This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Definitions – Coordination Compounds – 1”.
1. Which of the following is the coordination entity in K2[Zn(OH)4]?
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.
2. The central atom/ion of a coordination complex is also referred to as ________
a) Lewis acid
b) Lewis base
c) Bronsted-Lowry acid
d) Bronsted-Lowry base
Explanation: A Lewis acid is a species that can accept an electron pair. All cations are Lewis acids. Since the central atom of a coordination complex is metal and always accept electrons, it is a Lewis acid.
3. Identify the Lewis acid in K3[Al(C2O4)3].
Explanation: Aluminium ion is the Lewis acid as it can accept 3 electrons from the donor atom to form the complex [Al(C2O4)3]3-.
4. Which of the following is the central atom/ion in [CoCl(NH3)5]2+?
Explanation: The central ion in the given complex ion is cobalt as it accepts electrons to form a bond with Cl atom and ammonia molecules. Since the primary valence of Co in this compound is +3, the ion in Co3+.
5. Which of the following cannot be a ligand?
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.
6. How many donor atoms can EDTA4- ligand bind through?
Explanation: EDTA4- is a hexadentate ligand which can bind through two nitrogen and four oxygen atoms to a central metal ion, giving it a total of 2 + 4 = 6 donor atoms.
7. A protein can exist in a coordination entity as a ligand.
Explanation: A protein is a macromolecule that consists of atoms that may donate electrons to a metal ion to form a coordinate bond, and hence act as a ligand.
8. Which is the donor atom in the coordinate bond shown below?
d) Both N and O
Explanation: This is nitrito-N, formed by ambidentate ligand NO2- ion when it bonds through its N atom to the central metal ion. The other form is nitrito-O, which is formed when NO2- coordinates through the O1 atom.
9. The SCN– ion is a unidentate ligand.
Explanation: SCN– is an ambidentate ligand that can either bond through S atom or N atom to a central atom/ion. But, at a time there is only a single donor atom, either S or N, making it a unidentate ligand. For a fact, all ambidentate ligands are unidentate.
10. Coordination number is a characteristic of which of the following?
a) Central atom
c) Coordination entity
d) Coordination compound
Explanation: Coordination number is also known as the secondary valence of a central metal ion in a complex and is defined as the number of donor atoms it is directly bonded to. Hence, coordination number is a quantity associated with the metal ion.
11. What is the coordination number of chromium in K3[Cr(C2O4)3]?
Explanation: There are three oxalate groups attached to the central ion in the given compound, but since oxalate is a didentate ligand, there are a total of 6 donor atoms to which the metal is directly bonded. Thus, the CN of Cr in K3[Cr(C2O4)3] is 6.
12. Identify the coordination sphere in the compound K4[Fe(CN)6].
Explanation: The coordination sphere refers to the square bracket within which the central atom/ion and the groups attached to it are enclosed. This is a non-ionisable group as compared to the entity outside the bracket, which is ionisable and is known as the counter ion.
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