In the early 1900's a pitching wedge was referred to as a "lofter" and had between 40 and 50 degrees of loft. Shortly thereafter, sets of golf clubs were given numbers, and the modern-day pitching wedge was called a 10-iron. Now a set of irons will include a pitching wedge with a loft of between 45 and 48 degrees.
For most of the 20th century the pitching wedge had approximately 50-54 degrees of loft. Since the 2000s, the lofts of all irons have been decreased because of perimeter weighting and changing the center of gravity on irons to allow the ball to fly farther. Now the average loft of a new pitching wedge is 46-50 degrees. The sand wedge, on the other hand, is and always has been between 54 and 56 degrees, creating a large gap between it and the modern pitching wedge.
Most pitching wedges have a similar look as the rest of the irons in a set. Other wedges are specialty wedges that appear more like a sand, gap or lob wedge, such as Titleist's Vokey 48-degree wedge. Wedges will be progressively shorter than a 9-iron and slightly more upright.
A good idea is to have the lofts of all your irons and wedges checked at a reputable golf equipment shop. Depending upon your 9-iron's loft and your wedge lofts, you will be able to determine the best loft for your pitching wedge.