Case study (4 Marks)

Question 14 Marks

When anions and cations approach each other, the valence shell of anions are pulled towards the cation nucleus and thus, the shape of the anion is deformed. The phenomenon of deformation of anion by a cation is known as polarization and the ability of the cation to polarize the anion is called as polarizing power of cation. Due to polarization, sharing of electrons occurs between two ions to some extent and the bond shows some covalent character.
The magnitude of polarization depends upon a number of factors.

1. Out of $AlCl _3$ and $AlI _3$ which halides show maximum polarization? (1)
2. Out of $AlCl _3$ and $CaCl _2$ which one is more covalent in nature? (1)
3. The non-aqueous solvent like ether is added to the mixture of $LiCl , NaCl$ and KCl . Which will be extracted into the ether? (2)
OR
Out of $CaF _2$ and $CaI _2$ which one has a minimum melting point? (2)

Answer

1. $AlI _3$ halides show maximum polarization. The most covalent halide is $AlI _3$.
Since lesser, the electronegativity difference, the more covalent is the aluminum halide.
2. $AlCl _3$ is more covalent in nature.
3. LiCl will be extracted into the ether.
OR
$CaI _2$ has a minimum melting point.

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Question 24 Marks

The existing large number of organic compounds and their ever-increasing numbers has made it necessary to classify them on the basis of their structures. Organic compounds are broadly classified as open-chain compounds which are also called aliphatic compounds. Aliphatic compounds further classified as homocyclic and heterocyclic compounds. Aromatic compounds are special types of compounds. Alicyclic compounds, aromatic compounds may also have heteroatom in the ring. Such compounds are called heterocyclic aromatic compounds. Organic compounds can also be classified on the basis of functional groups, into families or homologous series. The members of a homologous series can be represented by general molecular formula and the successive members differ from each other in a molecular formula by a $- CH _2$ unit.

1. The successive members of a homologous series differ by which mass of amu? (1)
2. Does Pyridine, pyrrole, thiophene are all heteroaromatic compounds (1)
3. Difference between heterocyclic and homocyclic compound. (2)
OR
Is tetrahydrofuran is aromatic compounds? (2)

Answer

1. The successive members of a homologous series are differ by a $- CH _2$ group. The molecular mass of a $- CH _2$ group is 14 amu. Hence, each successive homologue of a homologous series differ by a mass of 14 amu .
2. Heterocyclic compounds are a major class of organic compounds characterized by the fact that some or all of the atoms in their molecules are joined in rings containing at least one atom of an element other than carbon and follow Huckels rule, the most common heterocycles are those having five or six-membered rings and containing hetero members of Nitrogen, oxygen, sulphur. Pyridine, pyrrole, thiophene are all heteroaromatic compounds
3. A cyclic compound in which the ring includes at least one atom of an element different from the rest is called heterocyclic compound. A homocyclic compound is a cyclic compound in which all the ring atoms are the same.
OR
Tetrahydrofuran is non-aromatic, due to absence of conjugation in $\pi$ electrons, and it does not follow Huckel's rule.

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Chemistry Case study (4 Marks)

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