Approximately 8 months ago I was promised a raise of $0.80 an hour but never got it, am I entitled to any of that back pay?

It seems that you have written documentation from your former employer that you were to get an .80 per hour raise. Was there a set date mentioned? If there was, perhaps sending a letter to your former employer seeking the additional money owed and a calculation as to the total amount owed is on order to see if you can voluntarily get payment for what was promised and seemingly agreed to by you.

Keep a copy of the letter for future need if be.

If your former employer does not come up with an amount owed you for the .80 per hour raise, perhaps contacting your State's labor department to discuss the situtation is the way to go.

From the facts given me, it seems that you would be entitled from your former employer the raise of .80 per hour not given you but promised in writing.