Complexation Equilibria And Complexometric Methods

Question 1

Metal ligand titrations started with the determination of CN-and Cl- using Ag+ and Hg+ as titrants, respectively. Both are developed by

Answer 1

Justus von Liebig

Question 2

First use of ____ as titrant occured when Schwarzenbach introduced ______ as indicators for detecting the endpoint of a complexometric titration.

Answer 2

EDTA, metallochromic dyes

Question 3

During complex formation, metal ions (M) acts as lewis base, donating electron pairs to ligands (L), which are lewis acid.

Answer 3

False

Question 4

Complexation reactions occur in a stepwise manner, each having an equilibrium constant called _____,

Answer 4

Formation constant (kf)

Question 5

Kf is a measure of _______ of the L for the M relative to similar complexes formed with other metals.

Answer 5

Selectivity

Question 6

At equilibrium, metal ion M is present in both complex ML and in free metal form

Answer 6

True

Question 7

EDTA is

Answer 7

Ethylenediaminetetraacetic acid

Question 8

Refers to the ability of multidentate ligands to form more stable complexes.

Answer 8

Chelate effect

Question 9

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)

Answer 9

I, II, III, IV

Question 10

Most widely used chelator forming strong 1:1 complexes with many metal ions.

Answer 10

EDTA

Question 11

EDTA has 4 binding sites: 2 carboxylate groups, 2 amino groups. Thus, the resulting complex is very stable.

Answer 11

False. 6 binding sites: 4 carboxylate, 2 amino groups

Question 12

The fully protonated form of EDTA _____ predominates at very ____ pH. Fully deprotonated form _____ predominates at very _____ pH.

Answer 12

H6Y2+, low
Y4-, high

Question 13

Neutral EDTA is

Answer 13

H4Y

Question 14

Commonly used form of EDTA

Answer 14

disodium salt (Na2H2Y•2H2O)

Question 15

Form of EDTA that binds to metal ions

Answer 15

Fully deprotonated form (Y4-)

Question 16

Metal-EDTA complexes (MY4-) are unstable at extreme pH levels, thus EDTA titrations are usually carried out at _____ pH usually at _____.

Answer 16

Buffered pH at 10-12

Question 17

Second ligand called ______ is used to prevent the metal ion from precipitating. Forms weak complex with metal ion, and displaced by EDTA during titration

Answer 17

auxiliary complexing agent

Question 18

Which of the following are examples of auxiliary complexing agents

I. Ammonia
II. Citrate
III. Oxalate
IV. Tartrate or triethanolamine

Answer 18

I, II, IV

Question 19

Indicators used in complexation. These are organic dyes that form stable complexes with metal ions.

Answer 19

Metallochromic indicators

Question 20

True or false. Most metallochromic indicators are weak acids or bases thus, formation if metal-indicator complex (MIn^n-3) depends on pH.

Answer 20

True

Question 21

Common metallochromic indicators

Answer 21

EBT and Calmagite

Question 22

Commonly used in the determination of hardness in water

Answer 22

EDTA titrations

Question 23

Refers to the total concentration of polyvalent ions, mainly Ca2+ and Mg2+ in water. Commonly expressed in ppm CaCO3

Answer 23

Hardness

Question 24

During titration, _____ (M-indicator compex reacts with EDTA forming a more stable M-EDTA complex) occurs causing a change in color (freeing the ____).

Answer 24

Displacement, indicator

Question 25

This method of cyanide determination is the widely used complexometric titration using a monodentate ligand (CN-)

Answer 25

Liebig methods

Question 26

This method of cyanide determination is the widely used complexometric titration using s monodentate ligand (CN-)

Answer 26

Liebig methods

Question 27

During titration, the ratio of anyte (KCN) to titrant (AgNO3) is

Answer 27

2:1

Question 28

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 ____.

Answer 28

Silver nitrate (AgNO3) Dicyanoargentate (KAg(CN)2) Silver cyanide ( AgCN) Potassium iodide (KI) Silver iodide (AgI)