Alright, I followed the instructions on rune tip it for this quest. It tells you where the key should spawn. I went to that chest and kept searching it it. It kept saying this chest is empty. Then i checked every other chest and found nothing but anti poison and spiders.

 

What am i doing wrong and what should i do!!??

I'd say just close chest and check everyone again after you left the dungeon to refresh.

It spawns in a random chest: just keep on searching, and eventually you'll find it, along with quite a number of spiders on the way I'm sure.