A litmus paper was dropped into 2ml dilute HCl. Then 2ml concentrated NaOH was added to it and stirred.

Question

Write down the changes that will be seen in each 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

Blue litmus Paper:

• HCl is hydrochloric acid, so the blue litmus turns red.
• When equal amount of NaOH is added the colour again changes to blue and remains the same.

Red litmus paper:

• Red litmus paper shows no colour change in hydrochloric acid. 
• When some amount of NaOH is added the colour changes to blue initially but when the amount of NaOH is sufficient the blue colour dissappears. 
• Equal amounts of HCl and NaOH results in the formation of NaCl, a salt, and the solvent water. This reaction is called the neutralization reaction.