A CRJ-700 First Officer reports the Captain's desire to fly at 250 kts when previously assigned 300 kts because of three wake turbulence encounters on approach to ORD. This was the First Officer's first career wake turbulence encounter.

Narrative

We were on the radio with Chicago Approach. We were assigned 330 knots about 5 minutes prior to the occurrence. We were maintaining the 300 knots. As the pilot not flying; I was completing the 'in range checklist' when we encountered wake turbulence. It was the first time I have experienced wake turbulence. The Captain controlled and stabilized the aircraft. We were asked 'say speed' by approach; I looked up from the checklist and replied '250 knots.' They reassigned us 300 knots. We then hit turbulence again. The second time was more violent than the first; and the Captain clicked off autopilot and hand flew the aircraft slightly above the glide slope to alleviate encountering any further turbulence. The Captain asked me to advise the Approach Controller of the wake turbulence we were encountering (then we hit our third pocket of wake turbulence); however the radio was too saturated to do so; until we were established on the approach. We then told the Controller that we had encountered turbulence three times; eliciting no reply. Then they came back on the radio and assigned us a number to call. The Captain told me during the event that he was acting in what he thought was the safest manner possible. I believe this to be the case as well. I had no prior experience with wake turbulence and given the events; I believe his actions clearly took safety as the priority.