Can I use baking powder in place of baking soda for dipping pretzels?
No, you cannot use baking powder to dip pretzels. To get their characteristic color and crust, pretzels are traditionally boiled in lye. Another alkaline solution, i.e. those containing a base, can be used as well. Let's look at how baking soda and powder are used as leavers:


Baking soda is a base (namely sodium bicarbonate) that releases carbon dioxide gas when mixed with an acid. That's why, in a recipe like buttermilk pancakes, acidic buttermilk can mix with baking soda to produce bubbles of gas that leaven the pancake.
Baking powder is a mixture of baking soda with a dry acidic substance. When mixed with water, it makes carbon dioxide gas all by itself.


Baking powder mixed with water will not be alkaline, since it contains both an acid and a base. Thus it won't work for boiling pretzels. Unfortunately, there aren't very many bases in your kitchen cabinets. While it is easy to substitute acids, the only bases you are likely to bake with are lye and baking soda.

If you skip the dipping step entirely, you will get plain rolls instead of pretzels. Boiling in plain water, or water with honey or barley malt syrup, will give you a more bagel-like crust. But to get a true pretzel, you really must boil in an alkaline solution.