Complexation and Precipitation Titrimetry

Question 1

_____ uses complex-forming reagents for titrating cations.

Answer 1

Complex-Formation Titrations

Question 2

____ are reagents that are organic compounds that have several electron-donor groups that form multiple covalent bonds with metal ions.

Answer 2

Complex-Forming Reagents

Question 3

Most metal ions react with _____ to form coordination compounds or complexes.

Answer 3

electron-pair donors

Question 4

The donor species or ligand must have ____ available for bond formation.

Answer 4

at least one pair of unshared electrons

Question 5

The number of covalent bonds a cation tends to form with electron donors is its ____ typical values for coordination numbers are _____.

Answer 5

coordination number; two, four, and six

Question 6

True or False
The species formed as a result of coordination can be electrically positive, neutral, or negative.

Answer 6

True

Question 7

____ are titrimetric methods based on complex formation. They are based on a particular class of coordination compounds called chelates.

Answer 7

Complexometric Methods

Question 8

___ are 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 8

Chelates

Question 9

Ligands can be:

Answer 9

Unidentate = 1 donor group
Bidentate = 2 donor groups
Tridentate = 3 donor groups
Tetradentate = 4 donor groups
Pentadentate = 5 donor groups
Hexadentate = 6 donor groups

….

Question 10

Advantages of multidentate over unidentate ligands. (2)

Answer 10

1. They generally react more completely with cations and provide sharper end points.
2. They ordinarily react with metal ions in a single-step process where a unidentate ligand usually involves two or more intermediate species.

Question 11

_____ is the most widely used complexometric titrant. It has six potential sites for bonding a metal ion; the four carboxyl groups and two amino groups. It has a hexadentate ligand.

Answer 11

Ethylenediaminetetraacetic Acid (EDTA)

Question 12

Solutions of EDTA are particularly valuable as titrants because the EDTA combines with metal ions in a ____ ratio regardless of the charge on the cation.

Answer 12

1:1

Question 13

Many cations form _____ when the pH is raised to the level required for their successful titration with EDTA.

Answer 13

hydrous oxide precipitates (hydroxides, oxides, or oxyhydroxides)

Question 14

An _____ is needed to keep the cation in solution.

Answer 14

auxiliary complexing agent

Question 15

____ are organic dyes that form colored chelates with metal ions in a pM range that is characteristic of a particular cation and dye.

Answer 15

Indicators for EDTA Titrations

Question 16

____ is typically a metal-ion indicator used in the titration of several common cations but behaves as an acid/base indicator. It forms red complexes with more than two dozen metal ions. But only a few are appropriate for endpoint detection.

Answer 16

Erichrome Black T (EBT)

Question 17

_____ is the total calcium and magnesium ion concentration in a water sample and is expressed as the concentration of calcium carbonate.

Answer 17

Water Hardness

Question 18

Historically, water “hardness” was defined in terms of the capacity of cations in the water _____.

Answer 18

to replace the sodium or potassium ions in soaps and form sparingly soluble products that cause “scum” in the sink or bathtub

Question 19

Precipitation titrations are based on reactions that _____.

Answer 19

yield ionic compounds of limited solubility

Question 20

Titrations with silver nitrate are sometimes called _____.

Answer 20

argentometric titrations

Question 21

Most indicators for argentometric titrations respond to changes in the _____.

Answer 21

concentrations of silver ions

Question 22

Endpoints can be observed by ____.

Answer 22

potentiometry/amperometry

Question 23

In this method, silver ions are titrated with a standard solution of thiocyanate ions. Iron(III) serves as the indicator. The solution turns red with the first slight excess of thiocyanate ion due to the formation of Fe(SCN)2+.

Answer 23

Volhard Method

Question 24

In this method, 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 24

Mohr Method