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NCERT Solutions Class 12 Chemistry Chapter 5 - Coordination Compounds
NCERT Solutions to Class 12 Chemistry Chapter 5 (Coordination Compounds) are a key to students developing a strong conceptual basis for CBSE board exams and other competitive exams (like JEE Main, JEE Advanced and NEET). Theoretical foundations provided in this chapter will enable students to comprehend Complex Salts and Bonding in Metal Complexes. Understanding these concepts is very important to the students as these concepts lead to many of the systems that are based on this technology such as biological catalysts like Hemoglobin and Industrial applications such as Electroplating.
Students will be able to use the NCERT Solutions to Class 12 Chemistry Chapter 5 to predict complex structure and magnetic behaviour by using both the IUPAC Nomenclature System and Crystal Field Theory (CFT). Well documented NCERT Solutions allow students to build a basis for their fundamentals, practice important Structural Problems and as a result do well in Term Exams, Board Exams and National Level Competitive Examinations.
1.0Class 12 Chemistry Chapter 5 Coordination Compounds: Key Concepts
This chapter deals with the structure, naming, bonding, properties, and uses of coordination compounds. The main topics include:
- Werner’s Theory: Understand the difference between primary valency and secondary valency and how they explain the structure of coordination compounds.
- Basic Terms: Learn important terms such as coordination entity, central metal atom or ion, ligand, coordination number, coordination sphere, and oxidation state.
- Types of Ligands: Understand unidentate, didentate, and polydentate ligands and how they form bonds with the central metal ion.
- IUPAC Nomenclature: Learn the rules for naming coordination compounds, including the names of ligands, the central metal, and its oxidation state.
- Isomerism: Study structural isomerism, including linkage, ionisation, coordination, and solvate isomerism, along with stereoisomerism, including geometrical and optical isomerism.
- Valence Bond Theory (VBT): Learn how VBT explains the hybridisation, shape, and magnetic behaviour of coordination compounds. Important hybridisations include sp³, dsp², and d²sp³.
- Crystal Field Theory (CFT): Understand how d-orbitals split in octahedral and tetrahedral complexes and learn about crystal field splitting and crystal field stabilisation energy (CFSE).
- Bonding in Metal Carbonyls: Understand sigma (σ) and pi (π) bonding between metal atoms and carbon monoxide in metal carbonyls.
- Importance of Coordination Compounds: Study their applications in qualitative analysis, extraction of metals, and biological systems, including chlorophyll and Vitamin B₁₂.
2.0NCERT Solutions Class 12 Chemistry Chapter 5 Coordination Compounds) : Detailed Solutions
NTEXT QUESTIONS
- Write the formulas for the following coordination compounds : (i) Tetraamminediaquacobalt(III) chloride (ii) Potassiumtetracyanonickelate (II) (iii) Tris (ethane-1,2-diamine) chromium(III) chloride (iv) Amminebromideochloridonitrito-N platinate(II) (v) Dichloridobis(ethane-1,2-diamine) platinum(IV) nitrate (vi) Iron(III) hexacyanoferrate(II)
Sol. (i)
(ii) (iii) (iv) (v) (vi)
2. Write the IUPAC name of the following coordination compounds : (i) (ii) (iii) (iv) (v) (vi) Sol. (i) Hexamminecobalt (III) chloride (ii) Pentaamminechloridocobalt (III) chloride (iii) Potassiumhexacyanoferrate (III) (iv) Potassiumtrioxalatoferrate (III) (v) Potassiumtetrachloridopalladate (II) (vi) Diamminechlorido (methylamine) platinum (II) chloride
3. Indicate the types of isomerism exhibited by the following complexes and draw the structures for these isomers : (i) (ii) (iii) (iv)
Sol.
(i) Both geometrical (cis-, trans-) isomers for can exist. Also, optical isomers for cis-isomer exist.
(ii) Two-optical isomers for exist.
(iii) A pair of optical isomers
It can also show linkage isomerism and
It can also show ionization isomerism and
(iv) Geometrical (cis-, trans-) isomers of can exist.
4. Give evidence that and are ionization isomers. Sol. When ionization isomers are dissolved in water, they ionize to give different ions. These ions then react differently
White precipitate
White precipitate
5. Explain on the basis of valence bond theory that ion with square planar structure is diamagnetic and the ion with tetrahedral geometry is paramagnetic. Sol. Ni is in the +2 oxidation state i.e., in configuration. configuration :
In case of ion is a weak field ligand. Therefore, it does not lead to the pairing of unpaired 3d electrons. Therefore, it undergoes hybridization.
- 6. is paramagnetic while is diamagnetic though both are tetrahedral. Why? Sol. Though both and are tetrahedral, their magnetic characters are different. This is due to a difference in the nature of ligands. is a weak field ligand and it does not cause the pairing of unpaired electrons. Hence, is paramagnetic.
- Therefore, it causes the pairing of unpaired 3d electrons. Also, it causes the 4s electrons to shift to the 3d orbital, thereby giving rise to hybridization. Since no unpaired electrons are present in this case, is diamagnetic.
- 7. is strongly paramagnetic whereas is weakly paramagnetic. Explain. Sol. In both and , Fe exists in the +3 oxidation state i.e., in configuration.
- Since is a strong field ligand, it causes the pairing of unpaired electrons. Therefore, there is only one unpaired electron left in the -orbital.
- Therefore,
On the other hand, is a weak field ligand. Therefore, it cannot cause the pairing of electrons. This means that the number of unpaired electrons is 5 . Therefore,
Thus, it is evident that is strongly paramagnetic, while is weakly paramagnetic.
- Explain is an inner orbital complex whereas is an outer orbital complex.
Sol.
- Predict the number of unpaired electrons in the square planar ion. Sol. In this complex, Pt is in the +2 state. It forms a square planar structure. This means that it undergoes hybridization. Now, the electronic configuration of is .
-
being a strong field ligand causes the pairing of unpaired electrons. Hence, there are no unpaired electrons in .
- 10.The hexaquo manganese(II) ion contains five unpaired electrons, while the hexacyanoion contains only one unpaired electron. Explain using Crystal Field Theory.
- Calculate the overall complex dissociation equilibrium constant for the ion, given that for this complex is . Sol. The overall complex dissociation equilibrium constant is the reciprocal of the overall stability constant .
NCERT EXERCISE
- Explain the bonding in coordination compounds in terms of Werner's postulates ? Sol. Werner's postulates explain the bonding in coordination compounds as follows : (i) A metal exhibits two types of valencies namely, primary and secondary valencies. Primary valencies are satisfied by negative ions while secondary valencies are satisfied by both negative and neutral ions. (ii) A metal ion has a definite number of secondary valencies around the central atom. Also, these valencies project in a specific direction in the space assigned to the definite geometry of the coordination compound. (iii) Primary valencies are usually ionizable, while secondary valencies are non-ionizable
- solution mixed with solutions in 1 : 1 molar ratio gives the test of ion but solution mixed with aqueous ammonia in 1 : 4 molar ratio does not give the test of ion. Explain why ?
Sol.
Tetraamminocopper(II)sulphate
Both the compounds i.e., . and fall under the category of addition compounds with only one major difference i.e., the former is an example of a double salt, while the latter is a coordination compound.
- Explain with two examples each of the following: Coordination entity, ligand, coordination number, coordination polyhedron, homoleptic and heteroleptic.
Sol.
(i) Coordination entity : A coordination entity is an electrically charged radical or species carrying a positive or negative charge. In a coordination entity, the central atom or ion is surrounded by a suitable number of neutral molecules or negative ions (called ligands). For example :
⇒ Cationic complex
⇒ anionic complex
⇒ neutral complex (ii) Ligands : The neutral molecules or negatively charged ions that surround the metal atom in a coordination entity or a coordinal complex are known as ligands. For example etc. (iii) Coordination number : The total number of ligands (either neutral molecules or negative ions) that get attached to the central metal atom in the coordination sphere is called the coordination number of the central metal atom. It is also referred to as its ligancy.
For example :
(a) In the complex, , there as six chloride ions attached to Pt in the coordinate sphere. Therefore, the coordination number of Pt is 6 . (b) Similarly, in the complex , the coordination number of the central atom (Ni) is 4. (iv) Coordination polyhedron : Coordination polyhedrons about the central atom can be defined as the spatial arrangement of the ligands that are directly attached to the central metal ion in the coordination sphere.
For example :
(v) Homoleptic complexes : These are those complexes in which the metal ion is bound to only one kind of a donor group. For e.g. etc. (vi) Heteroleptic complexes : Heteroleptic complexes are those complexes where the central metal ion is bound to more than one type of a donor group. For e.g.
4. What is meant by unidentate, didentate and ambidentate ligands? Give two examples for each. Sol. A ligand may contain one or more unshared pairs of electrons which are called the donor sites of ligands. Now, depending on the number of these donor sites, ligands can be classified as follows : (a) Unidentate ligands : Ligands with only one donor sites are called unidentate ligands. •• For e.g., etc. (b) Didentate ligands : Ligands that have two donor sites are called bidentate ligands. For e.g.,
(c) Ambidentate ligands : Ligands that can attach themselves to the central metal atom through two different atoms are called ambidentate ligands. For example :
5. Specify the oxidation numbers of the metals in the following coordination entities: (i) (ii) (iii) (iv) (v)
Sol.
i) Let the oxidation number of Co be x. The charge on the complex is +2.
(ii) Let the oxidation number of Pt be x. The charge on the complex is -2.
(iii)
or
or
6. Using IUPAC norms write the formulas for the following :
(i) Tetrahydroxozincate (II)
(ii) Potassium tetrachloridopalladate (II)
(iii) Diamminedichloridoplatinum (II)
(iv) Potassium tetracyanonickelate (II)
(v) Pentaamminenitrito-O-cobalt (III)
(vi) Hexaamminecobalt (III) sulphate
(vii) Potassium tri(oxalato)chromate (III) (
viii) Hexaammineplatinum (IV)
(ix) Tetrabromidocuprate (II)
(x) Pentaamminenitrito-N-cobalt (III)
Sol:
(i)
(ii)
(iii)
(iv)
(v)
(vi)
(vii)
(viii)
(ix)
(x)
7. Using IUPAC norms write the systematic names of the following :
(i)
(ii)
(iii)
(iv)
(v)
(vi)
(vii)
(viii)
(ix)
Sol:
(i) Hexaamminecobalt (III) chloride
(ii) Diamminechlorido (methylamine) platinum (II) chloride
(iii) Hexaaquatitanium (III) ion
(iv) Tetraamminechloridonitrito-N-Cobalt(III) chloride
(v) Hexaaquamanganese (II) ion
(vi) Tetrachloridonickelate (II) ion
(vii) Hexaamminenickel (II) chloride
(viii) Tris (ethane-1, 2-diammine) cobalt (III) ion
(ix) Tetracarbonylnickel (0)
8. List various types of isomerism possible for coordination compounds, giving an example of each
Sol:
(a) Geometrical isomerism : This type of isomerism is common inheteroleptic complexes. It arises due to the different possible geometric arrangements of the ligands. For example :
(b) Optical isomerism : This type of isomerism arises in chiral molecules. Isomers are mirror images of each other and are non - superimposable.
(c) Linkage isomerism : This type of isomerism is found in complexes that contain ambidentate ligands. For example :
and
Yellow form Red form
(d) Coordination isomerism : This type of isomerism arises when the ligands are interchanged between cationic and anionic entities of different metal ions present in the complex. For example and
(e) Ionization isomerism : This type of isomerism arises when a counter ion replaces a ligand within the coordination sphere. For example and
(f) Solvate isomerism : Solvate isomers differ by whether or not the solvent molecule is directly bonded to the metal ion or merely present as a free solvent molecule in the crystal lattice.
Violet Blue-green
Dark green
9. How many geometrical isomers are possible in the following coordination entities ? (i) (ii)
Sol.
(i) For , no geometrical isomer is possible as it is a bidentate ligand.
(ii) Two geometrical isomers are possible.
10. Draw the structure of optical isomers of : (i) (ii) (iii) Sol. (i)
(ii)
(iii)
(Superimposable mirror images)
In total, three isomers are possible.
(ii)
Trans - isomers are optically inactive. Cis - isomers are optically active. (iii)
Cis - isomers are optically active.
- Write all the geometrical isomers of and how many of these will exhibit optical isomers ?
Sol.
From the above isomers, none will exhibit optical isomers. Tetrahedral complexes rarely show optical isomerization. They do so only in the presence of unsymmetrical chelating agents.
- Aqueous copper sulphate solution (blue in colour) gives : (i) A green precipitate with aqueous potassium fluoride, and (ii) A bright green solution with aqueous potassium chloride Explain these experimental results. Sol. Aqueous exists as . It is blue in colour due to the presence of ions. (i) When KF is added.
(ii) When KCl is added :
In both these cases, the weak field ligand water is replaced by the and ions.
14. What is the coordination entity formed when excess of aqueous KCN is added to an aqueous solution of copper sulphate? Why is it that no precipitate of copper sulphide is obtained when is passed through this solution? Sol.
i.e.,
Thus, the coordination entity formed in the process is . It is a very stable complex, which does not ionize to give ions when added to water. Hence, ions are not precipitated when is passed through the solution.
15. Discusss the nature of bonding in the following coordination entities on the basis of valence bond theory : (i) (ii) (iii) (iv)
Sol.
(i) Electronic configuration of is . Orbitals of ion :
(ii) In this complex, the oxidation state of Fe is +3. Orbitals of ion :
(iii) Cobalt exists in the +3 oxidation state in the given complex. Orbitals of ion :
Therefore, it cannot cause the pairing of the 3d orbital electrons.
Geometry = Octahedral
(iv) Cobalt exists in the +3 oxidation state. Orbitals of ion :
16. Draw figure to show the splitting of d orbitals in an octahedral crystal field. Sol.
17. What is spectrochemical series? Explain the difference between a weak field and a strong field ligand. Sol. A spectrochemical series is the arrangement of common ligands in the increasing order of their crystal - field splitting energy (CFSE) values. The ligands present on the R.H.S of the series are strong field ligands while that on the L.H.S are weak field ligands. Also, strong field ligands cause higher splitting in the d orbitals that weak field ligands.
- What is crystal field splitting energy ? How does the magnitude of decide the actual configuration of d-orbitals in a coordination entity? Sol. The degenerate d-orbitals (in a spherical field environment) split into two levels i.e., and in the presence of ligands. The splitting of the degenerate levels due to the presence of ligands is called the crystal - field splitting while the energy difference between the two levels ( and ) is called the crystal-field splitting energy. It is denoted by . After the orbitals have split, the filling of the electrons takes place. After 1 electron (each) has been filled in the three orbitals, the filling of the fourth electron takes place in two ways. It can enter the orbitals (giving rise to like electron configuration) or the pairing of the electrons can take place in the orbitals (giving rise to like electronic configuration). If the value of a ligand is less than the pairing energy (P), then the electrons enter the orbital. On the other hand, if the value of a ligand is more than the pairing energy (P), then the electrons enter the orbital.
- is paramagnetic while is diamagnetic. Explain why ?
Sol. In , Cr is in the +3 oxidation state i.e., configuration. Since there are three unpaired electrons in 3d-orbitals
Therefore, it undergoes hybridization and the electrons in the 3d orbitals remain unpaired. Hence, it is paramagnetic in nature.
In exists in the +2 oxidation state i.e., configuration.
20. A solution of is green but a solution of is colourless. Explain.
Sol. In is a weak field ligand. Therefore, there are unpaired elecrons in . In this complex, the 3d electrons from the lower energy level can be excited to the higher energy level i.e., the possibility of d-d transition is present. Hence, is coloured. In the electrons are all paired as is a strong field ligand. Therefore, d-d transition is not possible is . Hence, it is colourless.
21. and are of different colours in dilute solutions. Why ?
Sol. The colour of a particular coordination compound depends on the magnitude of the crystal-field splitting energy, . This CFSE in turn depends on the nature of the ligand. In case of and , the colour differs because there is a difference in the CFSE. Now is a strong field ligand having a higher CFSE value of compound to the CFSE value of water. This means that the absorption of energy for the intra d-d transition also differs. Hence the transmitted colour also differs.
- Discuss the nature of bonding in metal carbonyls.
Sol. The metal-carbon bonds in metals carbonyls have both and characters. A bond is formed when the carbonyl carbon donates a lone pair of electrons to the vacant orbital of the metal. A bond is formed by the donation of a pair of electrons from the filled metal d orbital into the vacent anti-bonding orbital (also known as back bonding of the carbonyl group). The bond strengthens the bond and vice-versa. Thus, a synergic effect is created due to this metal - ligand bonding. This synergic effect strengthens the bond between CO and the metal.
- Give the oxidation state, d-orbital occupation and coordination number of the central metal ion in the following complexes : (i) (ii) cis- (iii) (iv)
Sol.
(i) The central metal ion is . Its coordination number is 6 . The oxidation state can be given as :
The d orbitals occupation for is . (ii) cis- The central metal ion is . The coordination number is 6. The oxidation state can be given as :
The d orbitals occupation for is .
(iii) The central metal ion is . The coordination number is 4 . The oxidation state can be given as :
The d orbitals occupation for is .
(iv) The central metal ion is . The coordination number is 6 . The oxidation state can be given as :
The d orbitals occupation for is .
24. Write down the IUPAC name for each of the following complexes and indicate the oxidation state, electronic configuration and coordination number. Also give stereochemistry and magnetic moment of the complex :
(i) (ii) (iii) (iv) (v)
Sol.
(i) IUPAC Name : Potassiumdiaquadioxalatochromate (III) trihydrate. Oxidation state of chromium Electronic configuration : Coordination number Shape : octahedral
Stereochemistry :
Magnetic moment,
(ii) IUPAC name : Pentaamminechloridocobalt (III) chloride Oxidation state of ; Coordination number Shape : octahedral ; Electronic configuration : . Stereo chemistry :
Cis optically active Magnetic Moment = 0
(iii) IUPAC name : Trichloridotripyridinechromium (III) Oxidation state of chromium = +3 ; Electronic configuration for Coordination number = 6 ; Shape : octahedral. Stereochemistry :
Both isomers are optically active. Therefore, a total of 4 isomers exist. Magnetic moment,
(iv) IUPAC name : Caesiumtetrachloroferrate (III) Oxidation state of ; Electronic configuration Coordination number = 4 ; Shape : tetrahedral Stereochemistry : optically inactive Magnetic moment :
(v) IUPAC Name : Potassiumhexacyanomanganate (II) Oxidation state of manganese = +2; Electronic configuration: Coordination number = 6; Shape : octahedral Stereochemistry : optically inactive Magnetic moment,
- What is meant by stability of a coordination compound in solution? State the factors which govern stability of complexes. Sol. The stability of a complex in a solution refers to the degree of association between the two species involved in a state of equilibrium. Stability can be expressed quantitatively in terms of stability constant or formation constant.
For this reaction, the greater the value of the stability constant, the greater is the proportion of in the solution. Stability can be of two types : (a) Thermodynamic stability : The extent to which the complex will be formed or will be transformed into another species at the point of equilibrium is determined by thermodynamic stability. (b) Kinetic stability : This helps is determining the speed with which the transformation will occur to attain the state of equilibrium.
26. What is meant by the chelate effect? Give an example. Sol. When a ligand attaches to the metal ion in a manner that forms a ring, then the metal-ligand association is found to be more stable. In other words, we can say that complex containing chelate rings are more stable than complexes without rings. This is known as the chelate effect. For example :
27. Discuss briefly giving an example in each case the role of coordination compounds in : (i) biological system (ii) medicinal chemistry (iii) analytical chemistry (iv) extraction/metallurgy of metals
Sol.
(i) Role of coordination compounds in biological system : We know that photosynthesis is made possible by the presence of the chlorophyll pigment. This pigment is a coordination compound of magnesium. (ii) Role of coordination compounds in medicinal chemistry : Certain coordination compounds of platinum (for example, cis-platin) are used for inhibiting the growth of tumours. (iii) Role of coordination compounds in analytical chemistry : During salt analysis, a number of basic radicals are detected with the help of the colour changes they exhibit with different reagents. (iv) Role of coordination compounds in extraction or metallurgy of metals : From solution, gold is extracted by the addition of zinc metal.
28. How many ions are produced from the complex in solution ? (i) 6 (ii) 4 (iii) 3 (iv) 2 Sol. (iii) So, total 3 ions are produced.
29. Amongst the following ions which one has the highest magnetic moment value ? (i) (ii) (iii)
Sol.
(i) No. of unpaired electrons in Then,
(ii) No. of unpaired electrons in Then, (iii) No. of unpaired electrons in Hence, has the highest magnetic moment value.
30. The oxidation number of cobalt in is (i) +1 (ii) +3 (iii) -1 (iv) -3 Sol. So, oxidation number of cobalt is -1.
31. Amongst the following, the most stable complex is (i) (ii) (iii) (iv) Sol. We know that the stability of a complex increases by chelation. Therefore, the most stable complex is .
Thus, the amount of crystal-field splitting observed will be in the following order :
Hence, the wavelengths of absorption in the visible region will be in the order :
3.0NCERT Solutions Class 12 Chemistry | Chapter-wise Links
Get chapter-wise NCERT Solutions for Class 12 Chemistry with simple explanations of textbook questions, important concepts, formulas, and step-by-step solutions to numerical problems.
4.0Key Features of NCERT Solutions for Class 12 Chemistry Chapter 5
- Easy Naming of Coordination Compounds: Learn how to name coordination compounds correctly by identifying the ligands, central metal atom, coordination number, and oxidation state.
- VBT and CFT Explained Simply: Understand the basic ideas of Valence Bond Theory (VBT) and Crystal Field Theory (CFT) and learn why some coordination compounds are high-spin while others are low-spin.
- Clear Explanation of Isomerism: Learn about geometrical and optical isomerism in coordination compounds. Understand cis and trans forms as well as facial (fac) and meridional (mer) forms with simple examples.
- Magnetic Properties: Understand how the number of unpaired electrons determines the magnetic behaviour of coordination compounds. Learn how to calculate magnetic moment using the spin-only formula and express it in Bohr Magnetons (BM).
- Bonding and Shapes of Complexes: Study the bonding, coordination number, geometry, and shapes of important coordination compounds covered in Class 12 Chemistry Chapter 5.
- Important Terms and Reactions: Revise important concepts such as ligands, coordination entities, coordination number, oxidation state, chelate complexes, and stability of coordination compounds.