You should be fine. I fly United almost exclusively (except for the upcoming trip on Song) and connect through Dulles (IAD) frequently.
50 Minutes to make a connection should not be a problem especially based on the time that you flying. Unless there is a weather delay in the morning, delays in air travel tend to happen later in the day and not first thing in the morning. Again weather plays a role in this and also the abundance of keeping the air traffic moving which gets backed up as the day progresses.
You will be flying a United Express flight from Syracuse to Dulles. Right now United is flying Jetstream 41's on that route. It's a turboprop and in my opinion, a really cool plane. The windows are extra large.
If you go to
www.united.com and go to the flight status tool, you can check each day to see how your flight is doing. For example, I plugged in your info today and the flight from Syracuse took off 10 minutes late and arrived at Gate A6. Your connection to MCO took off 5 minutes early and departed from Gate D4.
Dulles makes connecting to different terminals rather easy, because you load a "bus" that actually attaches itself to the terminal building and travels along the tarmac over to the other terminal.
In all my years of flying, I have only missed one connection at Dulles and my connecting flight at that time was still in the same terminal.
I suspect you will have no problem making your connection. Jetstream 41's are small enough and they unload very quickly.
Enjoy!