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What change will you observe if you test soap with litmus paper (red and blue)?

Last updated date: 20th Jun 2024
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Hint: Often in day to day life we need to identify whether the given compound is acid or base but you can’t differentiate by tasting it because that may be hazardous. That’s why we need specific substances that behave differently in acid and base. They are often called as indicators. Common indicators are litmus paper, phenolphthalein, methyl orange, turmeric etc.

Complete step by step solution:
Acid: it is a compound that gives ${{H}^{+}}$ ion in water and sour in taste.
Base: it is a compound that gives $O{{H}^{-}}$ ion in water and bitter in taste.

- Litmus paper is made by treating the paper with natural dyes from lichens.
- Litmus paper is either red or blue. In the basic solution red litmus paper turns blue and in acidic solution blue litmus paper turns into red.
- Soap is a sodium salt of naturally occurring fatty acids. It is produced by a saponification or basic hydrolysis reaction of a fat or oil. Currently, sodium carbonate or sodium hydroxide is used to neutralize the fatty acid and convert it to the salt.

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\[{{C}_{11}}{{H}_{23}}CO{{O}^{-}}N{{a}^{+}}\] (Sodium laurate), ${{C}_{17}}{{H}_{35}}CO{{O}^{-}}N{{a}^{+}}$ (Sodium stearate), $C{}_{15}{{H}_{31}}CO{{O}^{-}}N{{a}^{+}}$ (sodium palmitate) etc. are some common examples of soaps.
- When we will put a drop of soap solution on a blue litmus paper, no change in its color will be observed.
- When we put a drop of soap solution on a red litmus paper, color change will be observed and red litmus paper will turn into blue.
- It gives us the conclusion that soap solutions are alkaline in nature.

Let’s discuss why it is alkaline in nature?
As you know that fatty acids are weak acids and sodium hydroxide is a strong base so the salt that is forming over here will be the salt of weak acid and strong base and salt of weak acid and strong base are basic in nature. Therefore the solution of soaps will be alkaline in nature.

Additional Information:
Following are some of the major types of soaps
- Kitchen Soap: It is a type of soap intended for use in the kitchen mainly to serve the purpose of dish-washing.
- Laundry Soap: It is effective in cleaning solid particles, grease and organic compounds in clothes. It can be quite convenient to wash clothes during travels because it is easy to carry.
- Medicated Soap: It is a type of soap with added antiseptics and disinfectants to kill bacteria.
Beauty Soap: It features fragrance and ingredients for different skin types. They can feature special oil blends or glycerin.

Note: Transparent soap is simply hot process soap made by dissolving soaps in ethanol and evaporating the excess solvent. Here ethanol is not making it transparent but at the time of preparation it actually dissolves the soap into clear liquid. In transparent soaps glycerin soap is a great option for people with sensitive skin.