Is cocoa powder chocolate?
Cocoa is a powder made from roasted and ground cacao beans. The beans are harvested, fermented, dried, roasted, cracked into nibs and then pressed to remove much of their butter.  The remaining cocoa liquor is dried and ground into unsweetened cocoa powder. This results in what is known as natural cocoa powder.  

Dutch process cocoa powder begins with beans that have been washed in potassium carbonate, which neutralizes their acidity.  This makes the powder darker, it alters the flavor, and increases solubility. 

Chocolate is made using the same process, but the cocoa butter remains. This results in unsweetened chocolate.  Of course, sugar is added to the sweetened varieties. The percentage of cocoa bean indicates the bitterness level of the chocolate.  Chocolate can also have dairy added (milk chocolate).

So, cocoa is a raw product. It is use to make cocoa powder and chocolate.  There are brownie recipes that include chocolate, recipes that only use cocoa powder, and those that use both.  You'll have to determine into which category your brownies fall.