While pound cakes traditionally rely on the creaming of butter and sugar for their structure and rise, the addition of a small amount of baking soda can provide some extra lift and lightness to the cake. Pound cakes typically contain a large amount of fat and sugar, which can make the batter heavy and dense. Baking soda, when combined with an acid or acidic ingredient like sour cream, creates carbon dioxide gas bubbles. These bubbles expand during baking and help the cake rise.