A student dips pH papers in solutions A and B and observes that the pH paper turns blue and orange respectively in them. What does he infer?
OR
A student took the following samples to find out their pH using pH paper: dilute hydrochloric acid, lemon juice, washing soda and soap solution. The teacher remarked that one of the samples taken was not proper. To which sample was the teacher referring to?
pH is a measure of acidity or basicity of an aqueous solution.
It is a mathematical notation that describes the power of an acid or a base. The concentration of the acid is represented as [H+] or [H3O+]
pH = – log [H+] (or)
pH = – log [H3O+]
The pH scale is the range of pH values from 0 to 14. The paper that indicates the complete range of pH value from 0 to 14 is called the universal indicator. pH paper is a strip of filter paper that is soaked in universal indicator and then dried.
When the pH value is between 0 and 7, it indicates the acidic range of the solution. When the value is between 7 and 14, it represents the basic or alkaline range of the solution. When pH = 7, it is called a neutral solution. The decrease of pH value indicates the increase of acidity and the increase of pH value shows the increase in alkalinity. Water is neutral and its pH is equal to 7.
Hence according to the question, he infers that A is sodium carbonate solution and B is acetic acid. The pH paper turns blue when dipped in solution A, it means A is a strong base having pH 9 and the pH paper turns orange when dipped in solution B, it means B is a strong acid having pH 4.
OR
pH is a measure of acidity or basicity of an aqueous solution.
pH paper is a strip of filter paper that is soaked in universal indicator and then dried.
From the samples what student has collected to test the pH value, washing soda is wrong selection.
Hence, the teacher was referring to washing soda because it is in powder form not in liquid form. To find pH using pH paper, the sample should be in liquid form.
Rest others - dilute hydrochloric acid, lemon juice, and soap solution are all in a liquid state and hence are good to be used for pH indication.
When the pH value is between 0 and 7, it indicates the acidic range of the solution. When the value is between 7 and 14, it represents the basic or alkaline range of the solution. When pH = 7, it is called a neutral solution. The decrease of pH value indicates the increase of acidity and the increase of pH value shows the increase in alkalinity.