Complexation Equilibria And Complexometric Methods Flashcards
Metal ligand titrations started with the determination of CN-and Cl- using Ag+ and Hg+ as titrants, respectively. Both are developed by
Justus von Liebig
First use of ____ as titrant occured when Schwarzenbach introduced ______ as indicators for detecting the endpoint of a complexometric titration.
EDTA, metallochromic dyes
During complex formation, metal ions (M) acts as lewis base, donating electron pairs to ligands (L), which are lewis acid.
False
Complexation reactions occur in a stepwise manner, each having an equilibrium constant called _____,
Formation constant (kf)
Kf is a measure of _______ of the L for the M relative to similar complexes formed with other metals.
Selectivity
At equilibrium, metal ion M is present in both complex ML and in free metal form
True
EDTA is
Ethylenediaminetetraacetic acid
Refers to the ability of multidentate ligands to form more stable complexes.
Chelate effect
Which of the ff. are synthetic chelating agents?
I. nitriloacetic acid (NTA)
II. trans-1,2-diaminocyclohexanetetraacetic acid (DCTA)
III. diethylenetriaminepentaacetic acid (DTPA)
IV. ethylenediaminetetraacetic acid (EDTA)
I, II, III, IV
Most widely used chelator forming strong 1:1 complexes with many metal ions.
EDTA
EDTA has 4 binding sites: 2 carboxylate groups, 2 amino groups. Thus, the resulting complex is very stable.
False. 6 binding sites: 4 carboxylate, 2 amino groups
The fully protonated form of EDTA _____ predominates at very ____ pH. Fully deprotonated form _____ predominates at very _____ pH.
H6Y2+, low
Y4-, high
Neutral EDTA is
H4Y
Commonly used form of EDTA
disodium salt (Na2H2Y•2H2O)
Form of EDTA that binds to metal ions
Fully deprotonated form (Y4-)
Metal-EDTA complexes (MY4-) are unstable at extreme pH levels, thus EDTA titrations are usually carried out at _____ pH usually at _____.
Buffered pH at 10-12
Second ligand called ______ is used to prevent the metal ion from precipitating. Forms weak complex with metal ion, and displaced by EDTA during titration
auxiliary complexing agent
Which of the following are examples of auxiliary complexing agents
I. Ammonia
II. Citrate
III. Oxalate
IV. Tartrate or triethanolamine
I, II, IV
Indicators used in complexation. These are organic dyes that form stable complexes with metal ions.
Metallochromic indicators
True or false. Most metallochromic indicators are weak acids or bases thus, formation if metal-indicator complex (MIn^n-3) depends on pH.
True
Common metallochromic indicators
EBT and Calmagite
Commonly used in the determination of hardness in water
EDTA titrations
Refers to the total concentration of polyvalent ions, mainly Ca2+ and Mg2+ in water. Commonly expressed in ppm CaCO3
Hardness
During titration, _____ (M-indicator compex reacts with EDTA forming a more stable M-EDTA complex) occurs causing a change in color (freeing the ____).
Displacement, indicator
This method of cyanide determination is the widely used complexometric titration using a monodentate ligand (CN-)
Liebig methods
This method of cyanide determination is the widely used complexometric titration using s monodentate ligand (CN-)
Liebig methods
During titration, the ratio of anyte (KCN) to titrant (AgNO3) is
2:1
In Liebig method, _____ is added to a solution of alkali cyanide until the formation of the complex, _______, is complete.
Further addition of titrant results in the formation of insoluble ______.
To obtain sharper endpoint, ______ is added prior to titration.
As soon as all the cyanide has reacted, the first excess of silver nitrate reacts with iodide to cause a permanent turbidity due to formation of ____.
Silver nitrate (AgNO3)
Dicyanoargentate (KAg(CN)2)
Silver cyanide ( AgCN)
Potassium iodide (KI)
Silver iodide (AgI)
