which recipe did you use?

did you use the chocolate cake recipe? that's the only step-by-step cake recipe I posted. if that's the one you made, it shouldn't be hard, you don't need a big mixer for the egg whites, however, different oven perfomes differently, so you need to use a chopstick to test whether or not the cake is ready(stick it in the middle of the cake and pull out, if there's any stuff sticky to the chopstick then it is not ready yet. leave it in the oven for a little bit longer until the chopstick test come out clean). other than that i don't think the baking soda would be the problem(unless it has already expired), please let me know which recipe you used and if there's any step you skipped. :)