vinegar(lemon juice and other acidic liquids), buttermilk, cocoa powder and brown sugar will remove a bitter taste that baking soda will leave in baked goods too. If you ever see a recipe that has baking soda and does not have either a large amount of baking powder or one or more of the above ingredients, it is not a good recipe...unless you want that flavorAha! Ok, I'm awake enough now to find info on it
what-is-the-purpose-for-vinegar-in-red-velvet-cake
Interesting!