Originally Posted by Moni

Depending on the context, "vuelque" and "vacíe" may be used as synonyms, but they are not. "Volcar" means to pour, while "vaciar" means to empty. So, if you talk about half of the mixture, "volcar" is more correct, since you don't empty the container. Anyway, it's a subtlety, anyone would perfectly understand if you say "vacíe la mitad de la mezcla".