What Am I Riddles

Question: What's always coming, but never arrives?

Question: When you do not know what I am, then I am something. But when you know what I am, then I am nothing. What am I?

Question: What is harder to catch the faster you run?

Question: You answer me, but I ask you nothing. What am I?

Question: Round like a dishpan and smaller than a bathtub.But the ocean can't fill it.What is it?