I am a salaried employee. I work a 40 hour week in a five day period. Can i legally be made to work a 48 hour week in a six day period with only one day off...not getting paid but for just 40 hours? Can I be compensated with on more day off during the week to keep my work week at 5 days?

I'm going to assume that by salaried you mean exempt.

Your salary covers all the hours you work, no matter how many or how few; not just 40. You can be required to work as many hours as your employer feels they need you to work. No law in any state requires that you get two days off per week, and neither DC nor Texas requires even one day off per week. There are NO circumstances, no matter how many hours or days are worked, when an exempt employee is entitled by law to additional compensation over and above their regular salary.