is there a difference between cake flour and all purpose flour?
Yep...big difference. By weight, cake flour weighs 4 oz. per cup and all-purpose flour weighs 4.5 oz. per cup. Cake flour makes for a finer crumb and a more tender cake. All-purpose flour makes sturdier cakes if that's what you're looking for. Hope that helps!
Besides the difference in weight, cake flour has less protein content than AP flour and will result in a more tender, softer crumb.
To substitute cake flour for all-purpose flour use 1 cup plus 2 tablespoons cake flour for every cup of all-purpose flour.