Have made your choc chip cookie recipe with great success several times now. My understanding is that baking powder just needs liquid to become active whereas baking soda requires an acid. Can someone tell me please where the acid is in this recipe.

the acid comes from brown sugar. also, baking soda is activated by heat as well. try placing a mound of baking soda each of two plates, then pour cold water on one and hot water on the other. watch the difference in the activity of the two - with temperature being the only difference.