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The coordination compound comprises of a central atom and ligands, anions, and cations bonded with it. Here, the central atom is an atom to which neutral molecules and atoms are linked by a coordinate bond in a fixed geometrical arrangement, we also call it is as Lewis acid. And Ligands Donate lone pairs to the central atom and form a coordinate bond by linking. There are four types of ligands based on the bond they make with the central atom, covered in this chapter. These coordination compounds are also used as catalysts, also used for qualitative and quantitative analysis, extraction of metals, electroplating, photography, and as dyes. It also has biological importance. In this article, there are some MCQ-based questions and answers with explanations of the given topic. These questions are beneficial for students who are appearing for boards, JEE, NEET, or any other competitive exams.
Coordination Compounds
The video below explains this:
Isomerism in Coordination Compounds Detailed Video Explanation:
Ques 1: According to Werner’s theory of coordination compounds,
- Primary valency is ionizable
- Secondary valency is ionizable
- Primary and secondary valencies are ionizable
- Neither primary nor secondary valency is ionizable
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Ans: A.
Explanation: According to Werner’s theory of coordination compounds primary valency is ionizable and non-directional which is equivalent to the oxidation state of the central atom and it is satisfied by the negative charge. For example, primary valencies of Co and Pt in CoCl3 and PtCl4 respectively.
Ques 2: Among the following which are ambidentate ligands?
- SCN-
- NO3-
- NO2-
- C2O42-
- (i) and (iii)
- (i) and (iv)
- (ii) and (iii)
- (ii) and (iv)
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Ans: A. (i) and (iii) both are correct.
Explanation: SCN- and NO2- both are ambidentate ligands, here SCN- can bond by nitrogen and sulfur.
Similarly, NO2- can also bind to central atom by nitrogen as well as oxygen.
Ques 3: A coordination compound CrCl3.4H2O gives a white precipitate of AgCl with AgNO3. The molar conductance of the compound corresponds to two ions. The structural formula of the compound is
- [Cr(H2O)4Cl3]
- [Cr(H2O)3Cl3] H2O
- [Cr(H2O)4Cl2]Cl
- [Cr(H2O)4Cl] Cl2
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Ans: C
Explanation: Here in this question, it is given that the molar conductance of the compound corresponds to two ions and it gives white precipitate so, it is sure that one ion will be Cl- because it gives white precipitate on reaction with Ag. Hence the structure of the reaction will be,
[CrH2O)4Cl2Cl →[CrH2O)4Cl2++ Cl-
Ques 4: Identify the statement which is not correct.
- Coordination compounds are mainly known for transition metals.
- Coordination number and oxidation state of metal are the same.
- A ligand donates at least one electron pair to the metal atom to form a bond.
- [Co(NH3)4Cl2]+ is a heteroleptic complex.
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Ans: B
Explanation: Option B is an incorrect statement because it is not necessary that the oxidation number and coordination number of metal are the same. Because coordination number refers to the number of ligands that are bound to the central atom by coordination bond whereas oxidation state refers to a process where electrons are either gained or lost.
Ques 5: The coordination number and the oxidation state of the element E in the complex [E(en)2(C2O4)]NO2 (where (en) is ethylenediamine) are, respectively
- 6 and 3
- 6 and 2
- 4 and 2
- 4 and 3
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Ans: A
Explanation: Both the ligands present in the above complex [E(en)2(C2O4)]NO2 are bidentate ligands and hence coordination number of the above complex is 6 which means it is octahedral in nature. Therefore, using the formula oxidation state of E will be 3.
Ques 6: The charges x and y on the following ions are,
- [Co(NH3)2Cl4]X
- [Fe(CN)6]Y
(Oxidation state of Co is +3 and Fe is +2 in their respective complexes.)
- x = +1, y = -1
- x = -1, y = +3
- x = -1, y = -4
- x = -2, y = -3
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Ans: C
Explanation: In [Co(NH3)2Cl4]X it is given that oxidation state of Co is +3. Therefore, x=3+2×0+4×-1=-1. This implies that the charge of x is -1. Similarly, the oxidation state of Fe is given as +2, therefore, the value of y for the compound [Fe(CN)6]Y will be y=2+6×-1=-4.
Ques 7: Give a reason for the statement. ‘[Ni(CN)4]2- is diamagnetic while [NiCl4]2- is paramagnetic in nature.’
- In [NiCl4]2-, no unpaired electrons are present while in [Ni(CN)4]2- two unpaired electrons are present.
- In [Ni(CN)4]2-, no unpaired electrons are present while in [NiCl4]2- two unpaired electrons are present.
- [NiCl4]2- shows dsp2 hybridization hence it is paramagnetic.
- [Ni(CN)4]2- shows sp3 hybridization hence it is diamagnetic.
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Ans: B
Explanation: Since CN- is a very strong field ligand [Ni(CN)4]2- has zero unpaired electrons in its configuration and hence it is Diamagnetic in nature.
Whereas [NiCl4]2- is paramagnetic in nature because Cl- is a weak field ligand. Therefore [NiCl4]2- has two unpaired electrons in it.
Ques 8: Among the following compounds which are both paramagnetic and coloured?
- K2Cr2O7
- [Co(SO)4]
- (NH4)2[TiCl6]
- K3[Cu(CN)4]
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Ans: B
Explanation: In [Co(SO)4] Co has +2 oxidation state and there are unpaired electrons present in 3d- orbital, therefore, it shows paramagnetic nature. And due to the partially filled d-orbital, it is coloured.
Ques 9: CuSO4.5H2O is blue in colour while CuSO4 is colourless due to
- Presence of strong field ligand in CuSO4.5H2O.
- Absence of water (ligand), d – d transitions are not possible in CuSO4.
- Anhydrous CuSO4 undergoes d – d transitions due to crystal field splitting.
- Colour is lost due to the loss of unpaired electrons.
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Ans: B
Explanation: Due to the absence of ligand in anhydrous CuSO4 crystal field splitting does not take place and hence it is colourless. Whereas in CuSO4.5H2O, water act as a ligand and hence crystal field splitting takes place and results in d – d transition. Therefore, it is coloured.
Ques 10: If Pt in PtCl4.2HCl has a secondary valence of 6, how many mols of AgCl will 1 mol of the compound precipitate with excess AgNO3?
- 0
- 1
- 2
- 4
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Ans: A
Explanation: Given compound has secondary valency 6. Therefore, there will be 6 groups that will be linked to the Pt atom. But, we can see that it already has 6 groups linked to it and hence it can’t lose Cl atoms to form AgCl. Therefore, there won’t be any formation of AgCl.
Ques 11: What is the sum of the oxidation number of cobalt in [Co(H2O)(CN)(en)2]2+ and [CoBr2(en)2]+?
- +3
- +5
- +4
- +6
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Ans: D
Explanation: We know that in [Co(H2O)(CN)(en)2]2+ charge on H2O, CN and en group is 0,-1 and 0 respectively, also overall charge on the compound is +2. Therefore, let charge on Co be x.
Here,
+2=x+0-1+0
This implies, x = +3. Therefore, the charge on Co will be +3.
Similarly, charge on [CoBr2(en)2]+ is +1 and charge on Br is -1 and charge on en is 0. Let the charge on Co be y.
Here,
+1=y-2+0
Therefore, y = +3
Hence charge on Co will be +3.
Ques 12: Which of the following is the correct formulation of the entity according to IUPAC?
- (Co(CN)6)3-
- [Co(CN)6]3-
- [Co (CN)6]3-
- [Co(CN)6]-3
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Ans: B
Explanation: While writing the formula for any coordination entity, it should be written within square brackets without any spacing between ligands and the central atom. And while indicating charges number should be written before the sign.
Ques 13: A coordination complex [MX2L2], has a CN=4 and two unidentate ligands X and L. When the two L ligands are arranged opposite to each other in their geometry, it is called _______ isomer.
- Cis
- Trans
- Fac
- Mer
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Ans: A
Explanation: There are four CN, hence square planar will be the shape of complex and in tetrahedral shape isomerism cannot be observed.
Ques 14: Which of the following compounds has enantiomers?
- K3[Fe(CN)6]
- K3[Al(C2O4)3]
- K2[Zn(OH)4]
- K2[PdCl4]
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Ans: B
Explanation: K3[Al(C2O4)3] shows optical isomerism because of its octahedral structure and it is bounded with a didentate ligand oxalate. Whereas K3[Fe(CN)6], K2[Zn(OH)4], and K2[PdCl4] are compounds with unidentate ligands and CN of 6 (octahedral), 4, and 4 respectively
Ques 15: Which of the following compounds does not have a coordination isomer?
- [Ag(NH3)2][Ag(CN)2]
- [Cr(NH3)6][Co(CN)6]
- [Zn(NH3)4][PtCl4]
- [Cu(NH3)4][FeCl4]
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Ans: A
Explanation: Coordination symmetry occurs when there is a ligand exchange between cation and ionic complex ions containing different metal ions. In the compound [Ag(NH3)2][Ag(CN)2], both complexes contain the same metal ion Ag+, and are therefore not a coordination isomer.
Ques 16: Identify the correct naming for K3[Fe(CN)6].
- Tripotassium hexacyanidoferrate(III)
- Potassium hexacyanoferrate(III)
- Tripotassium hexacyanoferrate(III)
- Potassium hexacyanidoferrate(III)
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Ans: D
Explanation: While doing nomenclature of any compound the number of cations and anions are never denoted in its naming. Here, Potassium will be the name of the counter ion and tripotassium is not at all valid here. And the name of CN should end with –‘o’, cyanido being the correct naming.
Ques 17: Which of the following compounds has a meridional isomer?
- [Fe(NO)5Br]+
- [Al(CO)3(NO2)3]
- [K(NH)3)4(NO)2]+
- [Fe(H2O)2(CO)2(NO)2]3+
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Ans: B
Explanation: Fac-mer isomerism is only exhibited in octahedral coordination entities of the type [MA3B3] depending on the positions of the similar ligands.
Ques 18. A coordination complex’s core atom/ion is also known as ________
- Lewis base
- Lewis acid
- Bronsted-Lowry acid
- Bronsted-Lowry base
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Ans. B
Explanation: A Lewis acid is a species that has the ability to receive an electron pair. Lewis acids are all cations. It is a Lewis acid because the core atom of a coordination complex is metal and always accepts electrons.
Ques 19. Which of the following statements about coordination compounds’ bonding is incorrect?
- Crystal Field Theory
- VSEPR Theory
- Molecular Orbital Theory
- Valence Bond Theory
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Ans. B
Explanation: The VSEPR Theory uses electron pairs in atoms to explain the structure of particular molecules. The theories of VBT, CFT, LFT, and MOT explain the nature of bonding in coordination compounds.
Ques 20. Determine which of the following statements about VBT is incorrect.
- It does not explain the color of coordination compounds
- It can distinguish between strong and weak ligands
- It does not explain the kinetic stabilities of coordination compounds
- It is unreliable in the prediction of geometries of 4-coordinate complexes
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Ans. B
Explanation: One of VBT’s flaws is that it can’t tell the difference between weak and powerful ligands. Other options have their own set of drawbacks.
Ques 21. Which of the following statements about a charged coordinating entity is correct?
- The sign of the charge is written after the number
- The charge of the complex ion is written in parenthesis while naming the entity
- The charge is indicated as a subscript outside the square bracket on the right
- The charge on the complex ion is depicted along with the counter ion
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Ans. A
Explanation: The charge of a coordination entity is written outside the square brackets on the right side as a superscript with the number before the sign of charge, without the existence of the counter ion.
Ques 22. At 25°C, which of the following will not give a positive test for Cl– with AgNO3(aq)?
- COCl3.5NH3
- COCl3.6NH3
- COCl3.3NH3
- COCl3.4NH3
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Ans. C
Explanation: [CO(NH3)3Cl3) or COCl3.3NH3 does not have counter ions, so will not react with AgNO3(aq).
Ques 23. Pick out the correct statement with respect to [Mn(CN)J2-
- It is sp²d² hybridised, tetrahedral
- It is d²sp3 hybridised, octahedral
- It is dsp² hybridised, square planar
- It is sp3d² hybridised octahedral
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Ans. B
Explanation: d²sp3, inner orbital complex
Ques 24. Which of the following is the coordination entity in K2[Zn(OH)4]?
- K+
- Zn2+
- OH–
- [Zn(OH)4]2-
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Ans. D
Explanation: A coordination entity consists of a central metal atom bonded to a fixed number of atoms/molecules. Here, K+ is the counter ion, OH is the molecule bonded to the central atom which is Zn.
Ques 25. Which of the following cannot be a ligand?
- Ni2+
- Cl–
- H2O
- NH3
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Ans. A
Explanation: The ions/molecules bound to the central atom/ion is called a ligand. Ni2+ is a metal ion, and according to Werner the secondary valences can be satisfied only by neutral molecules or negative ions. Cl–, H2O and NH3 are all possible ligands.
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