Originally Posted by muckety
Good question (and answer) - I understand that Baking powder acts as a raising agent, does Bicarb of Soda do the same or what is the purpose of it in recipies?
Basically, plain bicarbonate of soda reacts with other weakly acid ingredients in the recipe, such as buttermilk in scone and soda bread recipes, to do the same thing, i.e. act as a raising agent.
You also see recipes for things like soda bread or scones that specify using baking powder instead of bicarb, or that specify a mix of bicarb and cream of tartar, which is one of the ingredients of commercial baking powder. I don't know the reasons for using the one over the other, I'm afraid, maybe it's just a belts and braces approach in case the buttermilk or whatever isn't acidic enough to cause enough rising.