Assuming that the [Potato extract] is .001 M and I am going to make a 10 ml solution and each drop is 1/20th of a mL, how do I calculate the [Potato extract] in each reaction solution, using 20 drops, 15, 10, and 5 drops for each one?

This must be an exciting experiment but I don't know what you're doing. Please try to clarify the post.