Should I ask for more compensation?

Hi all,

My boss informed me today that our co-worker is leaving the company after 5-months. She was hired to replace someone else who left (took 6 months to hire) and within that time I picked up the work with no pay raise. This time around I want to ask for a raise. Is it reasonable? How should I approach it? I have a student on my team this time that can help.. but most of the responsibility will fall on me. I recently received a 3.5% raise at the end of Jan (year-end bump) So is it reasonable to ask for more?

Thanks.