3rd Exam Complexation and Precipitation Titrimetry

Question 1

uses complex-forming reagents for titrating cations.

Answer 1

Complex-Formation Titrations

Question 2

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

Answer 2

complex-forming reagents

Question 3

Most metal ions react with electron-pair donors to form _________ or _________.

Answer 3

coordination compounds or complexes

Question 4

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

Answer 4

at least one pair or unshared electrons

Question 5

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

Answer 5

coordination number

Question 6

typical values for coordination number are

Answer 6

two, four, and six.

Question 7

True or False

The species formed as a result of coordination can be electrically positive.

Answer 7

False

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

Question 8

True or False

Almost all metal ions are found as complex ions or coordination complexes

Answer 8

True

Question 9

_______ are titrimetric methods based on complex formation which is based upon a particular class of coordination compounds called _____.

Answer 9

Complexometric methods;

chelates

Question 10

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 10

Chelate

Question 11

Ligands can be: (6)

Answer 11

◦ Unidentate = 1 donor group
◦ Bidentate = 2 donor groups
◦ Tridentate, tetradentate, pentadentate, hexadentate

Question 12

Advantages of multidentate over unidentate ligands: (2)

Answer 12

◦ react more completely with cations and provide sharper end points
◦ react with metal ions in a single step process where as unidentate ligands usually involves two or more intermediate species.

Question 13

Tertiary amines that contains carboxylic acid groups which form stable chelates with many metal ions.

Answer 13

Aminocarboxylic Acids

Question 14

= most widely used complexometric titrant
= has six potential sites for bonding a metal ion
= a hexadentate ligand.

Answer 14

Ethylenediaminetetraacetic acid (EDTA)

Question 15

A titration curve for the reaction of a cation Mn+ with EDTA consist of a plot of _____ versus __________

Answer 15

pM versus reagent volume

Question 16

coordination compounds part (3)

Answer 16

• metal ion
• ligand
• counter ion (for charge balance)

Question 17

6 potential sites of EDTA

Answer 17

four carboxyl groups and two amino groups

Question 18

Cu-EDTA complex charge

Answer 18

2-

Question 19

the EDTa combines sith metal ions in a ______ ratio regardless of the charge of cation

Answer 19

1:1 ratio

Question 20

is also used as food preservative

Answer 20

EDTA

Question 21

many cations form _________ when the pH is raised to the level required for their successful titration with EDTA

Answer 21

hydrous oxide precipitate

Question 22

hydrous oxide precipitate (3)

Answer 22

hydroxides, oxides, or oxyhydroxides

Question 23

is needed to keep thr cation in solution

Answer 23

auxiliary complexing agent

Question 24

an example of auxiliary agent when titrating zinc (II) with EDTA

Answer 24

zinc(Ii) is usually titrated in a medium that has fairly high concentrations of ammonia and ammonium chloride

Question 25

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

Answer 25

Indicators for EDTA Titrations

Question 26

example of Indicator for EDTA

Answer 26

Erichrome Black T

Question 27

typically a metal-ion indicator used in titration of several common cations but behaves as an acid /base indicator.

Answer 27

Erichrome Black T

Question 28

Erichrome Black T forms _______ complexes with kore than two dozen metal ions. But only a few are appropriate for end point detection.

Answer 28

red complexes

Question 29

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

Answer 29

Water hardness

Question 30

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 30

water “hardness”

Question 31

are based on reactions that yield ionic compounds of limited solubility.

Answer 31

precipitation titrations

Question 32

• most widely use and important precipitating reagent
• is used for the detrmination of halogens, the halogenlike anions, mercaptans, fatty acids, and several divalent inorganic anions.

Answer 32

silver nitrate

Question 33

titrations with silver nitrate are sometimes

Answer 33

argentometric titrations

Question 34

Most indicators for argentometric titrations respond to changes in the ______________

Answer 34

concentrations of silver ions

Question 35

titration curves for precipitation reactions usually consist of a plot of _________ versus ___________

Answer 35

plot of pAg versus volume of the silver reagent (usually AgNO3).

Question 36

Endpoints pf srgentometric titrations can be observed by ?

Answer 36

potentiometry/amperometry

Question 37

Chemical indicators (2)

Answer 37

Volhard Method
Mohr Method

Question 38

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

The solution turns _______ with the first slight excess of thiocyanate ion due to the formation of Fe(SCN)2+.

Answer 38

Volhard Method; Red

Question 39

Volhard Method indicator

Answer 39

Iron (III)

Question 40

sodium chromate serves as the indicator for the argentometric titration of chloride, bromide, and cyanide ions.

Silver ions react with chromate to form the ____________ precipitate in the equivalence-point region.

Answer 40

Mohr method; brick-red silver chromate (Ag2CrO4)