Is it normal for the exposed layer of skin to peel or slough in a second degree burn?

Yes. A second degree burn involves a partial thickness injury to the skin. The epidermis usually separates from the dermis and often forms fluid filled blisters. Usually the damaged superficial layer of skin peels or sloughs off as the skin underneath heals. This peeling can also happen in some 1st degree burns (e.G sunburn).
Yes. A second degree burn by definition is a partial thickness ( of the skin) burn. This means the burn does not go through the full skin layers. There are usually blisters in a second degree burn and the outside layer of skin typically sloughs.