A B737 FLT CREW IS FORGOTTEN ABOUT BY IAD APCH.

Narrative

I; THE FO WAS FLYING ON THE EM13 ARR TO BWI. DURING THE FINAL SEGMENT OF THE ARR WE WERE SWITCHED FROM CTR TO DULLES APCH. DULLES APCH GAVE US A VERY STANDARD 'DSND TO 5000 FT TURN HEADING 100 DEGS.' CRUISING AT 5000 FT WE WERE IN VFR WITH GOOD VISIBILITY; THE ARPT WAS IN SIGHT. WHEN WE REACHED THE POINT WHERE WE WOULD NORMALLY MAKE A TURN S TOWARD THE ARPT; I ASKED THE CAPT 'WHERE IS HE (ATC) TAKING US?' THE CAPT REPLIED HE WAS THINKING THE SAME THING. THE ENTIRE TIME WE WERE APCHING THERE WAS CONSTANT RADIO CHATTER BTWN DULLES AND OTHER ACFT. WHEN ATC WAS QUESTIONED ABOUT A TURN; THE CTLR SEEM CONFUSED AND COULD NOT GIVE US ANY INSTRUCTION. NOT WANTING TO STRAY TOO FAR FROM A NORMAL APCH PATH THE CAPT SWITCHED TO A KNOWN BWI APCH FREQ AND MADE CONTACT. WE WERE VECTORED TO THE VISUAL RWY 33L WITH A NORMAL LNDG. BWI GND CTL REQUESTED THAT WE CONTACT THE TRACON AND GAVE A PHONE NUMBER. THE CAPT MADE THE CALL. I AM UNCERTAIN AS TO HOW OR WHY WE DID NOT RECEIVE A SWITCH TO BWI APCH SOONER OR WHY THE CTLR WE HAD; LOST US OR IF A MISSED FREQ WAS MADE ON BOARD OUR ACFT.