REDUCTION-OXIDATION TITRIMETRY

Question 1

___ 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.

Answer 1

Redox titration

additional indicator

Question 2

OXIDIZING AGENT =

REDUCING AGENT =

Answer 2

SUBSTANCE REDUCED

SUBSTANCE OXIDIZED

Question 3

Commonly used to determine the endpoint of a redox equation (2)

Answer 3

Potentiometer

Redox Indicator

Question 4

Oxidation : ____ : ____
Reduction : ____ : ____

Answer 4

Oxidation : Lose e- : Gain charge (OLEG)

Reduction : Gain e- : Lose charge (RGEL)

Question 5

POLYATOMIC IONS

Even Odd

Even Even

Odd Odd

If has H,

Answer 5

POLYATOMIC IONS

Even Odd -1

Even Even -2

Odd Odd +1

If has H, +1

Question 6

TRUEor FALSE

The equivalence point can be obtained by the stoichiometric reaction in Redox Equations

Answer 6

FALSE

Obtained through the fact that reactant species have conc. ratios at chemical equivalence

Question 7

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

Answer 7

General Redox Indicator

Electrode potential

Question 8

Types of General Redox Indicator (3)

Answer 8

Iron (II) Complexes of orthophenathrolines

Diphenylamine

Iodine solutions

Question 9

It is the best known SPECIFIC indicator which forms a ____ complex with Triiodide ion

Answer 9

STARCH INDICATOR

Question 10

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.

Answer 10

Sodium Bismuthate (NaBiO3)

Question 11

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

Answer 11

Ammonium Peroxydisulfate

E°=2.01 V

Question 12

a convenient oxidizing agent either as a solid sodium salt or as a dilute solution of the acid.

Answer 12

Sodium peroxide and Hydrogen Peroxide

E°=1.78 V

Question 13

Auxillary agents are for what?

Answer 13

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+

Question 14

reductants are seldom used for the direct titrations of oxidizing analytes; indirect methods are used.

Why?

Answer 14

Standard solutions tend to interact w/ atmospheric oxygen

Question 15

Common indirect methods of reductants (2)

Answer 15

Iron (II) solution

Sodium Thiosulfate

Question 16

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

Answer 16

Sodium Thiosulfate

Question 17

IODINE titrations are performed with a suspension of STARCH INDICATOR

Negative test (starch absent) -

Positive Test (starch present) -

Answer 17

Negative test (starch absent) -Brown/Yellow

Positive Test (starch present) - Blue/Purple

Question 18

Variables that influence the rate of thiosulfate reaction include

Answer 18

1. pH
2. presence of microorganisms
3. concentration of the solution
4. presence of copper (II)
5. exposure to sunlight

Question 19

Standardization of Thiosulfate solutions

1 mol IO3- = ____ = ____

Answer 19

1 mol IO3- = 3 mol I2 = 6 mol S2O3 2-

Question 20

The strong oxidants (2)

Answer 20

Potassium Permanganate

Cerium (IV)

Question 21

Choice between common oxidants used as standard solutions depends on (5)

Answer 21

• 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

Question 22

Primary Stnadard

used to standardize permanganate and cerium(IV) solutions. In acidic solution, the oxalate is converted to
the undissociated acid.

Answer 22

. Sodium Oxalate

Question 23

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

Answer 23

Potassium Dichromate

Question 24

Indicator for dichromate solution oxidant titrations

Answer 24

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

Question 25

weak oxidizing agents that are used for the determination of strong reductants.

Selective but lacks stability

Answer 25

Iodine

Question 26

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.

Answer 26

Potassium bromate

Periodic acid

Karl Fischer reagent