Samacheer Class 10 Science - Carbon and its Compounds

(i) Propane is an acyclic saturated alkane. It is a straight-chain hydrocarbon with the molecular formula C3H8. Its structural formula is CH3-CH2-CH3, where three carbon atoms are linked by single bonds and each carbon atom is bonded to the required number of hydrogen atoms to satisfy its valency. (ii) Benzene is a cyclic aromatic hydrocarbon with the molecular formula C6H6. Its structure consists of a six-membered ring of carbon atoms with alternating single and double bonds, exhibiting resonance. (iii) Cyclobutane is an alicyclic saturated hydrocarbon with the molecular formula C4H8. It forms a four-membered ring of CH2 groups, where the carbon atoms are joined by single bonds. (iv) Furan is a heterocyclic aromatic compound with the molecular formula C4H4O. It has a five-membered ring containing four carbon atoms and one oxygen atom, with two double bonds within the ring, giving it aromatic character.

Some detergents cause water pollution because they contain branched hydrocarbon chains which are not easily biodegradable. These persistent detergents remain in water bodies, leading to the formation of persistent foam and a significant reduction in water quality. Furthermore, certain detergents contain phosphates, which act as nutrients for aquatic plants. An excessive amount of phosphates can lead to eutrophication, characterized by rapid growth of algae (algal blooms). When these algae die and decompose, they consume large amounts of dissolved oxygen in the water, creating hypoxic conditions that are harmful or fatal to fish and other aquatic life. To prevent this pollution, remedial measures include using biodegradable detergents with straight-chain hydrocarbon structures, opting for phosphate-free detergent formulations, using detergents only in the required quantities, treating wastewater effectively before its discharge into natural water bodies, and avoiding the release of untreated detergent-laden water into rivers and lakes.

To systematically arrive at the IUPAC name of the compound CH3-CH2-CH2-OH, we follow a series of steps. First, identify the longest carbon chain that contains the principal functional group. In this case, the longest carbon chain consists of three carbon atoms, so the root word is 'prop'. Second, determine the type of carbon-carbon bonds present in this chain. Since all bonds between carbon atoms are single bonds, the primary suffix is 'ane'. Third, identify the principal functional group. The compound contains a hydroxyl (-OH) group, indicating that it is an alcohol. Therefore, a secondary suffix is required. Fourth, number the carbon chain starting from the end that is closest to the principal functional group to give it the lowest possible locant number. In CH3-CH2-CH2-OH, numbering from the right gives the -OH group on carbon 1 (CH3-CH2-CH2-OH), while numbering from the left would place it on carbon 3. Thus, we number from the right: 3 2 1 CH3-CH2-CH2-OH. The -OH group is attached to carbon number 1. Finally, combine the root word, primary suffix, and secondary suffix, indicating the position of the functional group. The secondary suffix for an alcohol is '-ol', and its position is indicated by the locant number. Therefore, the IUPAC name is propan-1-ol.

The cleansing action of soap is based on its molecular structure and its ability to form structures called micelles. A soap molecule is amphipathic, meaning it has two distinct parts: a polar, ionic head (the carboxylate group, -COO- Na+) and a long, non-polar hydrocarbon tail. The polar head is hydrophilic, meaning it is attracted to water molecules. The non-polar tail is hydrophobic, meaning it is repelled by water but attracted to non-polar substances like oil and grease. When soap is dissolved in water containing dirt or grease, the hydrophobic tails of the soap molecules orient themselves towards the grease particles, while the hydrophilic heads remain in contact with the surrounding water. This arrangement causes the soap molecules to surround the grease particles, forming spherical clusters called micelles. The grease and dirt are trapped within the hydrophobic core of the micelle. The outer surface of the micelle, composed of the hydrophilic heads, allows it to be dispersed in water. When the water is agitated, these micelles, along with the trapped dirt and grease, are lifted from the surface and washed away, thus cleansing the fabric or surface.