Complexometry ✅ Flashcards
What is complexometry?
volumetric analytic method based on titration of metal ion solutions with a substance that, combined with metal ions, yields complex compounds.
Are complex compounds coloured?
some are, yet complex compounds do not have to be coloured.
What changes occur during the formation of complexes?
No visible changes, no changes in properties, no precipitate, no colour change.
What is the structure of complex compounds?
- central metal atom
- surrounded by ions/molecules called ligands
ligand: electron donor
What is a complex compound called when it is charged?
a complex ion
What are ligands?
- typically anions or polar molecules.
- must have line pairs of electrons to interact with metals.
What do coordinate covalent bonds need?
a donor atom (which donated electrons)
What does the number of electron pairs a metal ion is capable of recieving depends on?
- its radius
- electron configuration
- structure of the ligand
What is a coordination number?
the number of atoms or ions immediately surrounding a central atom in a complex or crystal.
What is coordination?
When an orbital from a ligand with lone pairs in it overlaps with an empty orbital from a metal.
When is the complex most stable?
In its symmetrical structure.
How is a metal-ligand bond formed?
between a lewis acid and lewis base
What lewis is a metal?
lewis acid (accepts electrons)
What lewis is a ligand?
lewis base (donates electrons)
What is a mixed complex?
more than one type of ligand present in a complex
What are multi-center complexes?
complexes with 2+ central metal ions.
In coordination compounds, what type of valency do central metal atoms exhibit?
- primary valency (oxidation state)
- secondary valency (coordination number)
What is a monodentate complex?
If there is only one donor atom in the ligand.
What is a bidentate complex?
If there are two donor atom in the ligand.
What valency do all metal atoms have fixed?
number of secondary valencies
Why do compounds have definite geometry?
The coordination number of secondary valencies is always directed towards fixed positions in space.
What is A, B, and C?
A[B(C)x]
A- second coordination sphere
B- central metal ion
C- ligand
x- coordination number
[B(C)]- first coordination sphere
A- second coordination sphere
When is the formula of [complex ions (primary coordination sphere)] put before the secondary coordination sphere? When after?
before: if the [] is positive
after: if the [] is negative
How to name complex compounds?
1) coordination number (mono-, di-, tri- and etc.)
2) ligand
3) metal ion with valency state
eg. [Ag(NH3)2]+: diammine-silver (I) ion
[Ni(H20)6]2+:hexaaqua-nickel (II) ion
How to name complex anions?
1) coordination number (mono-, di-, tri- and etc.)
2) ligand
3) metal ion with valency state, **add “-ATE” to metal **
eg. [Al(OH)4]: tetrahydroxo-aluminate (III) ion
[Cu(NH3)4]SO4: [tetraamine-copper (II)]- sulphate
What is a complexone? What is a complexonate?
- any chylating agent used for the analytical determination of metals.
- form stable complex compounds with numerous ions of metals
What is a chelating agent?
organic compounds which complex metal ions.
- removes a metallic ion from a solid salt and holds it in solution.
(catch ions to stabilize the system)
What is a common complexonate? What is it most commonly used for?
EDTA
- determining of water hardness
water hardness: Mg 2+ and Ca2+
What are the two types of metal hardnesses?
1) temporary (carbonate hardness)
2) permanent (non-carbonate hardness)
What is temporary hardness?
casued by Ca(HCO3)2 and Mg(HCO3)2
What is permanent hardness?
caused by Ca2+/Mg2+ sulfates, chlorides, silicates, -phosphates and nitrates.
What is “water softening”?
The elimination of calcium and magnesium salts from water.
Water hardness titration.
indicator: eriochrome black T
colour change: red (chelated) –> blue (not chelated)
How can temporary hardness be eliminated?
by water boiling
CaCO3 precipitates, but has to be removed or it will dissolve again.
How can permanent water hardness be removed?
- not by boiling!
- slacked lime
- soda
- sodium phosphate
- borax
- exchangers (ionites): SODIUM AND HYDROGEN CATIONITES
