Basic Terms Questions in English

(C) In a coordination complex,the central metal ion acts as a Lewis acid (electron pair acceptor) and the ligand acts as a Lewis base (electron pair donor).
In the complex $[Co(NH_3)_6]^{3+}$,the central metal ion is $Co^{3+}$ and the ligand is $NH_3$.
Therefore,$Co^{3+}$ acts as a Lewis acid and $NH_3$ acts as a Lewis base.

(A) $EDTA^{4-}$ is a hexadentate ligand,meaning it occupies $6$ coordination sites around a central metal ion.
Since $Ca^{2+}$ forms an octahedral complex with a coordination number of $6$,a single $EDTA^{4-}$ molecule is sufficient to satisfy all $6$ coordination sites.
Therefore,$1$ molecule of $EDTA$ is required.

(B) The chemical formula of cuprammonium sulfate is $[Cu(NH_3)_4]SO_4$.
When dissolved in water,it dissociates as follows:
$[Cu(NH_3)_4]SO_4 \rightleftharpoons [Cu(NH_3)_4]^{+2} + SO_4^{-2}$
Thus,it produces $2$ ions in the solution.

(B) The chemical formula for lithium aluminium tetrahydride is $Li[AlH_4]$.
In this complex,the central metal atom is $Al$ and the ligands attached to it are four hydride ions $(H^{-})$.
Therefore,the ligand present is $H^{-}$.

(C) According to Werner's coordination theory,the secondary valency of a metal ion in a coordination compound corresponds to the number of ligand donor atoms directly bonded to the central metal ion. This number is defined as the coordination number of the metal. Therefore,the coordination number is equal to the secondary valency.

(C) In the molecule $N(CH_2CH_2NH_2)_3$,there are four donor nitrogen atoms (one tertiary amine nitrogen and three primary amine nitrogens). Therefore,it acts as a tetradentate ligand.

(D) The compound $K_4[Fe(CN)_6]$ is a coordination complex salt.
Upon dissociation in an aqueous solution,it ionizes as follows:
$K_4[Fe(CN)_6] \rightarrow 4K^+ + [Fe(CN)_6]^{4-}$.
There are $4$ potassium ions $(K^+)$ and $1$ complex ion $([Fe(CN)_6]^{4-})$.
Therefore,the total number of ions produced is $4 + 1 = 5$.

(B) $EDTA$ (Ethylenediaminetetraacetate) is a hexadentate ligand.
It occupies all $6$ coordination sites of the central metal ion to form an octahedral complex.
Therefore,only $1$ molecule of $EDTA$ is required to form an octahedral complex with a $Ca^{2+}$ ion.

(B) $EDTA^{4-}$ stands for Ethylenediaminetetraacetate ion.
It is a hexadentate ligand.
As shown in the structure,it contains two nitrogen atoms (from the amine groups) and four oxygen atoms (from the four carboxylate groups) that can donate lone pairs to the central metal ion.
Therefore,the donor atoms are two $N$ and four $O$.

(C) The total number of coordinate bonds formed between the central metal ion and the ligands is defined as the coordination number of the metal ion. Therefore,the correct option is $C$.

(C) The coordination number is defined as the total number of sigma bonds formed by the central metal atom with the ligands.
In the complex $[Co(en)_2Br_2]Cl_2$:
$en$ (ethylenediamine) is a bidentate ligand,so $2 \times en$ provides $2 \times 2 = 4$ coordination sites.
$Br$ (bromide) is a monodentate ligand,so $2 \times Br$ provides $2 \times 1 = 2$ coordination sites.
Total coordination number = $4 + 2 = 6$.

(D) The chemical formula for ferric hexacyanoferrate $(II)$ is $Fe_4[Fe(CN)_6]_3$.
In an aqueous solution,it dissociates as follows:
$Fe_4[Fe(CN)_6]_3 (s) \rightarrow 4Fe^{3+} (aq) + 3[Fe(CN)_6]^{4-} (aq)$.
The total number of ions produced is $4 + 3 = 7$.

(A) The chemical formula of cisplatin is $[Pt(NH_3)_2Cl_2]$.
In this coordination complex,the central metal ion is $Pt^{2+}$.
The ligands attached to the central metal ion are ammonia $(NH_3)$ and chloride ions $(Cl^-)$.
Therefore,the correct option is $A$.

(D) Addition compounds are classified into two types: double salts and coordination compounds.
Double salts dissociate completely into their constituent ions when dissolved in water,losing their identity.
Coordination compounds (or complex compounds) do not dissociate completely into their constituent ions in solution; the central metal ion and the ligands remain bonded within the coordination sphere,thus retaining their identity in solution.
Therefore,both complex compounds and coordination compounds retain their identity.

(B) The compound $[Co(NH_3)_6]Cl_3$ is a coordination complex that dissociates in water as follows:
$[Co(NH_3)_6]Cl_3 \rightarrow [Co(NH_3)_6]^{3+} + 3Cl^-$
From the dissociation,we get $1$ complex cation $[Co(NH_3)_6]^{3+}$ and $3$ chloride anions $Cl^-$.
Total number of ions = $1 + 3 = 4$.

(C) In the complex $[Co(NH_3)_6]Cl_3$,there are $6$ ammonia $(NH_3)$ ligands.
Each $NH_3$ molecule contains $3$ covalent $N-H$ bonds.
Therefore,the total number of covalent bonds within the ligands is $6 \times 3 = 18$.

(A) The coordination number of a central metal atom is defined as the number of ligand donor atoms to which the metal is directly bonded.
In the complex $[Fe(CN)_6]^{3-}$,the $Fe^{3+}$ ion is bonded to $6$ cyanide $(CN^-)$ ligands.
Since $CN^-$ is a monodentate ligand,each $CN^-$ contributes $1$ to the coordination number.
Therefore,the coordination number of $Fe$ is $6 \times 1 = 6$.

(B) negative ligand is an anionic species that donates a pair of electrons to the central metal atom.
Among the given options,$SO_4^{2-}$ (sulfato) is a negatively charged ligand.
$H_2O$ (aqua),$CO$ (carbonyl),and $NO$ (nitrosyl) are neutral ligands.

(C) The complex is $[E(en)_2(C_2O_4)]NO_2$.
$en$ (ethylenediamine) is a bidentate ligand,so $2 \times en$ provides $2 \times 2 = 4$ coordination sites.
$C_2O_4^{2-}$ (oxalate) is a bidentate ligand,providing $2$ coordination sites.
Total coordination number = $4 + 2 = 6$.
Let the oxidation state of $E$ be $x$.
The charge on $en$ is $0$,the charge on $C_2O_4$ is $-2$,and the charge on $NO_2$ is $-1$.
$x + 2(0) + (-2) + (-1) = 0$
$x - 3 = 0$
$x = +3$.
Thus,the coordination number is $6$ and the oxidation state is $3$.

(C) neutral ligand is a ligand that carries no net electrical charge.
Among the given options:
$A$. Chloro $(Cl^-)$ is an anionic ligand with a charge of $-1$.
$B$. Hydroxo $(OH^-)$ is an anionic ligand with a charge of $-1$.
$C$. Ammine $(NH_3)$ is a neutral molecule with a net charge of $0$.
$D$. Oxalato $(C_2O_4^{2-})$ is an anionic ligand with a charge of $-2$.
Therefore,$NH_3$ is the correct neutral ligand.

(C) The chemical formula for cuprammonium sulfate is $[Cu(NH_3)_4]SO_4$.
In this complex ion $[Cu(NH_3)_4]^{2+}$,the copper ion is bonded to $4$ ammonia $(NH_3)$ ligands.
Since $NH_3$ is a monodentate ligand,the coordination number of copper is $4 \times 1 = 4$.

(B) The coordination number is defined as the number of ligand donor atoms to which the metal is directly bonded.
In $[Fe(CN)_6]^{4-}$,there are $6$ $CN^-$ ligands,so the coordination number is $6$.
In $[Fe(CN)_6]^{3-}$,there are $6$ $CN^-$ ligands,so the coordination number is $6$.
In $[FeCl_4]^{-}$,there are $4$ $Cl^-$ ligands,so the coordination number is $4$.
Therefore,the coordination numbers are $6, 6, 4$.

(C) The coordination number is defined as the number of ligand donor atoms directly bonded to the central metal ion. In the complex $[CoF_6]^{3-}$,there are $6$ fluoride $(F^-)$ ions bonded to the central cobalt $(Co)$ ion. Since $F^-$ is a monodentate ligand,the coordination number is $6$.

(B) ligand that can form a chelate is known as a chelating ligand,which must be a polydentate ligand.
Among the given options,$Acetate$,$Cyanide$,and $Ammonia$ are monodentate ligands.
$Oxalate$ $(C_2O_4^{2-})$ is a bidentate ligand that can coordinate through two donor oxygen atoms to form a stable five-membered ring structure with the central metal ion,thus forming a chelate.

(C) In a coordination complex,the ligands (such as $NH_3$) donate a lone pair of electrons to the central metal atom (such as $Co^{3+}$).
This type of bond,where both electrons are provided by one atom,is known as a coordinate covalent bond or simply a coordinate bond.

(D) $1$. The coordination number is the total number of ligand donor atoms bonded to the central metal atom. Here,$SO_4^{2-}$ acts as a bidentate ligand (or monodentate depending on coordination,but in standard coordination chemistry nomenclature for this complex,it is treated as occupying one coordination site as a monodentate ligand in the inner sphere) and $5$ $NH_3$ molecules are monodentate. Thus,$CN = 1 + 5 = 6$.
$2$. To find the oxidation state of $X$,let it be $x$. The charge on $SO_4$ is $-2$ and $NH_3$ is $0$. Assuming the complex is neutral,$x + (-2) + 5(0) = 0$,so $x = +2$.
$3$. Therefore,the coordination number is $6$ and the oxidation state is $2$.

(C) The ligand $N[CH_2CH_2NH_2]_3$ is known as $tren$ (tris($2$-aminoethyl)amine).
It contains one tertiary amine nitrogen atom and three primary amine nitrogen atoms.
All four nitrogen atoms have lone pairs available for donation to the central metal ion.
Therefore,it acts as a tetradentate ligand.

(D) chelating agent is a polydentate ligand that can form a ring structure with a central metal atom.
$EDTA^{4-}$ is a hexadentate ligand,$en$ is a bidentate ligand,and oxalate is a bidentate ligand; all of these can form chelate rings.
Pyridine $(C_5H_5N)$ is a monodentate ligand,meaning it binds to the metal atom through only one donor atom (nitrogen) and cannot form a ring structure.
Therefore,pyridine is not a chelating agent.

(D) The complex $Co(NH_3)_5Cl_3$ reacts with $2$ moles of $AgNO_3$ to form $2$ moles of $AgCl(s)$,which indicates that there are $2$ chloride ions outside the coordination sphere.
Thus,the formula is $[Co(NH_3)_5Cl]Cl_2$.
Upon dissolution,it ionizes as: $[Co(NH_3)_5Cl]Cl_2 \rightarrow [Co(NH_3)_5Cl]^{2+} + 2Cl^-$.
This gives a total of $1 + 2 = 3$ moles of ions,which matches the given information.

(B) The coordination number of a central metal atom is the total number of sigma bonds formed by the ligands with the central metal atom.
In the complex $[Co(NH_3)_4Cl_2]Cl$,the central metal atom is $Co^{3+}$.
The ligands attached are $4$ molecules of $NH_3$ (monodentate) and $2$ ions of $Cl^-$ (monodentate).
Coordination number = $(4 \times 1) + (2 \times 1) = 6$.

(C) The complex $[Cu(NH_3)_4]SO_4$ dissociates in water as $[Cu(NH_3)_4]SO_4 \rightarrow [Cu(NH_3)_4]^{2+} + SO_4^{2-}$.
Since the $SO_4^{2-}$ ion is present in the ionization sphere (outside the coordination entity),it is free to react and will give a positive test for sulfate ions (e.g.,with $BaCl_2$ solution).
The $Cu^{2+}$ and $NH_3$ are part of the coordination sphere $[Cu(NH_3)_4]^{2+}$ and do not dissociate,so they do not give their characteristic tests.

(A) The $SCN^-$ ion is an ambidentate ligand.
When the sulfur atom is bonded to the central metal,it is named as $Thiocyanato-S$.
When the nitrogen atom is bonded to the central metal,it is named as $Isothiocyanato-N$ (or $Thiocyanato-N$).

(C) The chemical formula for dichlorodioxalatochromium$(III)$ is $[Cr(C_2O_4)_2Cl_2]^-$.
Primary valency corresponds to the oxidation state of the central metal atom. Here,for $Cr$,let it be $x$: $x + 2(-2) + 2(-1) = -1 \implies x - 4 - 2 = -1 \implies x = +3$.
Secondary valency corresponds to the coordination number. Since oxalate is a bidentate ligand $(2 \times 2 = 4)$ and chloride is a monodentate ligand $(2 \times 1 = 2)$,the total coordination number is $4 + 2 = 6$.
Thus,the primary and secondary valencies are $3$ and $6$ respectively.

(D) $1$. Reaction with excess $AgNO_3$: Only the chloride ions outside the coordination sphere will precipitate as $AgCl$.
$[Co(NH_3)_5Br]Cl_2$ provides $2 \times 0.02 = 0.04 \ mol$ of $Cl^-$.
$[Co(NH_3)_5Cl]SO_4$ does not provide any $Cl^-$ ions outside the coordination sphere.
Thus,moles of $AgCl$ $(Y)$ = $0.04 \ mol$.
$2$. Reaction with excess $BaCl_2$: Only the sulfate ions outside the coordination sphere will precipitate as $BaSO_4$.
$[Co(NH_3)_5Cl]SO_4$ provides $0.02 \ mol$ of $SO_4^{2-}$.
$[Co(NH_3)_5Br]Cl_2$ does not provide any $SO_4^{2-}$ ions.
Thus,moles of $BaSO_4$ $(Z)$ = $0.02 \ mol$.

(D) The coordination compound $[Co(NH_3)_3Cl_3]$ is a neutral complex.
In this complex,all ligands are inside the coordination sphere.
Therefore,it does not dissociate into ions in an aqueous solution.
Thus,the number of moles of ions produced is $0$,but since the complex itself remains as $1$ mole of undissociated species,the total number of particles/ions is $1$.

(D) The coordination compound $[Pt(NH_3)_6]Cl_4$ dissociates in water as follows:
$[Pt(NH_3)_6]Cl_4 \rightarrow [Pt(NH_3)_6]^{4+} + 4Cl^-$
From the dissociation,we get $1$ complex cation $[Pt(NH_3)_6]^{4+}$ and $4$ chloride anions $Cl^-$.
Total number of ions = $1 + 4 = 5$.

(D) According to Werner's theory,the primary valency corresponds to the oxidation state of the central metal ion,which is satisfied by the ionizable anions ($Cl^-$ ions).
For $(A) \ [Co(NH_3)_6]Cl_3$,the oxidation state of $Co$ is $+3$.
For $(B) \ [Co(NH_3)_5Cl]Cl_2$,the oxidation state of $Co$ is $+3$.
For $(C) \ [Co(NH_3)_4Cl_2]Cl$,the oxidation state of $Co$ is $+3$.
Thus,the primary valency for all three complexes is $3$.

(B) $H_2N - CH_2 - CH_2 - NH_2$ is ethylenediamine $(en)$.
It is a bidentate ligand that forms a stable five-membered ring with the central metal atom.
Therefore,it acts as a chelating ligand.

(D) $[EDTA]^{4-}$ stands for Ethylenediaminetetraacetate ion. It has $6$ donor atoms ($2$ nitrogen atoms and $4$ oxygen atoms) that can coordinate to a central metal ion simultaneously. Therefore,it is a hexadentate ligand.

(D) ligand is defined as an ion or a molecule that is bound to the central metal atom or ion in a coordination entity.
These ligands donate a pair of electrons to the central metal atom or ion to form a coordinate covalent bond.
Therefore,ligands can be anions,cations,or neutral molecules.

(A) $1$. The coordination number is determined by the number of donor atoms directly bonded to the central metal ion. Here,$4$ $H_2O$ molecules (monodentate) and $1$ $SO_3^{2-}$ ion (monodentate) are bonded,so the coordination number is $4 + 1 = 6$.
$2$. To find the oxidation state of $Co$,let it be $x$. The charge on $H_2O$ is $0$,$SO_3$ is $-2$,and $Cl$ is $-1$. Thus,$x + 4(0) + 1(-2) + 1(-1) = 0$,which gives $x = +3$.
$3$. The electronic configuration of $Co$ $(Z=27)$ is $[Ar] 3d^7 4s^2$. For $Co^{3+}$,it is $[Ar] 3d^6$.
$4$. In the presence of strong field ligands like $SO_3^{2-}$,the $d$-electrons in $Co^{3+}$ $(3d^6)$ pair up in the $t_{2g}$ orbitals,resulting in $0$ unpaired electrons.

(A) According to Werner's coordination theory:
$1$. Primary valency corresponds to the oxidation state of the central metal ion and is ionizable.
$2$. Secondary valency corresponds to the coordination number of the central metal ion and is non-ionizable.
Therefore,the statement that primary valency is ionizable is correct.

(B) The coordination compound $[Co(NH_3)_5Cl]Cl_2$ ionizes in water as follows:
$[Co(NH_3)_5Cl]Cl_2 \rightarrow [Co(NH_3)_5Cl]^{2+} + 2Cl^-$.
There are $2$ moles of ionizable chloride ions $(Cl^-)$ outside the coordination sphere for every $1$ mole of the complex.
The total number of chlorine atoms in the formula is $3$ ($1$ inside the coordination sphere and $2$ outside).
The fraction of chlorine that can be precipitated by $AgNO_3$ is the ratio of ionizable $Cl^-$ ions to the total number of $Cl$ atoms.
Fraction = $\frac{2}{3}$.

(D) double salt dissociates completely into its constituent ions in an aqueous solution,whereas a coordination compound retains its identity and does not dissociate completely into its constituent ions.
$KCl \cdot MgCl_2 \cdot 6H_2O$ (Carnallite),$FeSO_4 \cdot (NH_4)_2SO_4 \cdot 6H_2O$ (Mohr's salt),and $K_2SO_4 \cdot Al_2(SO_4)_3 \cdot 24H_2O$ (Potash alum) are all double salts.
$4KCN \cdot Fe(CN)_2$ is equivalent to $K_4[Fe(CN)_6]$,which is a coordination compound (Potassium ferrocyanide) that does not dissociate into $Fe^{2+}$ and $CN^-$ ions in water.

(D) The chemical formula for tetraamminedichloroplatinum $(IV)$ chloride is $[Pt(NH_3)_4Cl_2]Cl_2$.
In coordination chemistry,the secondary valency of a central metal ion is equal to its coordination number.
The coordination number is the total number of ligand donor atoms bonded directly to the central metal ion.
Here,the central metal ion is $Pt^{4+}$.
It is bonded to $4$ $NH_3$ molecules (monodentate) and $2$ $Cl^-$ ions (monodentate).
Therefore,the coordination number = $4 + 2 = 6$.
Thus,the secondary valency is $6$.

(B) $\pi$-acid ligands (also known as $\pi$-acceptor ligands) are ligands that can accept electron density from the metal atom into their empty $\pi^*$ antibonding orbitals.
$CO$ (carbon monoxide) is a classic example of a $\pi$-acid ligand because it possesses empty $\pi^*$ orbitals that can accept electron density from the metal $d$-orbitals via back-bonding.
$NH_3$,$F^{-}$,and ethylenediamine are $\sigma$-donor ligands.

(D) $1$. The ligand '$en$' stands for ethylenediamine $(NH_2CH_2CH_2NH_2)$,which is a bidentate ligand.
$2$. The coordination number $(C.N)$ is calculated as: $(\text{number of ligands}) \times (\text{denticity}) = 2 \times 2 = 4$.
$3$. Let the oxidation state of $Pt$ be $x$. The charge on ethylenediamine is $0$.
$4$. The equation for the complex is: $x + 2(0) = +2$,which gives $x = +2$.
$5$. Therefore,the coordination number is $4$ and the oxidation state is $+2$.

(B) An ambidentate ligand is a ligand that can coordinate to the central metal atom through two different donor atoms.
$CN^-$ is an ambidentate ligand because it can coordinate through the carbon atom ($M-CN$,cyano) or through the nitrogen atom ($M-NC$,isocyano).
Therefore,the correct option is $B$.