Reduction-Oxidation Titrimetry Flashcards
____ is the vertical axis in oxidation/reduction titration curves and is generally an electrode potential instead of a logarithmic function.
Redox Titration Curves
____ are readily obtained by taking advantage of the fact that the two reactant species have known conc. ratios at chemical equivalence.
Equivalence Point Potentials
Derivation of Redox Titration Curves (4)
- Initial Potential
- Potential After Initial Addition
- Equivalent-Point Potential
- Potential After the Excess Addition
_____ are substances that change color upon being oxidized or reduced.
General Redox Indicators
The color change caused by redox indicators is independent of the chemical nature of the analyte and titrant and depends instead upon the _____ that occur as the titration progresses.
changes in the electrode potential of the system
General Redox Indicators (3)
- Iron(II) Complexes of Orthophenanthrolines
- Diphenylamine and its Derivatives
- Iodine Solutions
_____, also known as phenanthroline, form stable complexes with iron(II) and certain other ions.
Iron(II) Complexes of Orthophenanthrolines
____ are widely used in oxidation/reduction reactions involving iodine as an oxidant or iodide ion as the reductant.
Iodine Solutions
___ is the best-known specific indicator which forms a dark blue complex with triiodide ion.
Starch Indicator
Why is it necessary to filter an analyte solution?
To remove granular or powdered forms of metal.
____ is a powerful oxidizing agent capable of converting manganese(II) quantitatively to permanganate ion.
Sodium Bismuthate (NaBiO3)
____ is a powerful oxidizing agent that converts Cr(III) to dichromate, Ce(III) to Ce(IV), and Mn(II) to permanganate in acidic solutions.
Ammonium Peroxydisulfate
____ is a convenient oxidizing agent either as a solid sodium salt or as a dilute solution of the acid.
Sodium Peroxide and Hydrogen Peroxide
Standard solutions of most reducing agents tend to react with _____. For this reason, reductants are seldom used for the direct titrations of oxidizing analytes; indirect methods are used.
atmospheric oxygen
The most common indirect methods are based upon: (2)
- Iron(II) Solutions
- Sodium Thiosulfate
____ are readily prepared from iron(II) ammonium sulfate (Mohr’s salt) or form closely related iron(II) ethylenediamine sulfate (Oesper’s salt).
Iron(II) Solutions
____ is a moderately strong reducing agent that has been widely used to determine oxidizing agents by an indirect procedure that involves iodine as an intermediate.
Sodium Thiosulfate
In an iodine test, a negative test (starch is absent) should display a ____ color. While in a positive test, the color ____ is displayed.
brown/yellow; blue/purple
Variables that influence the rate of thiosulfate reaction include: (5)
- pH
- presence of microorganisms
- concentration of the solution
- presence of copper (II)
- exposure to sunlight
_____ is an excellent primary standard for thiosulfate solutions.
Potassium Iodide
The choice among the two (Potassium Permanganate and Cerium(IV) depends upon: (5)
- the strength of the analyte as a reducing agent
- the rate of reaction between oxidant and analyte
- the stability of the standard oxidant solutions
- the cost
- the availability of an indicator
The intense ____ color of potassium permanganate solution is sufficient to serve as an indicator for most titrations. The permanganate ions react slowly with the large conc. of manganese(II) ions present at the endpoint.
purple
Solutions of Cerium(IV) are ____ but the color is not intense enough to act as an indicator in titrations. The most widely used indicator is the iron(II) complex of 1,10-phenanthroline or one of its derivatives.
yellow-orange
Permanganate solutions when prepared properly, are stable because ____. It is catalyzed by light, heat, acids, bases, manganese(II), and manganese dioxide. Standardized permanganate solutions should be stored in the dark.
the decomposition reaction is slow
