Question

how we can test the presence of an acid in a substance by performing the litmus test ???

Answer 1

Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic or alkaline conditions, with the color change occurring over the pH range 4.5–8.3 at 25 °C (77 °F). Neutral litmus paper is purple. Litmus can also be prepared as an aqueous solution that functions similarly...

Answer 2

Basically litmus papers are used as indicators to test whether the given substance is acidic, basic or neutral in nature.

So the function of litmus is used as follows.....

Basically we know whether the substance is acid or basic due to our advanced technology

So for the bases we use red litmus paper and if the red litmus turns blue we are 100% sure about its nature tha it is basic and if somebody asks u how will we come to know which litmus paper to take...then test using the two litmus papers simultaneously as if the substance is basic and we are using the blue litmus paper then it will show no change but that leads to question if it is neutral or not but then we can do neutralisation reaction for the same

And then it comes to acids

For acids we will use blue litmus paper because it will turn red and the changing of blue to red colour will assure you that it is acid in nature and we can use red litmus paper also if we are not sure then it will show no change but again it leads to the question whether it would be neutral or not then again we can do neutralisation reaction.

Hope it helps