Why the leavening matters more than the cocoa amount
Natural cocoa powder is genuinely acidic — that acidity is exactly what a recipe's baking soda needs to react with and produce lift. Dutch-process cocoa is treated with an alkalizing agent that neutralizes most of that acidity, giving it a smoother flavor and darker color, but also removing the acid a recipe might be counting on. Baking powder carries its own acid built in, which is why Dutch-process cocoa recipes typically use baking powder instead of soda. Black cocoa is Dutch-process cocoa taken further — even more alkalized, even darker, and chemically similar enough to regular Dutch-process that it needs the same treatment.
What actually changes when you swap
The cocoa amount itself never changes — it's always a 1:1 swap by volume regardless of type. Color and flavor shift with the type (natural is lighter and more sharply chocolatey, Dutch-process is darker and smoother, black is nearly black with a very mild flavor, mostly used for color and Oreo-style desserts). The part that actually breaks a recipe if ignored is the leavening — swap across the acidic/alkalized line without adjusting it, and the cake either won't rise properly or will taste faintly metallic from unreacted baking soda.
FAQ
How can I tell which type a recipe uses if it doesn't say? Check the leavening: a recipe using only baking soda for a chocolate cake is almost always built for natural cocoa; one using only baking powder (or both) is more likely written for Dutch-process.
Does black cocoa taste different enough to matter? Yes — it's noticeably milder and more bitter than either natural or regular Dutch-process, which is why it's usually blended with another cocoa rather than used entirely on its own, except when the goal is that very dark, Oreo-style color and mild flavor.