 8

end points used in argentometric titrations

Answer 8

chemical
potentiometric
amperometric

Question 9

the potential difference between a silver electrode and a reference electrode is measured as a function of titrant volume

Answer 9

potentiometric

Question 10

the current generated between a pair of silver electrodes is measured and plotted as a function
of titrant volume

Answer 10

amperometric

Question 11

produce a color change or occasionally the appearance or disappearance of turbidity in the solution being titrated.

Answer 11

chemical indicators

Question 12

this method, silver ions are titrated with a standard solution of thiocyanate ion:

Answer 12

volhard method

Question 13

sodium chromate serves as the indicator for the argentometric titration of chloride, bromide, and cyanide ions. Silver ions react with chromate to form the brick-red silver chromate (Ag2CrO4) precipitate in the equivalence-point region.

Answer 13

Mohr method

Question 14

uses an adsorption indicator, an organic compound that adsorbs onto or desorbs from the surface of the solid in a precipitation titration. Ideally, the adsorption or desorption occurs near the equivalence point and results not only in a
color change but also in the transfer of color from the solution to the solid or vice versa.

Answer 14

Fajans method

Question 15

organic complexing agents extracts

Answer 15

8-hydroxyquinoline
diphenylthiocarbazone
acetylacetone
ammonium pyrrolidine dithiocarbamate
thenoyltrifluoroacetone
dibenzo-18-crown-6

Question 16

Another important application of organic complexing agents is in forming stable
complexes that bind a metal and prevent it from interfering in a determination, which is also called as

Answer 16

masking agent

Question 17

is the most widely used complexometric
titrant.

Answer 17

EDTA
ethylenediamminetetraacetic acid

Question 18

When it is dissolved in water, EDTA behaves like an amino acid, such as

Answer 18

glycine

Question 19

is the second most common
amino-polycarboxylic acid used
for titrations. It is a tetradentate
chelating agent and has the
structure

Answer 19

nitrilotriacetic acid

Question 20

TRUE or FALSE
Solutions of EDTA are particularly valuable as titrants because the EDTA combines
with metal ions in a 1:1 ratio regardless of the charge on the cation.

Answer 20

TRUE

Question 21

TRUE or FALSE
EDTA is a remarkable reagent not only because it forms chelates with nearly all cations but also because most of these chelates are sufficiently stable for titrations and themselves colorless

Answer 21

TRUE

Question 22

TRUE or FALSE
The ability of EDTA to form complexes with metals is responsible for its widespread use as a preservative in foods and in biological samples

Answer 22

TRUE

Question 23

TRUE or FALSE
EDTA is an excellent preservative for foods
and is a common ingredient of such commercial food products
as mayonnaise, salad dressings, and oils

Answer 23

TRUE

Question 24

EDTA and other similar chelating agents are often called _______ because of their ability to remove or inactivate metal ions

Answer 24

sequestering agents

Question 25

are useful for the determination of cations that form stable EDTA complexes and for which a satisfactory indicator is not available

Answer 25

back titration

Question 26

is also useful for analyzing samples that contain anions that could form precipitates with the analyte under the analytical conditions

Answer 26

back titration

Question 27

an unmeasured excess of a solution containing the magnesium or zinc complex of EDTA is introduced into the analyte solution

Answer 27

displacement titrations

Question 28

is the most widely used complexometric
titrant.

Answer 28

EDTA

Question 29

is a typical metal-ion indicator that is used in the titration of several common cations. generally red in color of its metal complexes

Answer 29

Eriochrome Black T

Question 30

forms red complexes with more than two dozen metal ions, but the formation constants of only a few are appropriate for end-point detection

Answer 30

Eriochrome Black T

Question 31

contains calcium, magnesium, and heavy metal
ions that form precipitates with soap (but not detergents).

Answer 31

hard water

Question 32

was defined in terms of the capacity of cations in the water to replace the sodium or potassium ions in soaps and form sparingly soluble products that cause “scum” in the sink or bathtub

Answer 32

hard water

Question 33

forms the least stable EDTA complex of
all of the common multivalent cations in typical water samples is not titrated until
enough reagent has been added to complex all of the other cations in the sample

Answer 33

magnesium

Question 34

TRUE or FALSE
Water hardness is usually determined by an EDTA titration after the sample has
been buffered to pH 10

Answer 34

TRUE

Question 35

TRUE or FALSE
The formation of soluble complexes can be used to control the concentration of free
metal ions in solution and thus control their reactivity

Answer 35

TRUE

Question 36

One of the most common side reactions is that of a ligand that can protonate, that is, the ligand is a

Answer 36

weak acid or the conjugate base of a weak acid

Question 37

a metal ion reacts with a suitable ligand to form a complex, and the equivalence point is determined by an indicator or an appropriate instrumental method. The formation of soluble inorganic complexes is not widely used for titrations, but the formation of precipitates, particularly with silver nitrate as the titrant, is the basis for many important determinations

Answer 37

complexometric titrations

Question 38

Complexometric titration curves are usually a plot of

Answer 38

pM=-log[M] as a function of the volume of titrant added