When exposed to solutions under a pH of 7, it turns red because the solution is acidic. When exposed to a solution that has a higher pH of 7 or above, the solution is alkaline, and it turns litmus paper blue. If the solution is neutral,
( pH of 7 ) then the litmus paper will turn purple.
What you are looking for is ACID so the litmus paper will turn RED.
Nothing happens to these particles when it comes to size however if it were to be speed, the sample would increase. Fact: The size of a particle will never change!
