Actually there were both Union and Confederate Cavalry units that were designated as the 2nd Arkansas. On the Union side thre were the 1st, 2nd, 3rd, and 4th Arkansas Cavalry (Union) and the same numbers Confederate. Infact, the Confederates have about six units that were at some time referred to as the 1st Arkansas Cavalry.

You can determine the side that the unit fought for based on the numerical designation.