Original thread: https://www.physicsforums.com/threads/remove-an-aluminum-tube.952459/ NaHCO3, i.e. sodium hydrogen carbonate, compared to neutrality, is a weakly alkalinic salt, which, although it can, in the presence of a stronger base, such as sodium hydroxide, act as an acid, by surrendering its hydrogen, is not correctly designated as by itself an acid. Adding baking soda to lye, the reaction is NaOH + NaHCO3 → Na2CO3 + H2O, i.e. disodium carbonate (commonly called sodium carbonate, or washing soda) plus water. Although that's less alkalinic than NaOH, in solution the disodium carbonate ionizes as 2 sodium ions plus H2CO3 (carbonic acid -- CO2 plus H2O), and that's still more strongly basic than baking soda -- if you add in baking soda alone, you can't fully titrate lye to neutrality.