Explain why some times foaming is seen in river water near the place where sewage water is poured after treatment?
Detergents have long hydrocarbon chains. If their hydrocarbon chain is highly branched, then bacteria cannot degrade this easily. Such detergents are non-biodegradable. Slow degradation of detergents leads to their accumulation.
These non-biodegradable detergents persist in water even after sewage treatment and cause foaming in rivers, ponds and their water get polluted. In order to overcome this issue branching of the hydrocarbon chain is controlled and kept to minimum.
Which category of the synthetic detergents is used in toothpaste?
Anionic detergents such as sodium lauryl sulphate, sodium dodecylbenzenesulphonate etc are used in toothpaste. They are responsible to clean the teeth and to provide a foam that helps to carry away the debris.
Further, sodium lauryl sulphates have significant antibacterial properties, and can penetrate as well as dissolve the plaque.
Hair shampoos belong to which class of synthetic detergent?
Hair shampoos are made up of cationic detergents. These are quarternary ammonium salts of amines with acetates, chlorides or bromides as anions, e.g., cetyltrimethyl ammonium bromide.
Dishwashing soaps are synthetic detergents. What is their chemical nature?
Dishwashing soaps are non-ionic detergents. It can be prepared by the reaction of stearic acid with polyethylene glycol.
$$\mathrm{\mathop {C{H_3} - {{(CH)}_{16}}COOH}\limits_{Stearic\,acid} + HO - {(C{H_2}C{H_2}O)_n} - \mathop {C{H_2}C{H_2}OH}\limits_{Polyethylene\,glycol} \buildrel { - {H_2}O} \over \longrightarrow} \mathrm{CH}_3-\left(\mathrm{CH}_2\right)_{16} \mathrm{COO}\left(\mathrm{CH}_2 \mathrm{CH}_2 \mathrm{O}\right)_n \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{OH}$$
Since, non-ionic detergents do not contain any ion in their constitution, it is neutral in nature.
Draw the diagram showing micelle formation by the following detergent. $$ \mathrm{CH}_3\left(\mathrm{CH}_2\right)_{10} \mathrm{CH}_2 \mathrm{OSO}_3 \mathrm{Na}$$
Sodium lauryl sulphate, $\mathrm{CH}_3\left(\mathrm{CH}_2\right)_{10} \mathrm{CH}_2 \mathrm{OSO}_3^{-}{ }^{+} \mathrm{Na}$ is an example of anionic detergent. When added to water, it dissociates as follows
$$\mathrm{C{H_3} - {(C{H_2})_{10}} - C{H_2}OSO_3^ - \mathop N\limits^ + a\buildrel { + {H_2}O} \over \longrightarrow C{H_3} - {(C{H_2})_{10}}C{H_2} - OSO_3^ - \mathop N\limits^ + a}$$
These anions are present on the surface with their $-\mathrm{OSO}_3^{-}$groups in water and hydrocarbon part staying away from it and remain at the surface.
At higher concentration, these anions are pulled into the bulk of the solution and form an aggregate of spherical shape with their hydrocarbon part pointing towards the centre and $\mathrm{OSO}_3^{-}$part outwards on the surface of the sphere.
An aggregate thus formed is known as micelle.
