# hard transition metal question

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#1
When cobalt (II) chloride is treated, under certain conditions, with the bidentate ligand, NH2CH2CH2NH2, (which can be represented by the symbol “en”), the compound [CoC12(en)2]Cl is formed.
(i) What is the oxidation state of cobalt in the compound formed? What is the co-ordination number of cobalt in this compound?
the markscheme says ox s is 3 and coordination number is 6, how do they get that? isn't cobalt +2?
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#2
When cobalt (II) chloride is treated, under certain conditions, with the bidentate ligand, NH2CH2CH2NH2, (which can be represented by the symbol “en”), the compound [CoC12(en)2]Cl is formed.
(i) What is the oxidation state of cobalt in the compound formed? What is the co-ordination number of cobalt in this compound?
the markscheme says ox s is 3 and coordination number is 6, how do they get that? isn't cobalt +2?
When hydrazine, NH2NH2, reacts with cobalt (II) chloride in aqueous solution, the compound CoCl2(NH2NH2)2 is formed. This compound has a polymeric structure in which cobalt is six co-ordinate and the cobalt ions are linked by hydrazine molecules. Draw the structure of the repeating unit of the polymer.

Deduce the structural formula of the complex compound CoCl3.4NH3, in which cobalt has the same oxidation state and co-ordination number as in [Co(NH3)6]Cl3
Last edited by usernamenew; 3 years ago
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3 years ago
#3
that is one tough nut to crack. the markscheme doesn't help as well. hopefully, someone can answer this.
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3 years ago
#4
[CoCl2(en)2]Cl
charge on Cl- ligands = -1
charge on en ligands = 0
charge on Cl- ion = -1
let charge on Co be x
x + 2(-1) + 2(0) -1 = 0
x = +3

Coordination number is 6

NH2NH2 has 1 lone pair on each N atom. One of the lone pairs is used to datively bond to the Co ion and the other one is used to bridge the ion to the next one, forming a polymeric structure. Draw the repeat unit

in [Co(NH3)6]Cl3
oxidation state is +3 and co-ordination number is 6

the compound is [Co(NH3)4Cl2]Cl
The NH3 must be bound to the central metal ion because they are uncharged and cannot balance out any charge remaining on the ion
One Cl- ion balances the charge of the [Co(NH3)4Cl2]+ ion

When hydrazine, NH2NH2, reacts with cobalt (II) chloride in aqueous solution, the compound CoCl2(NH2NH2)2 is formed. This compound has a polymeric structure in which cobalt is six co-ordinate and the cobalt ions are linked by hydrazine molecules. Draw the structure of the repeating unit of the polymer.

Deduce the structural formula of the complex compound CoCl3.4NH3, in which cobalt has the same oxidation state and co-ordination number as in [Co(NH3)6]Cl3
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3 years ago
#5
Oh shoot, i didn't realise the oxidation state was +3.
(Original post by BobbJo)
[CoCl2(en)2]Cl
charge on Cl- ligands = -1
charge on en ligands = 0
charge on Cl- ion = -1
let charge on Co be x
x + 2(-1) + 2(0) -1 = 0
x = +3

Coordination number is 6

NH2NH2 has 1 lone pair on each N atom. One of the lone pairs is used to datively bond to the Co ion and the other one is used to bridge the ion to the next one, forming a polymeric structure. Draw the repeat unit

in [Co(NH3)6]Cl3
oxidation state is +3 and co-ordination number is 6

the compound is [Co(NH3)4Cl2]Cl
The NH3 must be bound to the central metal ion because they are uncharged and cannot balance out any charge remaining on the ion
One Cl- ion balances the charge of the [Co(NH3)4Cl2]+ ion
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