A group of students is given two beakers labelled A and B by the teacher. One beaker was filled with dilute nitric acid, and the other with dilute sodium hydroxide solution. The teacher then instructed students to use the phenolphthalein indicator to determine which beaker contained nitric acid and which beaker contained sodium hydroxide solution. Students used phenolphthalein to test both beakers and obtained the results. Beaker A contains sodium hydroxide solution, while Beaker B contains the nitric acid solution.
Based on the above understanding, how does the phenolphthalein indicator work? Is phenolphthalein a natural or human-made indicator? Explain your answer.
Important Questions on Acids, Bases and Salts
Rajiv was eating "curd curry with rice" popularly known as Kadhi chawal. Mistakenly the curry was spilt on the white shirt of Rajiv, and it got a yellow stain of curry. The next day, when Rajiv's mother was doing laundry, he observed that as soon as her mother rubbed the curry stain with the soap cake, the yellow stain turned reddish-brown.
On rinsing the shirt with plenty of water, the reddish-brown stain turned yellow again. Name the natural indicator which is possibly present in curry stain on Rajiv's shirt. Also help Rajiv to understand the reason behind these colour changes.
