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Important Questions for Class 12 Chemistry Chapter 9 cover linkage isomerism and coordination isomerism, coordination compounds stability. The article also includes wide-ranging questions on different types of isomerism, IUPAC, Ligands, Chelation, etc.
Coordination Compound contains complicated ions and a core metal atom or ion. These are surrounded by opposite and neutrally charged ions or molecules that are linked by several numbers of these ions or neutral molecules to form coordinate bonds. As catalysts, coordination compounds play a major role in altering the rate of chemical reactions. The production of polyethylene and polypropylene depends on certain complex metal catalysts.
The video below explains this:
Isomerism in Coordination Compounds Detailed Video Explanation:
Very Short Answer Type Questions (1 Mark Question)
Ques: Give an example of coordination isomerism. (CBSE Delhi, 2010)
Ans: [Co (NH3)6] [Cr (CN)6] and [Cr (NH3)6] [Co(CN)6]
Ques: Give an example of ionisation isomerism. (CBSE Delhi, 2010)
Ans [Pt (NH3)5 (Br)3] SO4 and [Co (NH3)5 (SO4)] Br.
Ques: Which of the following is a more stable complex and why? [CO(NH3)6]3+ and [Co(en)3]3+ (CBSE Delhi and AI 2014)
Ans: [Co(en)3]3+ because bidentate ligand (ethylenediamine) that forms chelate is more stable.
Ques: Write the IUPAC name of the complex [Cr(NH3)4Cl2]. What type of Isomerism does it exhibit? (CBSE Delhi, 2014)
Ans: Tetraamminedichlorochromium(III) ion. It displays cis and trans isomerism. Cis form then shows optical isomerism.
Ques: Indicate the types of isomerism exhibited by the complex [Co(NH3)5 (NO2)] (NO3)2. (At. no. Co = 27). (CBSE AI 2012)
Ans: It indicates ionisation isomerism and linkage isomerism.
Ques: What type of bonding helps in stabilising the a-helix structure of proteins? (CBSE Delhi, 2013)
Ans: A-helix formation -» Intramolecular hydrogen bonding.
Ques: Give two examples of ligands that form coordination compounds useful in analytical chemistry. (CBSE AI 2013)
Ans: Examples: (i) EDTA (Ethylene diamine tetra-acetic acid);
(ii) Dimethyl glyoxime (DMG)
Ques: What is the IUPAC name of the complex [Ni(NH3)6]Cl2? (CBSE AI 2013)
Ans: [Ni(NH3)6]Cl2
IUPAC name: Hexaamminenickel (II) chloride.
Ques: (i) Write down the IUPAC name of the following complex [Co(NH3)5(N02)] (N03)2
(ii) Write the formula for the following complex: Potassium tetracyanonickelate (II) (CBSE 2015)
Ans: Pentaamminenitrito-N-cobalt(III) nitrate
K2[Ni(CN)4]
Short Answer Type Questions (2 Marks)
Ques: What is coordination isomerism? Give one example. (CBSE Delhi, 2014)
Ans: When both cation and anion are complexes and there is an exchange of the ligands is called coordination isomerism. Examples: [CO(NH3)6] [Cr (CN)6] and [Cr (NH3)6] [Co (CN)6].
Ques: Write IUPAC name of the complex [Co(en)2(H20)(CN)]2+
OR
Using IUPAC norms, write the formula of Ammonium tetrafluoride cobaltates (II). (CBSE AI 2019)
Ans: Aquacyanidobis (ethane-1,2-diamine) cobalt (III) ion
OR
(NH4)2[Co F4]
Ques: Write the IUPAC name of the complex K3[Cr(C204)3].
OR
Using IUPAC norms write the formula of Hexaamminecobalt (III) sulphate. (CBSE AI 2019)
Ans: Potassium trioxalatochromate(III)
OR
[Co(NH3)6]2 (S04)3
Ques: Write IUPAC name of the complex [Co(en)2CI2]
OR
Using IUPAC norms, write the formula of Sodium tetrachloridonickelate(II). (CBSE AI 2019)
Ans: Dichloridobis (ethylenediamine) cobalt(III) ion.
OR
Na2[NlCl4]
Ques: Give an example of linkage isomerism. (CBSE Delhi, 2010)
Ans: When two or more atom in an ambidentate ligand is linked with a central metal ion to form two types of complexes, then the formed isomers are known as linkage isomers and the phenomenon called linkage isomerism.
Examples: [Cr (H2O)5(NCS)]2+ Pentaaquathiocyanate chromium (III) ion, [Cr (H2O)5(NCS)]2+ Pentaaquaisothiocyanate chromium (III) ion.
Ques: Using IUPAC norms write the formulae for the following:
(a) Potassium trioxalatoaluminate (III)
(b) Dichloridobis(ethane-l, 2-diamine) cobalt (III) (All India 2017)
Ans: (a) K3[Al(C2O4)3]
(b) [Co(Cl)2(en)2]+
Also read:
Long Answer Type Questions (3 Marks)
Ques: Write the hybridisation and magnetic character of the following complexes:
(i) [Fe(H2O)6]2+
(ii) [Fe(CO)5] (Atomic no. of Fe = 26) (CBSE Delhi, 2019)
Ans: [Fe(H20)6]2+
Hybridisation: sp3d2
Magnetic character: Paramagnetic due to 4 unpaired electrons.
Fe(C0)5
Hybridisation: dsp3
Magnetic character: It is diamagnetic.
Ques: Write the types of isomerism exhibited by the following complexes:
(i) [Co(NH3)5Cl]S04
Ans: Ionisation isomerism
(ii) [Co(en)3]3+
Ans: Optical isomerism
(iii) [Co(NH3)6] [Cr(CN)6] (CBSE Delhi, 2013)
Ans: Coordination isomerism
Ques: When a co-ordination compound CrCl3.6H2O is mixed with AgNO3, 2 moles of AgCl are precipitated per mole of the compound. Write
(i) Structural formula of the complex.
(ii) IUPAC name of the complex. (CBSE Delhi, 2016)
Ans: (i) The complex formed on mixing a coordination compound CrCl3.6H2O with AgNO3 is as follows
CrCl3.6H2O + AgNO3 → [Cr(H2O5)Cl]Cl2. H2O
(ii) Pentaaquachloridochromium (III) chloride monohydrate
Ques: (i) Write down the IUPAC name of the following complex:
[CO(NH3)5Cl]2+
(ii) Write the formula for the following complex: Potassium tetrachloridonickelate (II) (CBSE AI 2015)
Ans: (i) [CO(NH3)5Cl]2+
IUPAC name: Pentaammine chlorido cobalt (III) ion
(ii) Formula of the complex potassium tetrachloridonickelate (II) K2[NiCl4]
Ques: When a coordination compound NiCl2.6H20 is mixed with AgNO3, 2 moles of AgCI are precipitated per mole of the compound. Write:
(i) Structural formula of the complex
(ii) IUPAC name of the complex (CBSE 2016)
Ans: For one mole of the compound, 2 moles of AgCI are precipitated with AgNO3, which indicates 2 ionisable Cl” ions in the complex.
- Structural formula: [Ni (H20)6]Cl2
- IUPAC name: Hexaaquanickel (II) chloride
Very Long Answer Type Questions. (5 Marks)
Ques: Predict the number of unpaired electrons in the square planar [Pt(CN)4]2- ion.
OR
Amongst [Fe(C204)3]3- and [Fe(NH3)6]3+ which is more stable and why? (CBSE 2019C)
Ans: The Pt (II) ion has 5d8 electronic configuration. Dsp2 hybridisation is involved in the square planar geometry. One empty d-orbital is needed for hybridisation. Therefore, the pairing of electrons takes place in the remaining d-orbitals. Hence, there are no unpaired electrons in [Pt(CN)4]2- ion and it is diamagnetic.
OR
[Fe(C204)3]3- is more stable because it is a chelate. C2042- is a didentate ligand.
Chelation occurs when two or more donor atoms of a didentate or a polydentate ligand bind the same central metal or atom or ion forming a ring structure. As a result, a ring structure complex and the ligand coordinates through two or more donor groups are called chelating ligand. Examples: carbonate ion, oxalate ion (ox2-), ethylenediamine (en), ortho-phenanthroline (ph) and ethylenediaminetetraacetate ion (EDTA). Chelate ligands complex is more stable than ordinary complexes in which the ligand acts as monodentate. This is called a chelate effect.
Ques: Write IUPAC name of the complex [Pt(en)2Cl2]. Draw structures of geometrical isomers for this complex.
OR
Using IUPAC norms write the formulae for the following:
(i) Hexaamminecobalt (III) sulphate
(ii) Potassium trioxalatochromate (III) (CBSE Delhi, 2019)
Ans: Dichlorido bis(ethane-1,2-diamine) platinum (II)
OR
(i) [CO(NH3)6]2(S04)3
(ii) K3[Cr(ox)]3
Ques: Out of [COF6]3- and [Co(en)3]3+, which one complex is
(i) paramagnetic
(ii) more stable
(iii) inner orbital complex
(iv) high spin complex (Atomic no. of Co = 27) (CBSE Delhi, 2019)
Ans: [CoF6]3- is paramagnetic due to the presence of 4 unpaired electrons.
[Co(en)3]3+ is more stable because of chelation.
[Co(en)3]3+ forms an inner orbital complex involving d2sp3 hybridisation.
[COF6]3- forms a high spin complex (sp3d2 hybridisation).
Ques: Describe the shape and magnetic behaviour of the following complexes:
(i) [CO(NH3)6]3+
(ii) [Ni(CN)4]2- (At. No. Co = 27, Ni = 28) (CBSE DELHI 2010)
Ans: (i) [CO(NH3)6]3+:
Orbitals of CO3+ ion
Hybridization: d2sp3 Shape: Octahedral Magnetic behaviour: Diamagnetic (absence of unpaired electrons)
(ii) [Ni(CN)4]2-
Ques: Write IUPAC name of the complex [Cr(NH3)4Cl2]+. Draw structures of geometrical isomers for this complex.
OR
Using IUPAC norms write the formulae for the following:
(i) Pentaamminenitrito-O-cobalt(III) chloride
(ii) Potassium tetracyanidonickelate(II) (CBSE Delhi, 2019)
Ans: IUPAC name: Tetramminedichloridochromi um(III) ion.
OR
(i) [CO(NH3)5(ONO)]Cl2
(ii) K2[Ni(CN)4]
Ques: Draw one of the geometrical isomers of the complex [Pt(en)2Cl2]2+ which is optically inactive. Also, write the name of this entity according to the IUPAC nomenclature.
OR
Discuss the bonding in the coordination entity [Co(NH3)6 ]3+ on the basis of valence bond theory. Also, comment on the geometry and spin of the given entity. (Atomic no. of Co= 27). (CBSE Sample Paper 2019)
Ans: IUPAC Name of the entity:
Dichloridobis (ethane – 1,2-diamine) platinum(IV) ion
Ques: Write the name, stereochemistry and magnetic behaviour of the following:
(i) K4[Mn(CN)6]
(ii) [Co(NH3)2 C1]Cl2
(iii) K2[Ni(CN)4] (CBSE Delhi, 2011)
Ans:
| Complex | Name | Stereochemistry | Magnetic behaviour |
|---|---|---|---|
| (i) K4[Mn(CN)6] | Potassium hexacyanomanganate (I) | Octahedral | Paramagnetic |
| (ii) [Co(NH3)5Cl]Cl2 | Pentaamminechtorido cobalt (III) chloride | Octahedral | Diamagnetic |
| (iii) K2[Ni(CN)4) | Potassium tetracyanonicketate (II) | Square planar | Diamagnetic |
Ques: For the complex [Fe(en)2Cl2]Cl identify the following:
(i) Oxidation number of iron
Ans: III.
(ii) Hybrid orbitals and shape of the complex
Ans: d2sp3 hybridisation, octahedral
(iii) Magnetic behaviour of the complex
Ans: Paramagnetic due to one unpaired electron
(iv) Number of its geometric isomers
Ans: Two
(v) Whether there may be optical isomer also
Ans: One optical, isomer of cls-geometrical isomer.
(vi) Name the complex. (CBSE 2011)
Ans: Dichloridobis(ethylenediamine) iron (III) chloride.
Ques: 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+ ¡on is bound to two water molecules and two oxalate ions. Write the name and magnetic behaviour of each of the above coordination entitles. (At. nos. CO = 27, Ni = 28) (CBSE 2012)
Ans: (i) [Co(NH3) (Cl) (en)2]2+ Amminechtoriðo bls-(ethane -1, 2-diamine) cobalt (III) ion Co(27)
Since there are no unpaired electrons, the complex is diamagnetic.
(ii) [Ni(H2O)2 (C2O4)2]2- Diaquadioxatatonickelate (II) ion Ni(28)
The complex has two unpaired electrons, therefore, it will be paramagnetic.
Ques: 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) (CBSE Delhi, 2009)
Ans: (i) [COF4]2: Tetrafluorido cobalt (III) ion
Coordination number = 4 Shape = Tetrahedral Hybridisation = sp3
Ques: State a reason for each of the following situations:
(i) CO2+ is easily oxidised to CO3+ in presence of a strong ligand.
Ans: The configuration of CO2+ is t2g6 eg1 and for CO3+, it is t2g6. The crystal field stabilisation energy is more than compensated for in the third ionisation enthalpy. Therefore, CO2+ is easily oxidised to CO3+ in the presence of a strong ligand.
(ii) CO is a stronger complexing reagent than NH3.
Ans: CO is a stronger complexing ligand than NH3 because it contains both σ and π characters and can also form a back bond (M → CO). Therefore, CO forms a stronger bond with the metal. It is also called a strong field ligand.
(iii) The molecular shape of Ni(CO)4 is not the same as that of [Ni(CN)4]2-. (CBSE Delhi, 2011)
Ans: The molecular shape of [Ni(C0)4] is tetrahedral because this complex nickel involves sp3 hybridisation. In [Ni(CN)4]2-, nickel involves dsp2 and its square planer in shape.
Ques: Write the IUPAC names of the following compounds:
(i) [Cr(NH3)3Cl3]
Ans: Triamminetrichloridochromium (III)
(ii) K3[Fe(CN)6]
Ans: Potassium hexacyanoferrate (III)
(iii) [CoBr2(en)2]+, (en = ethylenediamine) (CBSE Delhi, 2013)
Answer: Dibromidobis(ethylenediamine) cobalt (III) ion
Ques: (a) Give one chemical test as evidence to show that [Co(NH3)5Cl] S04 and [Co(NH3)55(S04)]Cl are ionisation isomers.
Ans: When [Co(NH3)5(S04)]Cl is mixed with silver nitrate solution, a white precipitate of AgCl is formed. But [Co(NH3)5Cl]S04 does not give white ppt with AgN03 solution.
[Co(NH3)5S03 ]Cl+AgN03 (Ag) → AgCl White ppt
[Co(NH3)5 Cl]S04 + AgN03 (Ag) → No white ppt
(b) [NiCl4]2- is paramagnetic while [Ni(C0)4] is diamagnetic though both are tetrahedral. Why? (Atomic no. of Ni = 28)
Ans: In [NiCl4]2-, the oxidation state of nickel is +2 and it has the electronic configuration: 3d8
Cl– ion is a weak field ligand and it pairs the electrons. Since it has two unpaired electrons, it is paramagnetic and undergoes sp3 hybridisation to form a tetrahedral structure.
In Ni (CO)4, the oxidation state of nickel is 0 and it has the electronic configuration: 3d8 4s2. CO is a strong field ligand.
Since it has no unpaired electron, it is diamagnetic and undergoes sp3 hybridisation, resulting in the tetrahedral geometry of the complex,
(c) Write the electronic configuration of Fe(III) on the basis of crystal field theory when it forms an octahedral complex in the presence of (i) strong field ligand, and (ii) weak field ligand. (Atomic no. of Fe = 26) (CBSE AI 2019)
Ans: Fe (III): 3d5
(i) Strong field ligand: t2g5 eg0
(ii) Weak field ligand: t2g3 eg2
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