Here's why:
* Acetic acid is a weak acid. It doesn't completely ionize in solution, meaning it doesn't release all of its hydrogen ions (H+).
* Litmus paper is a pH indicator. Red litmus paper is red in acidic solutions and turns blue in basic solutions.
* Since acetic acid is acidic, the red litmus paper will not change color.
Important Note: If the concentration of acetic acid is very high, it might be strong enough to slightly change the color of the litmus paper towards a more reddish-purple shade. However, it won't turn fully blue.
