Volumetric analysis (titration)
titration: an analytical procedure that allows us to measure the volume of solution, which is
needed to react exactly with the another solution of unknown concentration
titrimetric reagent: a reactant of exactly konwn concentration
a reactant is placed in a burette
a reactant is added to other solution until equivalence point
equivalence point: endpoint of titration
- indicator: a substance that is generally added to the solution changes colour when reaction is
over
- measurement of physical properties of solution: pH
preparing of titr. reagent
solution: dissolving of exact amount of pure salt
preparing of approximate concentration of reactant and standardising this solution by standard
solution
titration curves: measurement of changes of physical properties during titration
- linear curves- changes of conductivity,..
- logarithmic curves- changes of pH, reduction potential
Titration types
acid-base reactions
H+ + OH-  H2O
acids: HCl, H2SO4, HNO3, HClO4
bases: NaOH, KOH, Ba(OH)2
indicators: methyl violet (yellow-violet), methyl orange (pink-yellow), phenolphthalein
(colourless-pink)
oxidation-reduction reactions (redox)
consist of two half-reaction
oxidation: Red  Ox + e
reduction: Ox + e  Red
most common oxidising agents:
MnO4in acid solution: MnO4- + 8H+ + 5e  Mn2+ + 4H2O
determination: Fe2+, H2O2, As3+, I, NO2Cr2O72Cr2O72- + 14H+ + 6e  2Cr3+ + 7H2O
determination of the same compounds as by titration with KMnO4
I2
I2 + 2e  2Idetermination: SO32-, S2O32-, Sn2+
most common reducing agent:
Na2S2O3,
2 S2O32- (thiosulfate ion)  S4O62- (tetrathionate ion) + 2edetermination of I2
precipitation reactions
are based on formation of a precipitate
most common reagent is AgNO3:
AgNO3 + NaCl  AgCl (insoluble salt) + NaNO3
determination: Cl-, Br-, I-, SCN-
complex ion reaction
leads to formation of stable complexes, that are soluble in water
M (central metal ion) + nL (ligands)  [MLn] (complex) the most stable metal
complexes create special (multivalent) ligands (have more donor atoms) as EDTA
titration with EDTA are used for determination of a lot of metal ions (Ca2+, Mg2+)
Reference:
1. http://www.tele.ed.nom.br/buret.html
2. General chemistry / Uno Kask, J. David Rawn ; with contributions from Ronald A.
DeLorenzo. - Dubuque, Iowa : WCB, cop. 1993 - xxiv, 1000 s. : il. ISBN 0697121445
[UK-LF3]
3. General chemistry : principles and structure / James E. Brady. - 5th ed.. - New York :
Wiley, cop. 1990 - xviii, 852, [67] s. : il. ISBN 0-471-62131-5 [UK-LF3]
1.