COMPLEXATION and PRECIPITATION TITRIMETRY

Question 1

Uses ___ for TITRATING CATIONS.

These reagents are ORGANIC COMPOUNDS that contain several ___ that form mutiple COVALENT BONDS with METAL IONS

Answer 1

Complex-forming reagents

electron-donor groups

Question 2

___ is a positively charged ion, i.e. one that would be attracted to the ___ in electrolysis.

Answer 2

cation

cathode

Question 3

Most METAL IONS react with ____ to form COORDINATION COMPOUNDS or ___.

Answer 3

Electron-pair donors

Coordination compounds/complexes

Question 4

The DONOR SPECIES or ____ must have at least ___ or ___ available for BOND FORMATION

Answer 4

Ligand

One pair
Unshared electrons

Question 5

The NUMBER OF COVALENT BONDS that a CATION(+) tends to FORM with ELECTRON DONORS is its ___

Answer 5

Coordination number

Question 6

Typical values for coordination number (3)

Answer 6

two

four

six

Question 7

TRUE or FALSE

Species formed as a result of coordination can only be electrically neutral

Answer 7

FALSE

They can be positive, neutral, or negative

Question 8

TRUE or FALSE

all nonmetal ions are found as COMPLEX IONS (a.k.a COORDINATION COMPLEXES)

Answer 8

FALSE

ALMOST ALL METAL IONS are found as COMPLEX IONS

Question 9

Parts of Complex ions / coordination complexes(3)

Answer 9

Ligand (outer)

Metal Ion (center) ex. CO3+

Counter ion, for charge balance (Cl-)3

Question 10

___ are TITRIMETRIC methods based on COMPLEX FORMATION

Based upon a particular class of COORDINATION COMPOUNDS called ____

Answer 10

Complexometric methods

Chelates

Question 11

Chelate is produced when a metal ion coordinates with ___ to form a ___

Answer 11

two or more DONOR GROUPS of a SINGLE LIGAND

FIVE- to SIX- membered HETEROCYCLIC RING

Question 12

Types of ligands based on donor groups: (3 main)

Answer 12

Unidentate = 1
Bidentate = 2
Tridentate = 3

Tetradentate, Pentadentate, Hexadentate

Question 13

What are the adventages of MULTIDENTATE over UNIDENTATE ligands? (2)

Answer 13

They generally REACT MORE COMPLETELY with CATIONS thus providing SHARPER END POINTS

MULTIDENTATE ORDINARILY REACT with METAL IONS in a SINGLE STEP PROCESS (UNIDENTATES take TWO or MORE TERMEDIATE SPECIES)

Question 14

Titrations with ___

TERTIARY AMINES (with N and lone pair) that contains ___ form STABLE CHELATES with many ___

Answer 14

Aminocarboxylic Acids

Carboxylic acid groups

metal ions

Question 15

MOST widely used COMPLEXOMETRIC TITRANT

has ___ POTENTIAL SITES for BONDING to a METAL ION; the ___ and __

It is a ___ ligand.

Answer 15

Ethylenediaminetetraacetic acid (EDTA)

SIX

FOUR CARBOXYL GROUPS

TWO AMINO GROUPS

HEXADENTATE LIGAND

Question 16

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(+)

Example, silver and aluminum complexes
Ag^+ + Y^4-

Al^3+ + Y^4-

Answer 16

1:1 RATIO

Ag^+ + Y^4- = AgY^3-

Al^3+ + Y^4- = AlY^-

Question 17

Many CATIONS form ___ when the pH is RAISED to the level REQUIRED FOR SUCCESSFUL TITRATION w/ EDTA

An ___ is NEEDED to keep the CATION in the solution

Answer 17

oxide precipitates (hydroxides, oxides, or oxyhydroxides)

Auxillary complexing agent

Question 18

Zinc (II) is usually titrated in a medium that has fairly fairly high concentrations of ___ and ___

Answer 18

Ammonia

Ammonium Chloride

Question 19

___ are usually ORGANIC dyes that form colored ___ with METAL IONS in a ___ range that is characteristic of a particular ___ and dye.

Answer 19

Indicators for EDTA titrations

chelates

pM

cation

Question 20

___ is typically a ___ indicator used in titration of several cCOMMON CATIONS but behaves as an ___ indicator. It forms ___ with more than TWO DOZEN metal ions. But only few are appropriate for END POINT DETECTION

Answer 20

Erichrome Black T

metal-ion

acid/bae

Red complexes

Question 21

MORDANT BLACK II components, color, and pH (4)

Answer 21

Erichrome Black T

Solochrome Black T

Blue

pH=10

Question 22

MUREXIDE vs MUREXIDE-CALCIUM COMPLEX color

Answer 22

Murexide Blue - Purple

Murexide-Calcium complex - Red

Question 23

____ is the total ___ and ___ concentration in a WATER SAMPLE and is EXPRESSED as the CONCENTRATION of ___.

Answer 23

Water Hardness

calcium
magnesium ion

Calcium carbonate

Question 24

Historically, WATER “HARDNESS was” defined in terms of the capacity of CATIONS in the water to REPLACE the ___ or ___ ions in SOAP

This forms BARELY SOLUBLE products that cause SCUM in the sink or bathtub

Answer 24

sodium

potassium

Question 25

____ are based on reactions that yield IONIC compounds of limited ____.

Answer 25

Precipitation titrations

solubility

Question 26

The most widely used PRECIPITATING REAGENT is ___

Titrations with this reagent is called ___.

Answer 26

Silver nitrate

Argentometric titrations

Question 27

SILVER NITRATE is used for the detrmination of (5)

Answer 27

halogens

halogen-like anions

mercaptans

fatty acids

divalent inorganic anions

Question 28

Most INDICATORS for ARGENTOMETRIC TITRATIONS respond to changes in the CONCENTRATIONS of ___.

Because of this, ___ for precipitation reactions usually consist of a plot of ___ versus ___ (usually ____)

Answer 28

silver ions

titration curves

pAg versus vol. of Silver reagent (usually AgNO3)

Question 29

Endpoints of argentometric titrations can be observed by ___ or ___

Answer 29

potentiometry (voltage)

amperometry (amperes)

Question 30

Endpoints of argentometric titrations chemical indicators (2)

Answer 30

Volhard Method

Mohr method

Question 31

In the VOLHARD method for finding argentometric end points, SILVER IONS are titrated with a standard solution of ___.

Answer 31

thiocyanate ion

Question 32

Indicator of VOLHARD is ___.

Solution turns ___ with the first slight excess of ___ due to the formation of ____.

Answer 32

Iron (III)

Red

Thiocyanate ion

Fe(SCN)2+

Question 33

In the MOHR method for finding argentometric end points, SILVER IONS are titrated with a standard solution of ___

Answer 33

Chromate

Question 34

Indicator of MOHR is ___.

Solution turns into a __ in the ___.

Answer 34

Sodium Chromate

brick-red silver chromate (Ag2CRO4) precipitate in the EQUIVALENCE-POINT region