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CHEM 23 > complex formation equilibria > Flashcards

complex formation equilibria Flashcards

1
Q

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

A

metal complexes

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2
Q

molecules or ions surrounding a complex

A

ligand

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3
Q

ligand in latin and meaning

A

ligare = to bind

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4
Q

either an anion or polar molecule

A

ligand

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5
Q

contain at least one unshared pair of valence electron

A

ligand

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6
Q

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

A

coordinate covalent bond

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7
Q

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

A

coordination number

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8
Q

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

A

monodentate ligand

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9
Q

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

A

monodentate ligand

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10
Q

example of monodentate ligand

A

NH3

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11
Q

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

A

polydentate ligand

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12
Q

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

A

chelating agent in polydentate ligand

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13
Q

advantages multidentate ligands over unidentate

A

complexometric titrations

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14
Q

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

A

complexometric titrations

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15
Q

ordinarily react with metal ions in a single step process

A

complexometric titrations

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16
Q

complex formation with unidentate ligands usually involves how many intermediate species

A

two or more

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17
Q

among the most important and widely used reagent in titrimetry

A

EDTA

18
Q

what type of ligand is EDTA?

A

hexadentate

19
Q

what type of base is EDTA?

A

Lewis

20
Q

how many binding sites does EDTA have

A

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

21
Q

ratio of EDTA and all metals

A

1:1 stoichiometry

22
Q

is EDTA a base or an acid

A

EDTA is a weak acid that dissociates in water

23
Q

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

A

carboxylic group

24
Q

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

A

amine group

25
Q

what is the indicator for EDTA or complexation titrations

A

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

26
Q

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

A

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

27
Q

what are the metallochromic indicators

A
  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)
28
Q

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

A

required to prevent precipitation of the analyte

29
Q

what happens if there is a presence of ammonia

A

decreases the change in pZn near the equivalence point

30
Q

titration techniques

A
  1. direct titration
  2. back titration
  3. displacement titration
  4. indirect titration
31
Q

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

A

direct titration

32
Q

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

A

back titration

33
Q

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

A

to avoid displacement of analyte ion

34
Q

when are back titration used?

A
  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
35
Q

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

A

displacement titration

36
Q

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

A

displacement titration

37
Q

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

A

indirect titration

38
Q

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-

A

indirect titration

39
Q

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

A

masking

40
Q

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

A

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

CHEM 23 (7 decks)

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