REDUCTION-OXIDATION TITRIMETRY Flashcards
___ Is based on an OXIDATION-REDUCTION reaction between the ANALYTE and TITRANT.
Frequently, either the reactants or titrant have a color INTENSE enough that a ___ is not needed.
Redox titration
additional indicator
OXIDIZING AGENT =
REDUCING AGENT =
SUBSTANCE REDUCED
SUBSTANCE OXIDIZED
Commonly used to determine the endpoint of a redox equation (2)
Potentiometer
Redox Indicator
Oxidation : ____ : ____
Reduction : ____ : ____
Oxidation : Lose e- : Gain charge (OLEG)
Reduction : Gain e- : Lose charge (RGEL)
POLYATOMIC IONS
Even Odd
Even Even
Odd Odd
If has H,
POLYATOMIC IONS
Even Odd -1
Even Even -2
Odd Odd +1
If has H, +1
TRUEor FALSE
The equivalence point can be obtained by the stoichiometric reaction in Redox Equations
FALSE
Obtained through the fact that reactant species have conc. ratios at chemical equivalence
Substances that change color upon being oxidized or reduced.
The color change is INDEPENDENT of the CHEMICAL nature of the ANALYTE and TITRANT
It DEPENDS on the CHANGES in the ___ of the system that occur as the titration progresses
General Redox Indicator
Electrode potential
Types of General Redox Indicator (3)
Iron (II) Complexes of orthophenathrolines
Diphenylamine
Iodine solutions
It is the best known SPECIFIC indicator which forms a ____ complex with Triiodide ion
STARCH INDICATOR
powerful oxidizing agent capable of converting
manganese(II) quantitatively to permanganate ion.
oxidations are performed by suspending the (answer) in the analyte solution and boiling for a brief period.
Sodium Bismuthate (NaBiO3)
powerful oxidizing agent that converts Cr(III) to dichromate, Ce(III) to Ce(IV), and Mn(II) to permanganate in acidic solutions.
oxidations are catalyzed by traces of silver ion
Ammonium Peroxydisulfate
E°=2.01 V
a convenient oxidizing agent either as a solid sodium salt or as a dilute solution of the acid.
Sodium peroxide and Hydrogen Peroxide
E°=1.78 V
Auxillary agents are for what?
Auxillary oxidizing agents convert all analytes into their oxiddized states
Fe to all Fe3+
Auxillary reducing agents convert all analytes into their reduced states
Fe to all Fe2+
reductants are seldom used for the direct titrations of oxidizing analytes; indirect methods are used.
Why?
Standard solutions tend to interact w/ atmospheric oxygen
Common indirect methods of reductants (2)
Iron (II) solution
Sodium Thiosulfate
moderately strong reducing agent that has been widely used to determine oxidizing agents by indirect procedure that involves iodine as an intermediate.
END POINT IS DISAPPEARANCE OF IODINE COLOR
Sodium Thiosulfate
IODINE titrations are performed with a suspension of STARCH INDICATOR
Negative test (starch absent) -
Positive Test (starch present) -
Negative test (starch absent) -Brown/Yellow
Positive Test (starch present) - Blue/Purple
Variables that influence the rate of thiosulfate reaction include
- pH
- presence of microorganisms
- concentration of the solution
- presence of copper (II)
- exposure to sunlight
Standardization of Thiosulfate solutions
1 mol IO3- = ____ = ____
1 mol IO3- = 3 mol I2 = 6 mol S2O3 2-
The strong oxidants (2)
Potassium Permanganate
Cerium (IV)
Choice between common oxidants used as standard solutions depends on (5)
- the strength of the analyte as a reducing agent,
- the rate of reaction between oxidant and analye,
- the stability of the standard oxidant solutions,
- the cost
- the availability of indicator
Primary Stnadard
used to standardize permanganate and cerium(IV) solutions. In acidic solution, the oxalate is converted to
the undissociated acid.
. Sodium Oxalate
dichromate ion is reduced to green chromium(III) ion.
indefinitely stable , can be boiled w/o decomposition and do not react with HCl.
primary standard reagent is available commercially and at modest cost
BUT low electrode potential and slow
Potassium Dichromate
Indicator for dichromate solution oxidant titrations
diphenylamine sulfunic is an excellent indicator for this titration. The oxidized form of the indicator is violet, and the reduced form is essentially colorless
Green to violet
weak oxidizing agents that are used for the determination of strong reductants.
Selective but lacks stability
Iodine
used for the determination of organic compounds that contain oleffinic and certain type of aromatic functional groups
reacts selectively with organic compounds having hydroxyl, carbonyl, or amine groups on adjacent carbon atoms.
widely employed for the determination of water in a variety of organic or inorganic samples.
Potassium bromate
Periodic acid
Karl Fischer reagent
