Question

Write down the changes that will be seen in this instance and explain the reason behind it.
"A litmus paper was dropped into 2ml dilute HCl. Then 2ml concentrated NaOH was added to it and stirred."

Answer 1

When a litmus paper is dropped in 2 ml dilute HCl solution. The litmus paper shows red colour.
When 2 ml concentrated NaOH is added to the solution, NaOH neutralises HCl, but due the higher concentration of NaOH solution, NaOH becomes in excess. The solution becomes basic.
The red litmus paper then changes to blue.