Coordination Compounds Class 12 Chemistry Important Questions

Important Questions Class 12

Please refer to Coordination Compounds  Class 12 Chemistry Important Questions with solutions provided below. These questions and answers have been provided for Class 12 Chemistry based on the latest syllabus and examination guidelines issued by CBSE, NCERT, and KVS. Students should learn these problem solutions as it will help them to gain more marks in examinations. We have provided Important Questions for Class 12 Chemistry for all chapters in your book. These Board exam questions have been designed by expert teachers of Standard 12.

Class 12 Chemistry Important Questions Coordination Compounds 

Very Short Answer Questions

Question. What is the coordination number and the oxidation state of the metal in each of the following complexes?
(a) [AgCl2]   (b) [Cr(H2O)5Cl]2+   (c) [Co(NCS)4]2–
(d) [Co(NH3)3(NO2)3]   (e)[Fe(EDTA)]–   (f) [Cu(en)2]SO4
Answer.
The coordination number of the central atom/ion is determined by the number of sigma bonds between the ligands and the central atom/ions i.e. the number of ligand donor atoms to which the metal is directly attached. The oxidation number of the central atom is defined as the charge it would carry if all the ligands are removed along with the electron pairs that are shared with the central atom. Complex Coordination Number and Oxidation State respectively are:
(a) 2 ,1  (b) 6, 3  (c) 4 ,2
(d) 6, 3  (e) 6, 3  (f) 4, 2

Question. Write down the formulae of the following compounds
(a) diamminetriaquahydroxidochromium (III) nitrate
(b) tetrakis(pyridine)platinum(II) tetraphenylborate(III)
(c) dibromidotetracarbonyliron (II)
(d) ammonium diamminetetrakis(isothiocyanato)chromate(III).
Answer.(a) [Cr(NH3)2(H2O)3(OH)](NO3)2
(b) [Pt(Py)4][B(ph)4]2
(c) [Fe(Br)2(CO)4]
(d) (NH4)[Cr(NH3)2(NCS)4].

Question. The magnetic moment of [MnBr4]2– is 5.9 B.M. What is the geometry of this complex ion?
Answer.
Since the coordination number of Mn2+ ion in this complex ion is 4, it may be either tetrahedral (sp3 hybridisation) or square planar (dsp2 hybridisation) as shown below at (b) and (c). But the fact that the magnetic moment of the complex ion is 5.9 B.M. shows that it should be tetrahedral in shape rather than square-planar.

Coordination Compounds Class 12 Chemistry Important Questions

Question. Complete the following statements for the coordination entity (complex ion) [CrCl2(OX)2]3-
(a) OX is abbreviation for ____________
(b) The oxidation number of chromium is ____________
(c) The coordination number of chromium is ____________
Answer.
a) oxalato (b) +3 (c) 6

Question. Write down the IUPAC nomenclature of the given complex along with its hybridisation and structure.
Answer.
K2[Cr(NO)(NH3)(CN)4] ; μ = 1.73 B.M.
(Potassium amminetetracyanonitrosoniumchromate(I) Cr is in +1 oxidation state and possess d2sp3 hybridisation with one unpaired electron.

Coordination Compounds Class 12 Chemistry Important Questions

Question. Draw figure to show the splitting of d orbitals in an octahedral crystal field.
Answer.

Coordination Compounds Class 12 Chemistry Important Questions

Question. When a co-ordination compound CrCl3⋅6H2O is mixed with AgNO3, 2 moles of AgCl are precipitated per mole of the compound. Write structural formula of the complex.
Answer. For one mole of the compound, two moles of AgCl are precipitated which indicates that two ionisable chloride ions in the complex. Hence, its structural formula is [CrCl(H2O)5]Cl2.H2O

Question. When a coordination compound CoCl3⋅6NH3 is mixed with AgNO3, 3 moles of AgCl are precipitated per mole of the compound. Write structural formula of the complex.
Answer. Structural formula : [Co(NH3)6]Cl3

Question. What do you understand by ‘denticity of a ligand’?
Answer. Denticity : The number of coordinating groups present in a ligand is called the denticity of ligand. For example, bidentate ligand ethane-1, 2-diamine has two donor nitrogen atoms which can link to central metal atom.
                            H2N CH2 CH2 NH2
                            Ethane-1, 2-diamine

Question. Giving a suitable example, explain the following :
Ambidentate ligand
Answer. Ambidentate ligand : A unidentate ligand which can coordinate to central metal atom through two different atoms is called ambidentate ligand. For example NO2 ion can coordinate either through nitrogen or through oxygen to the central metal atom/ion.

Question. What is meant by chelate effect?
Answer. When a di– or polydentate ligand uses its two or more donor atoms to bind a single metal ion. It is said to be a chelate ligand. Chelating ligands form more stable complexes than monodentate analogs. This is called chelating effect.

Question. Write the IUPAC name of [Co(NH3)5Cl]Cl2.
(Atomic no. of Co = 27)
Answer. Pentaamminechloridocobalt (III) chloride.

Question. Using the IUPAC norms, write the systematic name of following :
[CoCl(NO2)(NH3)4]Cl
Answer. Tetraamminechloridonitrito-N-cobalt (III) chloride.

Question. Write down the IUPAC name of the complex [Pt(en)2Cl2]2+. What type of isomerism is shown by this complex?
Answer. IUPAC name – Dichloridobis(ethane-1,2-diamine) platinum (IV) ion. This complex shows geometrical and optical isomerism.

Coordination Compounds Class 12 Chemistry Important Questions

Question. Draw the geometrical isomers of complex [Pt(en)2Cl2]2+.
Answer. 

Coordination Compounds Class 12 Chemistry Important Questions

Question. What type of isomerism is exhibited by the complex [Co(en)3]3+? (en = ethane-1,2-diamine)
Answer. 

Coordination Compounds Class 12 Chemistry Important Questions

Question. What type of isomerism is shown by the following complex :
[Co(NH3)6][Cr(CN)6]
Answer. Coordination isomerism : Its coordination isomer [Cr(NH3)6][CO(CN)6], in which NH3 ligands are bound to Cr3+ and CN ligands to Co3+.

Question. What type of isomerism is exhibited by the following complex :
[Co(NH3)5SO4]Cl
Answer. Ionisation isomerism : [Co(NH3)5SO4]Cl and [CO(NH3)5 Cl] SO4

Question. What type of isomerism is exhibited by the complex [Co(NH3)5NO2]2+?
Answer. Linkage isomerism : [Co(NH3)5NO2]2+ and [Co(ONO) (NH3)5]2+

Question. Indicate the types of isomerisms exhibited by the complex [Co(NH3)5(NO2)](NO3)2.
(At no. Co = 27)
Answer. (i) Ionisation isomers :
Co(NH3)5(NO2)2 and Co(NH3)5(NO3)(NO3)
(ii) Linkage isomers :
Co(NH3)5(NO2)2 and Co(NH3)5(ONO)2

Question. Giving a suitable example, explain the following :
Linkage isomerism
Answer. Linkage isomerism : Linkage isomerism arises in a coordination compound containing ambidentate ligand. A simple example is provided by complexes containing the thiocyanate ligand, NCS which may bind through the nitrogen to give M-NCS or through sulphur to give M-SCN. This behaviour was seen in the complex [Co(NH3)5(NO2)]Cl2, which is obtained as the red form, in which the nitrite ligand is bound through oxygen (–ONO), and as the yellow form, in which the nitrite ligand is bound through nitrogen (–NO2).

Question. Square planar complexes (of MX2L2 type) with coordination number of 4 exhibit geometrical isomerism whereas tetrahedral complexes with similar composition, do not. Why?
Answer. The tetrahedral complexes do not show geometrical isomerism because the relative positions of the atoms with respect to each other will be the same.

Question. Why is [NiCl4]2– paramagnetic but [Ni(CO)4] is diamagnetic? (At. no. : Cr = 24, Co = 27, Ni = 28)
Answer. [NiCl4]2– contains Ni2+ ion with 3d8 configuration.

Coordination Compounds Class 12 Chemistry Important Questions

The complex has all paired electrons hence, it is diamagnetic.

Short Answer Questions

Question. (i) Write down the IUPAC name of the following complex :
[Cr(NH3)2Cl2(en)]Cl (en = ethylenediamine)
(ii) Write the formula for the following complex :
Answer. (i) Diamminedichlorido (ethane-1,2-diamine) chromium(III) chloride.
(ii) [Co(NH3)5(ONO)]2+

Question. Using IUPAC norms write the formulae for the following coordination compounds :
(i) Hexaamminecobalt(III)chloride
(ii) Potassiumtetrachloridonickelate(II)
Answer.(i) [Co(NH3)6]Cl3
(ii) K2[NiCl4]

Question. Give the formula of each of the following coordination entities :
(i) Co3+ ion is bound to one Cl, one NH3 molecule and two bidentate ethylene diamine (en) molecules.
(ii) Ni2+ ion is bound to two water molecules and two oxalate ions.
Write the name and magnetic behaviour of each of the above coordination entities.
(At. nos. Co = 27, Ni = 28)
Answer. (i) [Co(en)2Cl(NH3)]2+
Amminechloridobis(ethane-1,2-diamine) cobalt(III)ion
In presence of strong NH3 and en ligand, Co3+(3d6) forms low spin complex. Hence, complex isdiamagnetic.
(ii) [Ni(ox)2(H2O)2]2– : Diaquadioxalato nickelate(II) ion In the presence of weak ox and H2O ligand, Ni(II) forms high spin complex (sp3d2 hybridisation). It is paramagnetic.

Question. [Fe(H2O)6]3+ is strongly paramagnetic whereas
[Fe(CN)6]3– is weakly paramagnetic. Explain
(At. no. Fe = 26]
Answer. In presence of CN, the 3d electrons pair up leaving only one unpaired electron, the hybridisation is d2sp3 forming an inner orbital octahedral complex whereas in the presence of H2O, 3d electrons do not pair up. The hydridisation is sp3d2 forming an outer orbital octahedral complex containing five unpaired electrons. Hence, it is strongly paramagnetic.

Question. Give the name, the stereochemistry and the magnetic behaviour of the following complexes :
(i) [Co(NH3)5Cl]Cl2 (ii) K2[Ni(CN)4]
Answer. (i) [Co(NH3)5Cl]Cl2 : Pentaamminechlorido cobalt (III) chloride.
Co(III) : [Ar]3d64s0 : d2sp3 hybridisation leads to octahedral shape.
Magnetic behaviour : Diamagnetic.
Stereochemistry : Complex [Co(NH3)5Cl]Cl2 do not exhibit geometrical and optial isomerism.
(ii) K2[Ni(CN)4] : Potassiumtetracyanonickelate(II)
Ni(II) : [Ar] 3d84s0 – dsp2 hybridisation leads to square planar shape.
Magnetic behaviour : Diamagnetic.
Stereochemistry : Complex [Ni(CN)4) do not exhibit geometrical isomerism and optical isomerism because all the possible arrangement are equivalent.

Question. Describe the type of hybridization, shape and magnetic property of [Co(NH3)4Cl2]+.
[Given : At. no. of Co = 27]
Answer. 

Coordination Compounds Class 12 Chemistry Important Questions

In this complex, Co is d2sp3 hybridised because NH3 is strong field ligand.

Coordination Compounds Class 12 Chemistry Important Questions

Question. How is the stability of a co-ordination compound in solution decided? How is the dissociation constant of a complex defined?
Answer. The stability of a complex in solution refers to the degree of association between the two species involved in the state of equilibrium. The magnitude of the equilibrium constant for the association, quantitatively expresses the stability. The instability constant or dissociation constant of coordination compound is defined as the reciprocal of the formation constant.

Question. What do you understand by stepwise stability constant and overall stability constant of a coordination compound? How are these two constants related?
Answer. Stability constant of each step of complex formation reaction is called stepwise stability constant. It is denoted by K. Stability constant of overall complex formation reaction is called overall stability constant. It is denoted by b.
The stepwise and overall stability constant are therefore related as follows:
b4 = K1 × K2 × K3 × K4 or more generally,
bn = K1 × K2 × K3 × K4 … Kn

Question. Describe with an example of each, the role of coordination compounds in :
(a) Biological systems
(b) Analytical chemistry
(c) Medicinal chemistry
Answer. (a) Biological systems : Coordination compounds are of great importance in biological systems. The pigment responsible for photosynthesis, chlorophyll, is a coordination compound of magnesium. Haemoglobin, the red pigment of blood which act as oxygen carrier is a coordination compound of iron. Vitamin B12, cyanocobalamine, the anti-pernicious anaemia factor, is a coordination compound of cobalt.
(b) Analytical Chemistry : Coordination compounds find use in many qualitative and quantitative chemical analysis. The familiar colour reactions given by metal ions with a number of ligands (especially chelating ligands), as a result of formation of coordination entities, form the basis for their detection and estimation by classical and instrumental methods of analysis. Examples of such reagents include EDTA, DMG (dimethylglyoxime), a-nitroso-b-naphthol, cupron, etc.
(c) Medicinal Chemistry : There is growing interest in the use of chelate therapy in medicinal chemistry. An example is the treatment of problems caused by the presence of metals in toxic proportions in plant/ animal system. Thus, excess of copper and iron are removed by the chelating ligands D-penicillamine and desferrioxime-B via the formation of coordination compounds. EDTA is used in the treatment of lead poisoning. Some coordination compounds of platinum effectively inhibit the growth of tumours. Examples are : cis-platin and related compounds.

Long Answer Questions

Question. What is meant by crystal field splitting energy?
On the basis of crystal field theory, write the electronic configuration of d4 in terms of t2g and eg in an octahedral field when
(i) Δo > P (ii) Δo < P
Answer. 
(i) The difference of energy between two states of splitted d-orbitals is called crystal field splitting energy. It is denoted by Δ or 10 Δq.
For octahedral Do, for tetrahedral it is Δt and for square planar Δsp.

Coordination Compounds Class 12 Chemistry Important Questions

Question. Name the following coordination entities and describe their structures.
(i) [Fe(CN)6]4– (ii) [Cr(NH3)4Cl2]+
(iii) [Ni(CN)4]2–
Answer. 
(i) [Fe(CN)6]4– : Hexacyanidoferrate(II) ion
Hybridisation – d2sp3
Structure : Inner orbital octahedral complex

Coordination Compounds Class 12 Chemistry Important Questions

Question. Write the name, stereochemistry and magnetic behaviour of the following : (At. nos. Mn = 25, Co = 27, Ni = 28)
(i) K4[Mn(CN)6] (ii) [Co(NH3)5Cl]Cl2
(iii) K2[Ni(CN)4]
Answer. 

Coordination Compounds Class 12 Chemistry Important Questions

Question. For the complex [Fe(en)2Cl2]Cl, identify the following :
(i) Oxidation number of iron
(ii) Hybrid orbitals and shape of the complex
(iii) Magnetic behaviour of the complex
(iv) Number of its geometrical isomers
(v) Whether there may be optical isomer also.
(vi) Name of the complex.
Answer. 
(i) [Fe(en)2Cl2]Cl
x + 0 × 2 + (–1) × 2 + (–1) × 1 = 0            x = 3
Oxidation number of iron = 3
(ii) d2sp3 hybridisation and octahedral shape.
(iii) Paramagnetic due to presence of one unpaired electron.
(iv) 2, cis and trans isomers.
(v) cis-[Fe(en)2Cl2] has optical isomer.
(vi) dichloridobis(ethane-1,2-diamine)iron(III)chloride

Coordination Compounds Class 12 Chemistry Important Questions

Question. Write the IUPAC name, deduce the geometry and magnetic behaviour of the complex
K4[Mn(CN)6].
[Atomic no. of Mn = 25]
Answer. 

Coordination Compounds Class 12 Chemistry Important Questions

IUPAC name : Potassium hexacyanomanganate (II)
Geometry : Octahedral
No. of unpaired electrons, n = 1
Magnetic behaviour : paramagnetic.

Question. Compare the following complexes with respect to their shape, magnetic behaviour and the hybrid orbitals involved :
(i) [CoF4]2–
(ii) [Cr(H2O)2(C2O4)2]
(iii) [Ni(CO)4]
(Atomic number : Co = 27, Cr = 24, Ni = 28)
Answer. 

Coordination Compounds Class 12 Chemistry Important Questions

Question. Compare the following complexes with respect to structural shapes of units, magnetic behaviour and hybrid orbitals involved in units :
[Co(NH3)6]3+, [Cr(NH3)6]3+, Ni(CO)4
(At. nos. : Co = 27, Cr = 24, Ni = 28)
Answer. 

Coordination Compounds Class 12 Chemistry Important Questions

Question. Explain the following :
(i) Low spin octahedral complexes of nickel are not known.
(ii) The p-complexes are known for transition elements only.
(iii) CO is a stronger ligand than NH3 for many metals.
Answer. 
(i) Nickel forms octahedral complexes mainly in +2 oxidation state which has 3d8 configuration.
In presence of strong field ligand also it has two unpaired electrons in eg orbital.

Coordination Compounds Class 12 Chemistry Important Questions

Hence, it does not form low spin octahedral complexes.
(ii) The transition metals/ions have empty d orbitals into which the electron pairs can be donated by ligands containing p electrons.
For example : CH2 CH2 and C6H6, C5H5–.
(iii) Co is stronger ligand than NH3 because CO has vacant molecular orbitals with which it can form p-bond with metal through back donation.

Question. Compare the following complexes with respect to structural shapes of units, magnetic behaviour and hybrid orbitals involved in units :
(i) [Ni(CN)4]2– (ii) [NiCl4]2–
(iii) [CoF6]3–
[At. nos. : Ni = 28; Co = 27]
Answer. 

Coordination Compounds Class 12 Chemistry Important Questions

Question. What will be the correct order for the wave lengths of absorption in the visible region for the following :
[Ni(NO2)6]4–, [Ni(NH3)6]2+, [Ni(H2O)6]2+
Answer. 
All the complex ions are derived from Ni2+ ion with different ligands. From the position of the ligands in the spectrochemical series the order of field strength is H2O < NH3 < NO2–
That means Do for NO2– is maximum and so it would absorb the radiation of shorter wavelength having high energy. So, the order of absorption of the correct wavelengths is
[Ni(H2O)6]2+ > [Ni(NH3)6]2+ > [Ni(NO2)6]4–
(l about 700 nm) (about 500 nm) (< 500 nm)

Question. (a) What is the basis of formation of the spectrochemical series?
(b) Draw the structures of geometrical isomers of the following coordination complexes :
[Co(NH3)3Cl3] and [CoCl2(en)2]+
(en = ethylenediamine and atomic number of Co is 27)
Answer. 
(a) The arrangement of ligands in order of their increasing field strength i.e. increasing crystal field splitting energy (CFSE) value is called spectrochemical series.
(b) (i) The facial and meridional isomers of [Co(NH3)3Cl3] may be represented as

Coordination Compounds Class 12 Chemistry Important Questions

Question. Write the IUPAC name of the complex [Cr(NH3)4Cl2]+. What type of isomerism does it exhibit?
Answer. 
Tetraamminedichloridochromium(III)ion.
It exhibits geometrical isomerism.

Coordination Compounds Class 12 Chemistry Important Questions

Question. Draw the structures of optical isomers of each of the following complex ions :
[Cr(C2O4)]3–,[PtCl2(en)2]2+, [Cr(NH3)2Cl2(en)]+
Answer. 
[Cr(C2O4)]3–:

Coordination Compounds Class 12 Chemistry Important Questions
Coordination Compounds Class 12 Chemistry Important Questions

Coordination Compounds Class 12 Chemistry Important Questions