Your examples all call for adjectives. The one you said you were sure about is "educational." If the other option is "education" it wouldn't work because it's a noun. "It was a very education experience"?
The ones you were unsure of each seem to be a pair of (1) an adjective, and (2) a [psuedo] adjective, or an incorrect or nonexistent form of the word, often incorrectly used by many people. (Sorry, both ironic and ironical are acceptable as adjectives. Ironically is the adverb.)
As Philip suggests, your dictionary should make it clear which one exists as an adjective and which one is either some other part of speech, or doesn't exist at all.
For example, idiotical and narcissistical don't exist. The adjectives end in "c" and the adverbs go to "cally." Egotist, on the other hand, allows both egotistic and egotistical as adjectives, with egotistically as the adverb. Irony works the same way as egotist. You just have to look them up.
Perhaps if you need a rule of thumb, when you're trying to decide between a short one ending in "c" and a longer one ending in "l", go for the short one.
Best regards, - A.