Chapter 9 Coordination Compounds

NCERT IN-TEXT QUESTIONS

Question 1.

Write the formulas of the following coordination compounds:

(a) tetraamminediaquacobalt (III) chloride

(b) potassium tetracyanonickelate (II)

(d) amminebromidochloridonitrito-N-platinate (II)

(e) dichlorobis (ethane-1, 2-diamine) platinum (TV) nitrate

(f) iron (III) hexacyanoferrate (II).

Answer:

Question 2.

Write the IUPAC names of the following coordination compounds:

Answer:

Hexaamminecobalt (III) chloride

Pentaamminechloridecobalt (III) chloride

Potassium hexacyanoferrate (III)

Potassiumtrioxalatoferrate(III)

Potassium tetrachloridopalladate (II)

Diamminechloride (methylamine) platinum (II) chloride

Question 3.

Give the types of isomerism exhibited by the following complexes and draw the structures of these isomers:

Question 4.

Question 5.

Question 6.

Question 7.

Question 8.

Question 9.

Question 10.

Question 11.

NCERT EXERCISE

Question 1.

Explain bonding in co-ordination compounds in terms of Werner’s postulates.

Answer:

Werner’s coordination theory: Alfred Werner gave his co-ordination theory in 1893. The important postulates of this theory are:

(i) All metals in atomic or ionic form exhibit two types of valencies in coordination compounds :

(a) Primary or principal or ionic valency (—–),

(b) Secondary or auxiliary or nonionic valency (—).

The primary valency is ionizable and it is shown by dotted lines. The secondary valency is non-ionizable and is shown by a continuous line.

(ii) Primary valency represents oxidation states of a metal atom or ion and secondary valency represents the co-ordination number of metal ion which is fixed for a particular atom.

(iv) Secondary valencies are directed towards a fixed position in space.

(v) Every element tends to satisfy both its primary and secondary valencies. For this purpose a negative ion may often act a dual behaviour i.e., it may satisfy primary as well as secondary valency (—–,-).

Question 2.

Question 3.

Explain with two examples each of the following:

coordination entity, ligand, coordination number, coordination polyhedron, homoleptic and heterolepic.

Answer:

Question 4.

What is meant by unidentate, didentate and ambidentate ligands ? Give two examples for each.

Answer:

Question 5.

Specify the oxidation numbers of metals in the following co-ordination entities :

Question 6.

Using IUPAC norms write the formulas for the following:

(i)Tetrahydroxozincate(Il)

(ii)Potassium tetrachloridopalladate (II)

(iii)Diamminedichlorido platinum (II)

(iv)Potassium tetracyanonickelate (II)

(v)Pentaamminenitrito-O-cobalt(III)

(vi)Ilexaamminccobalt (III) sulphate

(vii)Potassium tri(oxalato) chromate (III)

(yiii)Hexaammineplatinum (IV)

(ix)Tetrabromidocuprate(II)

(x) Pentaamminenitrito-N-cobalt (III)

Answer:

Question 7.

Using IUPAC norms write the systematic names of the following :

Answer:

(a) hexamminecobalt(III) chloride

(b) tetramminechloriodonitrito-N-cobalt(III) chloride

(d) diamminechlorido (methaneamine) platinum(II) chloride

(e) hexaaquamanganese(II) ion

(f) tetrachloriodonickelate(II) ion

(g) tris(ethane-l, 2-diammine) cobalt(III) ion

(h) hexaaquatitanium(III) ion

(i) tetracarbonylnickel (0).

Question 8.

List various types of isomerism possible for coordination compounds, giving an example of each.

Answer:

Question 9.

How many geometrical isomers are possible in the following coordination entities ?

Answer:

Question 10.

Draw the structures of optical isomers of :

Answer:

Question 11.

Draw all the isomers (geometrical and optical) of :

Answer:

Question 12.

Write all the geometrical isomers of [Pt(NH3)(Br)(Cl)(py)]. How many of these will exhibit optical isomerism ?

Answer:

There are three geometrical isomers.

Question 13.

Aqueous copper sulphate solution (blue in colour) gives (a) green precipitate with aqueous potassium fluoride and (b) a bright green solution with aqueous potassium chloride solutions. Explain these experimental results.

Answer:

Question 14.

Question 15.

Question 16.

Draw figure to show the splitting of d-orbitals in octahedral crystal field.

Answer:

Question 17.

What is spectrochemical series? Explain the difference between a weak field ligand and a strong field ligand.

Answer:

Spectrochemical series: The arrangement of ligands in order of their increasing field strengths i.e. increasing crystal field splitting energy (CFSE) values is called spectrochemical series, which is as follows: Difference between weak field ligand and a strong field ligand: The ligand with a small value of CFSE (∆0) are called weak field ligands whereas those with a large value of CFSE are called strong field ligands.

Question 18.

What is crystal field splitting energy ? How does the magnitude of ∆0 decide the actual configuration of d- orbitals in a coordination entity ?

Answer:

Question 19.

Question 20.

Question 23.

Question 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 :

Question 25.

What is meant by stability of a coordination compound in solution ? State the factors which govern stability of complexes.

Answer:

The stability of a complex in solution refers to the degree of association between the two species involved in the state of equilibrium. The magnitude of the (stability or formation) equilibrium constant for the association, quantitatively expresses the stability. Thus, if we have a reaction of the type :

then, the larger the stability constant, the higher is the proportion of ML4 that exists in the solution. Free metal ions rarely exist in the solution so that M will usually be surrounded by solvent molecules which will compete with the ligand molecules, L, and be successively replaced by them. For simplicity, we generally ignore these solvent molecules and write four stability constants as follows :

Factors affecting stability of complexes :

The smaller the size of the cation, the greater will be the stability of the complex e.g., Fe3+ forms a more stable complex than Fe2+.

The greater the charge on the central metal ion, the more stable will be the complex e.g., Pt4+ forms a more stable complex than Pt2+.

Stronger the ligand, more stable will be the complex formed e.g., CN forms more stable complex then NH3.

Question 26.

What is meant by chelate effect ? Give an example.

Answer:

When a ligand attaches to the metal ion in a manner that form’s a ring, then the metal-ligand association is found to be more stable. In other words, we can say that complexes containing chelate ring more stable than complexes without rings. This is known as the chelate effect.

Question 27.

Discuss briefly giving an example in each case the role of coordination compounds in:

(i) biological systems

(ii) medicinal chemistry

(iii) analytical chemistry and

(iv) extraction/ metallurgy of metals.

Answer:

(i) Role of coordination compounds in biological systems:

We know that photosynthesis is possible by the presence of chlorophyll pigment. This pigment is a coordination compound of magnesium. In the human biological system, several coordination compounds play important roles. For example, the oxygen – carrier of blood, i.e hemoglobin is a coordination compound of iron.

(ii) Role of coordination compounds in Medicinal chemistry: Certain coordination compounds of platinum (for example cis-platin) are used for inhibiting the growth of tumors.

(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. These colour changes are a result of the coordination compounds or complexes that the basic radicals form with different ligands.

(iv) Role of coordination compounds in interaction or metallurgy of metals: The process of extraction of some of the metals from their ores involves the formation of complexes. For example in an aqueous solution, gold combines with cyanide ions to form [Au (CN)2]. From this solution, gold is later extracted by the addition of Zn metal.

Question 28.

How many ions are produced from the complex Co(NH3)6Cl2 in solution?

(a) 6

(b) 4

(d) 2.

Answer: