Mine is stuck on 75/80 and no matter how many more i collect the progress remains the same. I really like this modpack but now im stuck and cant do anything

This happens sometimes. Try just opening a chest and this should re-sync your quest so it completes properly.

That doesn’t seem to work, ive been opening chests all the time and it hasnt helped

That's odd.. what version of the pack are you playing? Also, please double check that it's actually potassium chloride that you have and not some other compound.

I know this is a year old, but I had this problem yesterday. If you have the items in a drawer, it doesn't seem to count them. Pull them all out of the drawer and into your inventory.