complex formation equilibria

Question 1

assemblies of a central metal ion bounded to a group of surrounding molecule or ions

Answer 1

metal complexes

Question 2

molecules or ions surrounding a complex

Answer 2

ligand

Question 3

ligand in latin and meaning

Answer 3

ligare = to bind

Question 4

either an anion or polar molecule

Answer 4

ligand

Question 5

contain at least one unshared pair of valence electron

Answer 5

ligand

Question 6

what is the bond called when the central metal ion and the ligand bond

Answer 6

coordinate covalent bond

Question 7

what is the number of atoms directly bonded to the central atom called

Answer 7

coordination number

Question 8

contains only a lone pair hence it can donate only one electron pair per ligand

Answer 8

monodentate ligand

Question 9

possess only single donor atom per molecule and are able to occupy only one site in a coordination sphere

Answer 9

monodentate ligand

Question 10

example of monodentate ligand

Answer 10

NH3

Question 11

ligands that contain two or more atoms that can simultaneously coordinate to a central metal ions so they can occupy two or more coordination sphere

Answer 11

polydentate ligand

Question 12

they appear to grasp the metal between two or more donor atoms

Answer 12

chelating agent in polydentate ligand

Question 13

advantages multidentate ligands over unidentate

Answer 13

complexometric titrations

Question 14

generally react more completely with cations and thus provide sharper end points

Answer 14

complexometric titrations

Question 15

ordinarily react with metal ions in a single step process

Answer 15

complexometric titrations

Question 16

complex formation with unidentate ligands usually involves how many intermediate species

Answer 16

two or more

Question 17

among the most important and widely used reagent in titrimetry

Answer 17

EDTA

Question 18

what type of ligand is EDTA?

Answer 18

hexadentate

Question 19

what type of base is EDTA?

Answer 19

Lewis

Question 20

how many binding sites does EDTA have

Answer 20

six with fpur negatively charged carboxylate groups and two tertiary amino groups

Question 21

ratio of EDTA and all metals

Answer 21

1:1 stoichiometry

Question 22

is EDTA a base or an acid

Answer 22

EDTA is a weak acid that dissociates in water

Question 23

which group EDTA dissociates in the 1st and 2nd dissociation

Answer 23

carboxylic group

Question 24

which group EDTA dissociates in the 3rd and 4th dissociation

Answer 24

amine group

Question 25

what is the indicator for EDTA or complexation titrations

Answer 25

organic dyes known as matallochromic indicators that form stable complexes with metal ions

Question 26

if the indicator's color is red, blue, and orange

Answer 26

red: below 8 pH, blue: 7-11 pH, orange: above 12 pH

Question 27

what are the metallochromic indicators

Answer 27

1. calmagite (8.5-11 pH) 2. eriochrome Black T (7.5-10.5 pH) 3. eriochrome Blue Black T (8-12 pH) 4. murexide (6-13 pH) 5. PAN (2-11 pH) 6. salicylic acid (2-3 pH)

Question 28

why is the concentration of auxiliary complexing reagents should always be the minimum

Answer 28

required to prevent precipitation of the analyte

Question 29

what happens if there is a presence of ammonia

Answer 29

decreases the change in pZn near the equivalence point

Question 30

titration techniques

Answer 30

1. direct titration 2. back titration 3. displacement titration 4. indirect titration

Question 31

in this titration you simply add an indicator to a buffered solution of the metal ion and titrate with standard EDTA

Answer 31

direct titration

Question 32

in this titration, an excess of EDTA is added to the metal ion solution and the excess EDTA is titrated with a known concentration of a second metal ion

Answer 32

back titration

Question 33

why is the second metal ion in back titration must form a weaker complex with EDTA

Answer 33

to avoid displacement of analyte ion

Question 34

when are back titration used?

Answer 34

1. the metal ion blocks the indicator 2. when the metal-EDTA complex forms too slowly 3. when the metal precipitates in the absence of EDTA

Question 35

this is used for metal ions that do not have a good indicator

Answer 35

displacement titration

Question 36

the analyte is treated with an excess of a second metal bound to EDTA and the displaced second metal is titrated with EDTA

Answer 36

displacement titration

Question 37

EDTA can be used as a titrant for anions like SO4²-

Answer 37

indirect titration

Question 38

SO4²- is precipitated with Ba as insoluble BaSO4, the precipitate is wash then boil in excess EDTA to complex all the Ba²+, excess EDTA is then back titrated to determine how much Ba is present SO4²-

Answer 38

indirect titration

Question 39

auxiliary complexing agents can be added to keep metal ions in solution

Answer 39

masking

Question 40

CN-(cyanide) will form strong complexes with what?

Answer 40

Zn²+, Hg²+, Co²+, Cu+, Ag+, Ni²+, Pd²+, Pt²+, Fe²+, and Fe³+ but not Mg²+, Ca²+, Mn²+, Pb²+