[werrl]

Hello,
I am having trouble determining whether something is an acid or a base. I know the strong acids and that strong bases are group 1 and Ca²⁺ , Ba²⁺ , and Sr²⁺ . However, I keep coming across problems in my textbook where I am still labeling an acid a base or vice versa. How can I determine which is which?!

I know the amphiprotic ions can act as either a base or acid.
Examples of my confusion: In my book, it asks to label as either a strong base, a weak base, or something with negligible basicity:
1) It says O^2- would be a strong base. I would think it would be negligible. Why would this be a strong base?
2) It says Cl^- would be a negligible base. If this is a negligible base, why is O^2- a strong base?

Thanks!
Edit: I'm also having trouble understanding how to predict whether the equilibrium lies to the right or the left. I remember reading that it favors the reaction that moves a proton to the stronger base, but I'm a little confused on this subject. Could someone please clarify? Thanks

[Borek]

1) It says O^2- would be a strong base. I would think it would be negligible. Why would this be a strong base?

What is the definition of a base?