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

\( \newcommand\) • • • • • • • • • • • • • • • Objectives • To perform and observe the results of a variety of chemical reactions. • To become familiar with the observable signs of chemical reactions. • To identify the products formed in chemical reactions and predict when a reaction will occur. • To write balanced equations for the reactions studied. • To use the results from the single replacement reactions to devise a partial activity series. Matter undergoes three kinds of change: physical, chemical, and nuclear. While the composition of a chemical substance is not altered by physical changes (such as freezing and evaporation), chemical changes, or reactions, result in the formation of new substances when bonds are formed and/or broken. Some relatively simple but common types of chemical reactions are illustrated in this experiment. Examples and descriptions of each reaction type appear in the following section. Chemical reactions are often accompanied by observable changes as they occur. These include: • Color change. • Formation of a precipitate—noted as the formation of a cloudy solution, formation of a gel, or • an obvious solid. • Evolution of a gas—noted as bubbling in the solution. • Appearance or disappearance of distinct separation between two or more liquids. • Evolution of heat—noted as a temperature increase. • Absorption of heat—noted as a temperature decrease. • Plating out of one metal on another. • Decomposition, pitting, or the disappearance of a solid...

Q. (a) What happens when propanoic acid is warmed with methanol in the presence of a few drops of concentrated sulphuric acid? Write equation of the reaction involved. (b) What change will you observe if you test soap solution with a litmus paper (red and blue)? Give reason for your observation. (c) What is meant by denatured alcohol? What is the need to denature alcohol?

Hint: Soaps are the potassium or sodium salts of fatty acids. Thus, we can say that they are salts of weak acid and strong base. Litmus paper shows red colour in pH range 0 to 7 and shows blue colour in pH range 7 to 14. Complete step by step solution: We will see the composition of soap and how litmus paper changes its colour upon the nature of the solution. - We know that soaps are sodium or potassium salts of fatty acids. The fatty acids are not as strong acids as mineral acids. Thus, we can call them the salt of weak acid and strong base. - We know that the salt of weak acid and strong base gives an alkaline solution when dissolved in water. Soaps give $NaOH$ and $KOH$ upon its dissolution in water. Alkaline solution has the pH range from 7 to 14. - Litmus paper has some dyes on the paper which are sensitive to the pH of the solution. It has its characteristic colour in different solutions. Litmus paper is available in two colours; red and blue. - When we dip a red litmus paper in the solution of soap, it will change its colour from red to blue. It shows that the solution is alkaline in nature. - When we dip a blue litmus paper in the solution of soap, then it remains blue in colour. Note: Note that we must require aqueous medium in order to check the pH of the solution by litmus paper. If we put dry litmus paper on solid soap without any presence of water on it, the red litmus paper will remain red.

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