Can baking powder be used instead of baking soda for face whitening?

NO!!! Please see a certified dermatologist for best results.
Both work the same. Baking powder, baking soda, and white flour are white in color, and will make one's face look whiter during the time that these white substances are on the face. Of course, one would look quite odd at that time, being covered with whitish substances. As soon as the stuff is washed off, the skin is as before, no lighter, no darker. So, baking powder and baking soda work the same, as neither work.
Colorism. Physicians don't recommend either for face whitening. The more important question is why do you want to lighten your skin? Has your life been affected by "Colorism", the prejudice against darker color skin? If so, you may want to go to this website where a physician from India(where Colorism is rampant) discusses the subject>>>