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WBJEE: Study Notes & Important Questions for Coordination Compounds

Jan 23, 2018 17:17 IST
    WBJEE 2018: Coordination Compounds
    WBJEE 2018: Coordination Compounds

    West Bengal Joint Entrance Examination (WBJEE) is a state level common entrance test organized by West Bengal Joint Entrance Examinations Board for admission to the Undergraduate Level Engineering and Medical Courses through a common entrance test in the State of West Bengal.

    Students can easily get a descent rank in WBJEE as the difficultly level is not tough like other engineering entrance exams like JEE and UPSEE.

    As competition is increasing day by day, students will have to do smart study. They should try to cover maximum syllabus of all the subjects just before few days of the examination. But it will not be possible if they try to read books.

    Students should concentrate only on the revision notes or study notes. It will help them to cover all important topics in a very less time. As a result they can save their precious time and cover maximum syllabus in minimum time.

    WBJEE: Important Questions and Preparation Tips for Alcohol

    The chapter ‘Coordination Compounds’ is a very important part of Inorganic Chemistry in the syllabus of WBJEE 2018.  Students always get about 1-2 questions from this chapter in the examination.

    After the detailed analysis of previous years’ papers and the latest syllabus of WBJEE, Subjects Experts bring to you the study notes of chapter Coordination Compounds.

    Students can learn about the following topics here:

    1. Werner coordination compound theory,

    2. Important terms in coordination compound,

    3. Nomenclature of coordination compound,

    4. Valence bond theory and

    5. Crystal field theory

    Important Concepts:

    The main postulates of Werner coordination compounds theory are as under:

    (i) Metals show two types of linkages in coordination compounds - primary and secondary.

    (ii) The primary linkages are normally ionisable.

    (iii) The secondary linkages are non ionisable.

    (iv) The ions/groups bound by the secondary linkages to the metal have characteristic spatial arrangements called polyhedra corresponding to different coordination numbers.

    (v) Octahedral, tetrahedral and square planar geometrical shapes are more common in coordination compounds of transition metals.

    Important Terms In Coordination Compounds

    (i) Coordination entity: An assembly that consists of central metal atom or ion to which is attached a surrounding array of other groups of atoms.

    (ii) Central atom/ion: The atom/ion to which a fixed number of ions/groups are bound in a definite geometrical arrangement around it.

    (iii) Ligands: The ions or molecules that bind to the central atom/ion in the coordination entity are called ligands.

    (iv) Coordination number: It is defined as the number of ligands that immediately surrounds central atom.

    (v) Coordination sphere: The square bracket in which the central atom/ion and the ligands attached are enclosed is called coordination sphere.

    All the terms can be shown with the help of diagram as below:

    WBJEE Coordination Compounds

    WBJEE Coordination Compounds

    WBJEE: Important Questions and Preparation Tips –Periodic Classification & Periodicity in Properties

    Some solved questions are given below:

    Question 1:

    Optical isomerism is exhibited by (ox = oxalate anion; en = ethylenediamine)

    (a) cis-[CrCl2(ox)2]3–

    (b) [Co(en)3]3+

    (c) trans-[CrCl2(ox)2]3–

    (d) [Co(ox)(en)2]+

    Solution 1:

    Optical isomers are those molecules which differ three-dimensionally by the placement of substituent around one or more atoms in a molecule. Trans-[CrCl2(ox)2]3– has plane of symmetry.

    Hence, the correct options are (a), (b) and (d).

    Question 2:

    Which of the following species is not expected to be a ligand?

    (a) NO                                                            

    (b) NH4+

    (c) NH2CH2CH2NH2                                        

    (d) CO

    Solution 2:

    Ligand must donate a pair of electron or loosely held electron pair to metal and form a M-L bond.

    e.g., NH2CH2CH2NH2, :CO

    Among NH4 does not have any pair of electron.

    Hence NH4 is not a ligand.

    Hence, the correct option is (b).

    Question 3:

    Due to the presence of ambidentate ligands coordination compounds show isomerism. Palladium complexes of the type [Pd(C6H5)2(SCN)2] and [Pd(C6H5)2(NCS)2] are

    (a) linkage isomers                                          

    (b) coordination isomers

    (c) ionisation isomers                                      

    (d) geometrical isomers

    Solution 3:

    The ligand(s) which has two different bonding sites are known as ambident ligands e.g., NCS,NO2 etc

    Here, NCS has two binding sites at N and S.

    Hence, NCS (thiocyanate) can bind to the metal ion in two ways

    M ← NCS or M → SNC

    Thus, coordination compounds containing NCS as a ligand can show linkage isomerism i.e.,[Pd(C6h5)2(SCN) and [Pd(C6H5)2(NCS)2]are linkage isomers.

    Hence, the correct option is (a).

    Question 4:

    Indicate the complex ion which shows geometrical isomerism.

    (a) [Cr(H2O)4Cl2]+          

    (b) [Pt(NH3)3 Cl]            

    (c) [Co(NH3)6]3+             

    (d) [Co(CN)5(NC)]3-

    Solution 4:

    [Cr(H2O)4Cl2]+shows geometrical isomerism because it is a MA4B2 type coordination compound Which contains two set of equivalent ligands, four H2O and 2 Cl.

    Hence the possible geometrical isomers are

    WBJEE Coordination Compounds Sol 4

    Hence, the correct option is (b).

    Question 5:

    The ionisation isomer of [Cr(H2O)4Cl(NO2 )]Cl is                                 

    (a) [Cr(H2O)4(O2N)]Cl2

    (b) [Cr(H2O)4Cl2](NO2)

    (c) [Cr(H2O)4Cl(ONO)]Cl

    (d) [Cr(H2O)4Cl2(NO2)]H2O

    Solution 5:

    Ionisation isomers are the complexes that produce different ions in solution, i.e. they have ions interchanged inside and outside the coordination sphere.

    [Cr(H2O)4Cl(NO2)]Cl and [Cr(H2O)4Cl2](NO2) have different ions inside and outside the coordinate sphere and they are isomers.

    Therefore, they are ionisation isomers.

    Hence, the correct option is (b).

    Question 6:

    As per IUPAC nomenclature, the name of the complex [Co (H2O)4(NH3 )2]C13 is 

    (a) tetraaquadiaminecobalt (III) chloride

    (b) tetraaquadiamminecobalt (III) chloride

    (c) diaminetetraaquacobalt (III) chloride

    (d) diamminetctraaquacobalt (III) chloride

    Solution 6:

    First of all, the compound has complex positive part [Co(H2O)4(NH3)2]3+ therefore, according to IUPAC conventions, positive part will be named first. Secondly, in writing name of complex, ligands are named first in alphabetical order, irrespective of its charge, hence "ammine" will be written prior to "aqua".

    NOTE In alphabetical order, original name of ligands are considered not the initials of prefixes. Also, special precaution should be taken in spelling name of NH3 ligand as it is ammine. Therefore, name of the complex is [Co(H2O)4(NH3)2]Cl3

    Diamminetetraaqua cobalt (III) chloride.

    Hence, the correct option is (d).

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    Conclusion:

    These notes will help students to get familiar with the difficulty level of the questions which can be asked in the coming examination. Students can refer these notes before the examination to save their precious time.

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