COMPLEXATION and PRECIPITATION TITRIMETRY Flashcards

1
Q

Uses ___ for TITRATING CATIONS.

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

A

Complex-forming reagents

electron-donor groups

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2
Q

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

A

cation

cathode

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3
Q

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

A

Electron-pair donors

Coordination compounds/complexes

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4
Q

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

A

Ligand

One pair
Unshared electrons

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5
Q

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

A

Coordination number

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6
Q

Typical values for coordination number (3)

A

two

four

six

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7
Q

TRUE or FALSE

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

A

FALSE

They can be positive, neutral, or negative

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8
Q

TRUE or FALSE

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

A

FALSE

ALMOST ALL METAL IONS are found as COMPLEX IONS

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9
Q

Parts of Complex ions / coordination complexes(3)

A

Ligand (outer)

Metal Ion (center) ex. CO3+

Counter ion, for charge balance (Cl-)3

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10
Q

___ are TITRIMETRIC methods based on COMPLEX FORMATION

Based upon a particular class of COORDINATION COMPOUNDS called ____

A

Complexometric methods

Chelates

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11
Q

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

A

two or more DONOR GROUPS of a SINGLE LIGAND

FIVE- to SIX- membered HETEROCYCLIC RING

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12
Q

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

A

Unidentate = 1
Bidentate = 2
Tridentate = 3

Tetradentate, Pentadentate, Hexadentate

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13
Q

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

A

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)

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14
Q

Titrations with ___

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

A

Aminocarboxylic Acids

Carboxylic acid groups

metal ions

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15
Q

MOST widely used COMPLEXOMETRIC TITRANT

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

It is a ___ ligand.

A

Ethylenediaminetetraacetic acid (EDTA)

SIX

FOUR CARBOXYL GROUPS

TWO AMINO GROUPS

HEXADENTATE LIGAND

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16
Q

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-

A

1:1 RATIO

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

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

17
Q

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

A

oxide precipitates (hydroxides, oxides, or oxyhydroxides)

Auxillary complexing agent

18
Q

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

A

Ammonia

Ammonium Chloride

19
Q

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

A

Indicators for EDTA titrations

chelates

pM

cation

20
Q

___ 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

A

Erichrome Black T

metal-ion

acid/bae

Red complexes

21
Q

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

A

Erichrome Black T

Solochrome Black T

Blue

pH=10

22
Q

MUREXIDE vs MUREXIDE-CALCIUM COMPLEX color

A

Murexide Blue - Purple

Murexide-Calcium complex - Red

23
Q

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

A

Water Hardness

calcium
magnesium ion

Calcium carbonate

24
Q

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

A

sodium

potassium

25
____ are based on reactions that yield IONIC compounds of limited ____.
Precipitation titrations solubility
26
The most widely used PRECIPITATING REAGENT is ___ Titrations with this reagent is called ___.
Silver nitrate Argentometric titrations
27
SILVER NITRATE is used for the detrmination of (5)
halogens halogen-like anions mercaptans fatty acids divalent inorganic anions
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 ____)
silver ions titration curves pAg versus vol. of Silver reagent (usually AgNO3)
29
Endpoints of argentometric titrations can be observed by ___ or ___
potentiometry (voltage) amperometry (amperes)
30
Endpoints of argentometric titrations chemical indicators (2)
Volhard Method Mohr method
31
In the VOLHARD method for finding argentometric end points, SILVER IONS are titrated with a standard solution of ___.
thiocyanate ion
32
Indicator of VOLHARD is ___. Solution turns ___ with the first slight excess of ___ due to the formation of ____.
Iron (III) Red Thiocyanate ion Fe(SCN)2+
33
In the MOHR method for finding argentometric end points, SILVER IONS are titrated with a standard solution of ___
Chromate
34
Indicator of MOHR is ___. Solution turns into a __ in the ___.
Sodium Chromate brick-red silver chromate (Ag2CRO4) precipitate in the EQUIVALENCE-POINT region