Chemistry Class 12 NCERT Solutions: Chapter 9 Coordination Compounds Part 10

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Q: 25. What is meant by stability of a coordination compound in solution? State the factors which govern stability of complexes.


The stability of a complex in a solution refers to the degree of association between the two species involved in a state of equilibrium. Stability can be expressed quantitatively in terms of stability constant or formation constant.

Stability constant,

For this reaction, the greater the value of the stability constant, the greater is the proportion of in the solution.

Stability can be of two types:

(A) Thermodynamic Stability:

The extent to which the complex will be formed or will be transformed into another species at the point of equilibrium is determined by thermodynamic stability.

(B) Kinetic stability:

This helps in determining the speed with which the transformation will occur to attain the state of equilibrium

Factors that affect the stability of a complex are:

(A) Charge on the central metal ion:

The greater the charge on the central metal ion the greater is the stability of the complex.

2. Basic nature of the ligand: A more basic ligand will form a more stable complex.

2. Presence of chelate rings: Chelation increases the stability of complexes.

Q: 26. What is meant by the chelate effect? Give an example.


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

For example:

Q 26 Chelate Effect

Q 26 Chelate Effect

Q 26 Chelate Effect

Q: 27. Discuss briefly giving an example in each case the role of coordination compounds in:

(i) biological system

(ii) medicinal chemistry

(iii) analytical chemistry

(iv) extraction/metallurgy of metals


(i) Role of coordination compounds in biological systems:

We know that photosynthesis is made possible by the presence of the 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., haemoglobin, 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 tumours.

(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.

(iii) Role of coordination compounds in extraction or metallurgy of metals:

The process of extraction of some of the metals from their ores involves the formation of complexes. For example, in aqueous solution, gold combines with cyanide ions to form . From this solution, gold is later extracted by the addition of zinc metal.

Q: 28. How many ions are produced from the complex in solution?






(iii) The given complex can be written as .

Thus, along with two ions are produced.