What is a soft soap?
Chemical substances which concentrates at the surface of the solution or interfaces, from surface films, reduces surface tension of the solution and help in removing dirt and dust by emulsifying grease are called surfactants i.e., soap and detergents. Soaps are sodium or potassium salts of long chain fatty acids such as palmitic acid $\left(\mathrm{C}_{15} \mathrm{H}_{31} \mathrm{COOH}\right)$, stearic acid $\left(\mathrm{C}_{17} \mathrm{H}_3 \mathrm{COOH}\right)$ and linolic acid $\left(\mathrm{C}_{17} \mathrm{H}_{31} \mathrm{COOH}\right)$ Potassium salts of fatty acids such as palmitic acid, stearic acid and oleic acid are called soft soap.
Generally, potassium soap are soft to the skin so, they are named as soft soap.
If soap has high alkali content it irritates skin. How can the amount of excess alkali be determined? What can be the source of excess alkali?
A solution of soap is titrated with standard hydrochloric acid. It is an acid-base titration. In this titration, phenolphthalein is used as an indicator. During the preparation of soap, fat (i.e., glyceryl ester of fatty acid) is heated with aqueous sodium hydroxide
Thus, the source of this excess alkali (which irritates skin) is the alkali left unused when the soap is prepared by hydrolysis of fat.
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.
